Java

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📘 Java Topic 1: What is Java?

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🔹 Java Definition

Java is a high-level, object-oriented, platform-independent programming language used to develop software, web, desktop, mobile, and automation tools.

📖 Nepali Insight:
Java एकदमै popular programming language हो जुन एकपटक लेखेर धेरै platform मा चलाउन सकिन्छ (write once, run anywhere concept)।

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🔹 Why Java is Important for QA Engineers

Reason	QA Use
Selenium Support	Most Selenium frameworks use Java
Test Frameworks	TestNG, JUnit built in Java
Backend Testing	Used in REST API, database layers
OOP Concepts	Important for Page Object Model
Industry Demand	Java QA jobs are in high demand

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🔹 Java Program Structure Example

java

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public class HelloWorld {

    public static void main(String[] args) {

        System.out.println(“Hello, Lok!”);

    }

}

📖 Explanation:

• public class HelloWorld: Class name
• main(): Entry point
• System.out.println(): Print to console

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🔹 Key Java Features

Feature	Description
Object-Oriented	Everything is based on objects
Platform Independent	Compile once, run anywhere (via JVM)
Strongly Typed	Every variable must have a type
Multithreaded	Supports parallel execution
Secure & Robust	Built-in memory management

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🔹 Basic Java Terms

Term	Meaning
Class	Blueprint or template
Object	Instance of a class
Method	Action performed (like function)
Variable	Stores value
Data Type	Type of data (int, String, boolean)

📘 Java Topic 2: Data Types, Variables, and Operators

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🔹 What is a Variable?

A variable is a container in memory that stores data. You can change the value stored in it during program execution.

📖 Nepali View:
Variable भन्नाले data राख्न प्रयोग गरिने memory को नाम हो। यो changeable हुन्छ।

🧠 Example:

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int age = 30;

String name = “Lok”;

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🔹 Types of Variables in Java

Type	Description
Local Variable	Defined inside a method
Instance Variable	Defined inside a class but outside any method
Static Variable	Shared by all objects (declared with static)

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🔹 What is a Data Type?

A data type defines the type of value a variable can hold (integer, decimal, character, etc.).

📖 Nepali Insight:
Data Type ले variable भित्र कस्तो प्रकारको value राख्न सकिन्छ भनेर define गर्छ।

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✅ Java Data Types

🔸 1. Primitive Data Types (8 total)

Type	Size	Example	Use
int	4 bytes	int age = 25;	Whole number
float	4 bytes	float pi = 3.14f;	Decimal with f
double	8 bytes	double salary = 9999.99;	Large decimal
char	2 bytes	char grade = ‘A’;	Single character
boolean	1 bit	boolean status = true;	True/False
byte	1 byte	byte x = 100;	Small number
short	2 bytes	short y = 30000;	Medium number
long	8 bytes	long z = 123456789L;	Big integer with L

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🔸 2. Non-Primitive Data Types

Type	Description	Example
String	Text	String name = “Lok”;
Array	Multiple values	int[] nums = {1, 2, 3};
Class	Custom type	Person lok = new Person();

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🔹 Java Operators

Operators are symbols that perform operations on variables and values.

📖 Nepali Insight:
Operator भन्नाले कुनै काम गराउने चिन्ह हो, जस्तै जोड्ने, घटाउने, compare गर्ने आदि।

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✅ Types of Operators

Category	Operators	Example
Arithmetic	+, -, *, /, %	a + b, a % b
Relational	==, !=, <, >, <=, >=	a > b
Logical	&&, `
Assignment	=, +=, -=, *=	a += 5
Unary	++, —	i++, –i
Ternary	? :	a > b ? a : b

🧠 Example:

java

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int a = 5;

int b = 10;

int max = (a > b) ? a : b;

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✅ Summary

Concept	Example	QA Use
Variable	int age = 30;	Store dynamic data
Data Type	boolean isValid = true;	Define type of value
Operator	if(a > b)	Perform logic in code

📘 Java Topic 3: Conditional Statements (if, else, switch)

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🔹 What are Conditional Statements?

Conditional statements allow your program to make decisions — to execute certain code only if a specific condition is true.

📖 Nepali Insight:
Conditional statement ले भन्न सक्छ — “यदि यस्तो भयो भने यस्तो गर, नभए अर्कै गर।”

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✅ 1. if Statement

Executes a block of code only if the condition is true.

java

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int age = 18;

if (age >= 18) {

    System.out.println(“Eligible to vote”);

}

📖 Nepali: यदि उमेर १८ वा बढी छ भने मतदान गर्न मिल्छ।

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✅ 2. if…else Statement

Adds an alternate block to execute if the condition is false.

java

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if (age >= 18) {

    System.out.println(“Eligible to vote”);

} else {

    System.out.println(“Not eligible”);

}

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✅ 3. if…else if…else

Used to check multiple conditions.

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int score = 75;

if (score >= 90) {

    System.out.println(“Grade A”);

} else if (score >= 75) {

    System.out.println(“Grade B”);

} else {

    System.out.println(“Grade C”);

}

📖 Nepali: कुन-कुन level मा के काम गर्ने भनेर step-wise check गर्न।

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✅ 4. switch Statement

Used to select one of many code blocks to execute — better than using many else if for specific cases.

java

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int day = 3;

switch (day) {

    case 1: System.out.println(“Sunday”); break;

    case 2: System.out.println(“Monday”); break;

    case 3: System.out.println(“Tuesday”); break;

    default: System.out.println(“Invalid”);

}

📖 Nepali: दिन अनुसार के देखाउने भन्ने कुरा चुनिन्छ।

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🔹 Notes on switch:

• break prevents fall-through (stops execution after match)
• default is optional but handles unmatched cases

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✅ When to Use What?

Use Case	Statement
One simple condition	if
Either this or that	if…else
Multiple conditions	if…else if…else
Multiple known fixed values	switch

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🧪 QA Use Example

You may use these in:

• Test data generation logic
• Conditional validation scripts
• Flow control in automation framework (TestNG, Selenium)

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📘 Java Topic 4: Loops (for, while, do-while)

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🔹 What is a Loop?

A loop is used to execute a block of code repeatedly until a specific condition is met.

📖 Nepali Insight:
Loop ले एकै काम बारम्बार गराउँछ — जति पटक चाहिन्छ, उति पटक।

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✅ 1. for Loop

Used when the number of iterations is known or fixed.

java

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for (int i = 1; i <= 5; i++) {

    System.out.println(“Hello ” + i);

}

📖 Example Output:

nginx

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Hello 1

Hello 2

Hello 3

Hello 4

Hello 5

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✅ 2. while Loop

Used when the number of iterations is unknown, but depends on a condition.

java

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int i = 1;

while (i <= 5) {

    System.out.println(“Hello ” + i);

    i++;

}

📖 Nepali: while ले पहिले condition check गर्छ अनि मात्र loop चलाउँछ।

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✅ 3. do…while Loop

• Executes the loop at least once, even if the condition is false at first.
• Condition is checked after one full execution.

java

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int i = 1;

do {

    System.out.println(“Hello ” + i);

    i++;

} while (i <= 5);

🧠 Use this when you want the action to happen at least one time.

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🔹 Loop Flow Summary

Loop Type	Condition Checked	Runs at least once?
for	Before start	Only if true
while	Before start	Only if true
do…while	After first execution	✅ Always once

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🔹 Common QA Use Cases

• Data-driven testing: Loop through data
• Retry logic: Keep trying until status = “Success”
• Batch verification: Loop over rows, items, or fields

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🔹 Example – Print Even Numbers from 1 to 10

java

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for (int i = 1; i <= 10; i++) {

    if (i % 2 == 0) {

        System.out.println(i);

    }

}

📖 Output:

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2

4

6

8

10

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✅ Bonus: Enhanced for-each Loop (For Arrays/Collections)

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String[] cities = {“Dallas”, “Austin”, “Houston”};

for (String city : cities) {

    System.out.println(city);

}

📘 Java Topic 5: Arrays and Strings

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🔹 What is an Array?

An array is a data structure that stores multiple values of the same type in a single variable, using an index to access each element.

📖 Nepali Insight:
Array भन्नाले एकै नाममा धेरै समान प्रकारका data राख्न मिल्ने list हो — जसमा प्रत्येक item को number (index) हुन्छ।

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✅ Array Declaration & Initialization

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int[] numbers = {10, 20, 30, 40, 50};

🧠 Indexing starts from 0:

• numbers[0] = 10
• numbers[1] = 20

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🔹 Accessing Array Elements

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System.out.println(numbers[2]); // Output: 30

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🔹 Looping Through Array

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for (int i = 0; i < numbers.length; i++) {

    System.out.println(numbers[i]);

}

✅ Output:

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10

20

30

40

50

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🔹 for-each Loop

java

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for (int num : numbers) {

    System.out.println(num);

}

📖 Nepali: Array का सबै elements एक-एक गरेर access गर्न सजिलो तरीका।

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🔹 String in Java

A String is a sequence of characters. It is an object in Java, not a primitive data type.

java

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String name = “Lok QA”;

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✅ String Methods

Method	Purpose	Example
length()	Length of string	name.length() → 6
charAt(index)	Character at index	name.charAt(0) → ‘L’
toUpperCase()	Convert to caps	name.toUpperCase()
toLowerCase()	Convert to small	name.toLowerCase()
equals()	Compare (case sensitive)	“Lok”.equals(“lok”) → false
equalsIgnoreCase()	Compare (ignore case)	→ true
contains()	Check substring	name.contains(“QA”) → true
substring(x, y)	Extract part	name.substring(0, 3) → “Lok”
split()	Break string into parts	“A-B-C”.split(“-“)

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🔹 String Concatenation

java

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String first = “Lok”;

String last = “Subedi”;

String full = first + ” ” + last;

System.out.println(full);  // Lok Subedi

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🔹 Immutable Nature of Strings

Strings in Java are immutable — once created, they cannot be changed.

📖 Nepali: String लाई change गरेजस्तो लागे पनि Java मा actually नयाँ object बन्छ।

✅ Use StringBuilder or StringBuffer for mutable strings in performance-heavy applications.

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🧪 QA Use Examples:

• Parse test data (e.g., split values)
• Validate text from UI/API
• Loop over data sets stored in arrays

📘 Java Topic 6: Object-Oriented Programming (OOPs) Concepts

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🔹 What is OOP?

OOP (Object-Oriented Programming) is a programming paradigm where real-world entities like objects, classes, and relationships are used to design software.

📖 Nepali Insight:
OOP भन्नाले सबै कुरा object (वास्तविक वस्तु) को रूप मा सोची software design गर्ने तरिका हो।

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✅ 4 Pillars of OOP

Principle	Description	Example
Encapsulation	Bind data and code in a single unit (class)	Use of private variables + public methods
Inheritance	One class inherits from another	Child extends Parent
Polymorphism	One method behaves differently	Method Overloading / Overriding
Abstraction	Hide complex logic, show only essentials	Abstract classes/interfaces

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🔸 1. Encapsulation

• Wrapping data (variables) and code (methods) into a single unit (class)
• Achieved using private variables and public getters/setters

java

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public class Student {

    private String name;

    public void setName(String newName) {

        name = newName;

    }

    public String getName() {

        return name;

    }

}

🧠 Used in test frameworks to protect variables and control access.

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🔸 2. Inheritance

• One class inherits properties/methods of another class using extends keyword

java

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class Vehicle {

    void start() { System.out.println(“Starting…”); }

}

class Car extends Vehicle {

    void horn() { System.out.println(“Beep!”); }

}

🧠 POM frameworks use inheritance to avoid repeating common code.

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🔸 3. Polymorphism

• Same method, different forms
• Two types:
  • Compile-time (Method Overloading) – same method name, different parameters
  • Runtime (Method Overriding) – child class overrides parent method

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class MathOps {

    int add(int a, int b) { return a + b; }                  // Overload 1

    double add(double a, double b) { return a + b; }         // Overload 2

}

class Parent {

    void greet() { System.out.println(“Hello Parent”); }

}

class Child extends Parent {

    void greet() { System.out.println(“Hello Child”); }     // Override

}

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🔸 4. Abstraction

• Hiding implementation details and showing only functionality
• Achieved via:
  • Abstract class (can have abstract + normal methods)
  • Interface (100% abstract in older Java versions)

java

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abstract class Animal {

    abstract void sound();

}

class Dog extends Animal {

    void sound() { System.out.println(“Bark”); }

}

🧠 Interfaces like WebDriver, Runnable in Selenium are examples of abstraction.

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🔹 Class vs Object

Term	Meaning
Class	Blueprint/template
Object	Instance of a class (actual entity in memory)

java

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class Book {

    String title;

}

public class Main {

    public static void main(String[] args) {

        Book b = new Book(); // Object created

        b.title = “Java Notes”;

    }

}

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✅ Summary Table

Concept	Meaning	Keyword
Encapsulation	Protect data	private, get, set
Inheritance	Reuse code	extends
Polymorphism	Flexibility	@Override, method overloading
Abstraction	Hide logic	abstract, interface

📘 Java Topic 7: Class, Object, Constructor, this, and super Keywords

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🔹 What is a Class?

A class is a blueprint/template used to create objects. It defines properties (variables) and behaviors (methods) of an object.

📖 Nepali Insight:
Class भन्नाले एउटा design हो — जसको आधारमा object तयार हुन्छ।

java

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public class Car {

    String color;

    void start() {

        System.out.println(“Car started”);

    }

}

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🔹 What is an Object?

An object is an instance of a class — the real, memory-allocated version of the blueprint.

java

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public class TestCar {

    public static void main(String[] args) {

        Car myCar = new Car();  // Object creation

        myCar.color = “Red”;

        myCar.start();          // Method call

    }

}

🧠 Multiple objects can be created from the same class with different data.

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🔹 Constructor in Java

A constructor is a special method that is automatically called when an object is created.

📖 Nepali View:
Object बनाउँदा जे काम तुरुन्तै चलाउनु पर्छ, त्यो constructor भित्र राखिन्छ।

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✅ Types of Constructors

Type	Description
Default Constructor	No arguments
Parameterized Constructor	Takes arguments to initialize object

java

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class Person {

    String name;

    // Constructor

    Person(String personName) {

        name = personName;

    }

    void greet() {

        System.out.println(“Hello ” + name);

    }

}

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🔹 this Keyword

Refers to the current object’s instance. Often used when local and instance variables have the same name.

java

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class Student {

    String name;

    Student(String name) {

        this.name = name;  // ‘this’ refers to the current object

    }

}

📖 Nepali Insight:
this ले “म यो object भित्रको variable हो” भनेर जनाउँछ।

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🔹 super Keyword

Refers to the parent class. Used to:

• Call parent’s constructor
• Access parent’s variable/method

java

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class Animal {

    String sound = “Generic sound”;

}

class Dog extends Animal {

    void printSound() {

        System.out.println(super.sound);  // Accessing parent variable

    }

}

Also used as:

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super(); // Calls parent class constructor

📖 Nepali View:
super ले भन्न सक्छ — “म parent class को कुरा गर्दैछु।”

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✅ Summary Table

Concept	Description	Keyword
Class	Blueprint of object	class
Object	Instance of class	new
Constructor	Auto-runs when object created	ClassName()
this	Refers to current object	this.variable
super	Refers to parent class	super.variable or super()

📘 Java Topic 8: Inheritance in Depth (Types, Constructors, Method Overriding)

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🔹 What is Inheritance?

Inheritance is the process by which one class (child/subclass) inherits properties and behaviors from another class (parent/superclass).

📖 Nepali Insight:
Inheritance भन्नाले एउटा class ले अर्को class को गुण र काम (method) अपनाउनु हो।

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✅ Why Use Inheritance?

Benefit	Description
Code Reusability	Common code lives in parent class
Maintainability	Logic change in one place applies to all
Scalability	Helps in framework design (like POM in Selenium)

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✅ Syntax

java

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class Parent {

    void greet() {

        System.out.println(“Hello from Parent”);

    }

}

class Child extends Parent {

    void show() {

        System.out.println(“I am the Child”);

    }

}

java

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Child c = new Child();

c.greet(); // Inherited from Parent

c.show();  // Own method

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🔹 Types of Inheritance in Java

Type	Description	Support in Java
Single	One child, one parent	✅
Multilevel	Parent → Child → Grandchild	✅
Hierarchical	One parent, many children	✅
Multiple	Multiple parents (via classes)	❌ (only via interfaces)

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🔸 Single Inheritance

java

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class Animal {

    void eat() { System.out.println(“Eating”); }

}

class Dog extends Animal {

    void bark() { System.out.println(“Barking”); }

}

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🔸 Multilevel Inheritance

java

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class Animal {

    void eat() {}

}

class Dog extends Animal {

    void bark() {}

}

class Puppy extends Dog {

    void weep() {}

}

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🔸 Hierarchical Inheritance

java

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class Animal {

    void eat() {}

}

class Dog extends Animal {}

class Cat extends Animal {}

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🔹 Constructor Behavior in Inheritance

• When a child class object is created, parent constructor runs first (even if not explicitly written)
• Use super() to call parent constructor manually

java

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class Parent {

    Parent() {

        System.out.println(“Parent constructor”);

    }

}

class Child extends Parent {

    Child() {

        super(); // calls Parent()

        System.out.println(“Child constructor”);

    }

}

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🔹 Method Overriding

When a child class defines a method with the same name and parameters as the parent, it overrides the parent’s method.

java

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class Parent {

    void show() {

        System.out.println(“Parent version”);

    }

}

class Child extends Parent {

    @Override

    void show() {

        System.out.println(“Child version”);

    }

}

📖 Nepali Insight:
Parent ले बनाएको method लाई child ले आफू अनुसार change गर्ने हो — @Override ले भन्न सक्छ “म पुरानो method बदल्दैछु।”

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✅ Rules of Method Overriding

Rule	Must Follow
Same method name	✅
Same number and type of parameters	✅
Must be in parent-child relationship	✅
Cannot reduce visibility (e.g., public → private)	✅
Use @Override annotation	Recommended

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🧪 QA & Automation Use

• Base TestBase class can be extended by all test classes
• Common methods like launchBrowser() go in the parent
• @Override setup or teardown logic in subclasses

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✅ Summary Table

Concept	Description
Inheritance	One class inherits from another
Types	Single, Multilevel, Hierarchical
Constructor	Parent runs first (super() optional)
Method Overriding	Redefining inherited method

📘 Java Topic 9: Polymorphism (Compile-Time vs Run-Time)

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🔹 What is Polymorphism?

Polymorphism means “many forms” — in Java, it allows one method or object to behave differently in different contexts.

📖 Nepali Insight:
Polymorphism भन्नाले एउटै method ले context अनुसार फरक काम गर्नु हो — जस्तै एउटै शब्दले फरक अर्थ दिने जस्तो।

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🔸 Types of Polymorphism in Java

Type	Also Known As	When Happens
Compile-time	Method Overloading	During compilation
Run-time	Method Overriding	During program execution

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✅ 1. Compile-Time Polymorphism (Method Overloading)

When multiple methods in the same class have the same name but different parameters (type, number, or order).

java

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class Calculator {

    int add(int a, int b) {

        return a + b;

    }

    double add(double a, double b) {

        return a + b;

    }

    int add(int a, int b, int c) {

        return a + b + c;

    }

}

📖 Nepali View:
add() method ले parameter अनुसार अलग-अलग काम गर्छ — यो compile time मा decide हुन्छ।

🧠 Compiler checks which method to run based on arguments passed.

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✅ 2. Run-Time Polymorphism (Method Overriding)

When a child class redefines a method of the parent class.

java

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class Animal {

    void sound() {

        System.out.println(“Animal sound”);

    }

}

class Dog extends Animal {

    @Override

    void sound() {

        System.out.println(“Dog barks”);

    }

}

java

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Animal a = new Dog();

a.sound();  // Output: Dog barks

📖 Nepali Insight:
Parent class को reference बाट child को method call हुनु — यो run-time मा decide हुन्छ।

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🔹 Real QA Use of Polymorphism

Scenario	Use
Selenium POM	Base class has click(), overridden in derived pages
API Test Setup	Base request logic overridden in each test case
Framework Reusability	Common logic handled via polymorphic calls

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🔹 Key Differences

Feature	Compile-Time	Run-Time
Also Called	Overloading	Overriding
Resolved At	Compile time	Execution time
Requires Inheritance?	❌ No	✅ Yes
Method Signature	Must be different	Must be same
Example	add(int, int) & add(double, double)	show() overridden in child class

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✅ Summary

Term	Meaning	QA Relevance
Polymorphism	Many forms	Reusable & flexible code
Overloading	Method with same name, diff args	Utility methods
Overriding	Same method redefined in child	Page classes in Selenium

📘 Java Topic 10: Abstraction and Interface

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🔹 What is Abstraction?

Abstraction means showing only the essential details and hiding complex implementation from the user.

📖 Nepali Insight:
Abstraction भन्नाले user लाई काम कस्तो हुन्छ भनेर देखाउने तर भित्र के हुन्छ भन्ने लुकाउने तरिका हो।

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🔹 Why Abstraction?

Purpose	Benefit
Hide complexity	Focus only on what matters
Standardize behavior	Force all child classes to follow structure
Useful in frameworks	Define method structure, implementation later

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✅ 1. Abstract Class

A class declared with the keyword abstract, which can have both abstract (unimplemented) and concrete (implemented) methods.

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🔸 Abstract Class Syntax

java

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abstract class Vehicle {

    abstract void start();  // abstract method

    void fuelType() {

        System.out.println(“Diesel or Petrol”);

    }

}

java

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class Car extends Vehicle {

    void start() {

        System.out.println(“Car starts with key”);

    }

}

📖 Nepali View:
Abstract class मा केही method खाली राखिन्छ, जुन child ले override गर्नैपर्छ।

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✅ 2. Interface

An interface is a completely abstract structure used to define a contract (100% abstract in older versions of Java).

📖 Interface भन्नाले “जो inherit गर्छ उसले यी method हरु बनाउनु पर्छ” भन्ने नियम हो।

---

🔸 Interface Syntax

java

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interface Animal {

    void sound();  // abstract by default

}

class Dog implements Animal {

    public void sound() {

        System.out.println(“Dog barks”);

    }

}

🧠 Key Rule: Class must implement the interface and define all its methods.

---

🔹 Interface vs Abstract Class

Feature	Abstract Class	Interface
Inheritance	extends	implements
Method Types	Abstract + Concrete	Only abstract (until Java 8+)
Variables	Can have instance vars	Only static + final (constants)
Multiple inheritance	❌ Not allowed	✅ Yes (a class can implement multiple interfaces)
Use case	Base class with shared logic	Contract without implementation

---

✅ Real-World QA Example (Interface)

java

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interface WebPage {

    void openPage();

    void validateHeader();

}

java

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class LoginPage implements WebPage {

    public void openPage() { /* logic */ }

    public void validateHeader() { /* logic */ }

}

🧪 Used in:

• Selenium POM frameworks
• API test interfaces (Reusable contracts)

---

✅ Summary

Concept	Use
Abstraction	Hide internal logic, show only function
Abstract Class	Partial implementation + abstraction
Interface	Full abstraction, multi-inheritable
QA Use	Framework design, Page-level contracts, reusable logic

📘 Java Topic 11: Access Modifiers (public, private, protected, and default)

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🔹 What are Access Modifiers?

Access modifiers in Java control the visibility/scope of classes, methods, and variables.

📖 Nepali Insight:
Access modifier भन्नाले code कुन-कुन ठाउँबाट access गर्न मिल्छ भन्ने निर्धारण गर्ने keyword हो।

---

✅ Types of Access Modifiers

Modifier	Accessible Within	Across Packages
public	Anywhere	✅ Yes
private	Only within the same class	❌ No
protected	Same package + subclass outside package	✅ (if inherited)
(default)	Only within the same package	❌ No

---

🔸 1. public

• Can be accessed from anywhere (inside or outside the package)

java

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public class MyClass {

    public int value = 10;

    public void show() {

        System.out.println(“Public method”);

    }

}

📖 Use for: Utility methods, shared constants, Selenium Page Objects.

---

🔸 2. private

• Accessible only within the same class — not visible even to child classes.

java

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public class Secret {

    private String pin = “1234”;

    private void access() {

        System.out.println(“Private method”);

    }

}

📖 Use for: Sensitive data, encapsulation (e.g., private WebElement loginBtn)

---

🔸 3. protected

• Accessible within the same package or subclass in another package.

java

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class Base {

    protected void show() {

        System.out.println(“Protected method”);

    }

}

📖 Used when creating reusable base classes that are extended in other packages.

---

🔸 4. (Default) — No modifier

• When no keyword is used, it’s package-private — only accessible within the same package.

java

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class Helper {

    void helpMe() {

        System.out.println(“Default access”);

    }

}

📖 Used for internal logic or helper classes not intended to be exposed.

---

✅ Summary Table

Modifier	Same Class	Same Package	Subclass (Diff Pkg)	Other Pkg
public	✅	✅	✅	✅
protected	✅	✅	✅	❌
(default)	✅	✅	❌	❌
private	✅	❌	❌	❌

---

🧪 QA & Automation Use

• private WebElement in POM (encapsulation)
• public void clickLogin() for test scripts
• protected WebDriver driver in base class
• Default for internal utility/helper methods

📘 Java Topic 12: static and final Keywords in Java

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🔹 What is the static Keyword?

The static keyword in Java is used to indicate that a method or variable belongs to the class, not to any specific object.

📖 Nepali Insight:
static भन्नाले त्यो variable वा method class सँग सम्बन्धित हुन्छ, object सँग होइन।

---

✅ Use Cases of static

Can Be Applied To	Meaning
static variable	Shared across all objects
static method	Can be called without creating object
static block	Code that runs when class loads
static class	Used in nested class structures

---

🔸 Example: Static Variable

java

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class Student {

    static String schoolName = “Test High School”;

    String studentName;

    Student(String name) {

        studentName = name;

    }

}

java

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System.out.println(Student.schoolName);  // No need for object

🧠 All student objects will share the same school name.

---

🔸 Example: Static Method

java

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class MathUtil {

    static int square(int x) {

        return x * x;

    }

}

java

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System.out.println(MathUtil.square(4));  // Output: 16

📖 Use static methods for utility functions.

---

🔹 What is the final Keyword?

The final keyword is used to restrict modification. Once declared final, you cannot change it, override it, or extend it.

📖 Nepali View:
final भन्नाले अब यो चीज change गर्न मिल्दैन भन्ने हो।

---

✅ Use Cases of final

Final On	Meaning
Variable	Value cannot be changed
Method	Cannot be overridden
Class	Cannot be extended

---

🔸 Final Variable Example

java

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final int MAX_USERS = 100;

✅ You cannot do: MAX_USERS = 200;

---

🔸 Final Method Example

java

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class Parent {

    final void greet() {

        System.out.println(“Hello”);

    }

}

class Child extends Parent {

    // greet() cannot be overridden here

}

---

🔸 Final Class Example

java

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final class Constants {

    static final String APP_NAME = “MyApp”;

}

❌ You cannot extend a final class:

java

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// class MyClass extends Constants → ❌ Error

---

🔹 static vs final

Keyword	Purpose
static	Shared by all, belongs to class
final	Prevent changes (constant, locked)

🧠 You can combine them:

java

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static final String URL = “https://example.com”;

---

✅ QA Framework Usage

Use	Example
Constants	public static final String LOGIN_URL
Common methods	static waitForElement()
Prevent override	Use final in base methods you don’t want changed

---

✅ Summary Table

Keyword	Use	Can Modify?	Belongs To
static	Shared/class-level	✅	Class
final	Locked/constant	❌	Depends on use
static final	Global constant	❌	Class

📘 Java Topic 13: Exception Handling (try-catch-finally, throws, throw, Custom Exceptions)

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🔹 What is Exception Handling?

Exception handling in Java is the process of handling runtime errors so that the program doesn’t crash unexpectedly.

📖 Nepali Insight:
Exception handling भन्नाले program चल्दाखेरी गल्ती आए पनि program रोकिएर नअडोस् भनेर safety mechanism राख्ने हो।

---

✅ Why Use It?

Purpose	Benefit
Handle unexpected errors	Prevent crashes
Maintain flow	Skip only faulty logic, not full program
Show meaningful messages	Guide user or developer

---

🔹 Common Exception Types

Type	Example
ArithmeticException	Division by zero
NullPointerException	Calling method on null object
ArrayIndexOutOfBoundsException	Invalid array index
NumberFormatException	Converting invalid string to number
IOException	File read/write issues

---

✅ 1. try-catch Block

java

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try {

    int result = 10 / 0;

} catch (ArithmeticException e) {

    System.out.println(“Cannot divide by zero”);

}

📖 Nepali View:
Try block मा error आए भने Catch block ले त्यो संभाल्छ।

---

✅ 2. finally Block

• Always executes whether exception occurs or not

java

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try {

    int result = 10 / 2;

} catch (Exception e) {

    System.out.println(“Error”);

} finally {

    System.out.println(“Always runs”);

}

📖 Use it to close database, file, or browser (cleanup code).

---

✅ 3. throw Keyword

Used to manually throw an exception.

java

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throw new ArithmeticException(“Manual error”);

---

✅ 4. throws Keyword

Used in method signature to pass responsibility of exception handling to caller.

java

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public void readFile() throws IOException {

    // file code

}

📖 Nepali: “Yo method चलाउँदा exception आउन सक्छ, सम्भाल्नु तिमीले।” 😄

---

✅ 5. Custom Exception

Create your own exception by extending Exception or RuntimeException.

java

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class AgeException extends Exception {

    AgeException(String message) {

        super(message);

    }

}

class Voter {

    void checkAge(int age) throws AgeException {

        if (age < 18) {

            throw new AgeException(“You are underage”);

        }

    }

}

🧪 Used in test frameworks to handle special validation failures.

---

✅ Summary Table

Keyword	Use
try	Code that may throw error
catch	Handle the error
finally	Always executes
throw	Manually throw exception
throws	Declare exception in method
Custom Exception	Define your own exception type

---

🧪 QA Usage

• Retry on failure (try-catch)
• Gracefully skip test steps if element not found
• Custom error for test validation failure
• API/DB connection handling

📘 Java Topic 14: Collections in Java (List, Set, Map, ArrayList, HashMap)

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🔹 What is the Java Collection Framework?

Java Collections is a framework that provides ready-made data structures like List, Set, Map, etc., to store and manipulate groups of data.

📖 Nepali Insight:
Collection Framework भन्नाले धेरै data लाई सजिलै संगठित गरी राख्न मिल्ने Java को predefined classes को समूह हो।

---

✅ Why Collections?

Need	Example
Store multiple values	All test case IDs
Maintain unique items	Browser names in suite
Store key-value pairs	Username → Password map
Iterate data dynamically	Form input fields, list of results

---

🔹 Key Interfaces in Collection Framework

Interface	Description
List	Ordered, allows duplicates
Set	Unordered, no duplicates
Map	Stores key-value pairs

---

🔸 1. List Interface → ArrayList

java

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import java.util.ArrayList;

ArrayList<String> cities = new ArrayList<>();

cities.add(“Dallas”);

cities.add(“Austin”);

cities.add(“Dallas”);  // Allowed

System.out.println(cities);  // [Dallas, Austin, Dallas]

Feature	Supports
Order preserved	✅
Duplicates	✅
Index access	✅ (e.g., cities.get(0))

---

🔸 2. Set Interface → HashSet

java

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import java.util.HashSet;

HashSet<String> browsers = new HashSet<>();

browsers.add(“Chrome”);

browsers.add(“Firefox”);

browsers.add(“Chrome”);  // Ignored

System.out.println(browsers);  // [Chrome, Firefox]

Feature	Supports
Order preserved	❌
Duplicates	❌

📖 Use Set when you want uniqueness (e.g., environment configs)

---

🔸 3. Map Interface → HashMap

java

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import java.util.HashMap;

HashMap<String, String> credentials = new HashMap<>();

credentials.put(“admin”, “1234”);

credentials.put(“user”, “abcd”);

System.out.println(credentials.get(“admin”));  // Output: 1234

Feature	Supports
Key-value format	✅
Duplicate keys	❌ (replaced if exists)
Values can repeat	✅

📖 Use Map when you need pair-based storage — like locators, usernames, form data, headers.

---

🔹 Iterating Collections

✅ For List or Set:

java

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for (String name : cities) {

    System.out.println(name);

}

✅ For Map:

java

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for (String key : credentials.keySet()) {

    System.out.println(key + ” = ” + credentials.get(key));

}

---

🧪 QA Use Examples

Use Case	Collection
Store list of locators	List<WebElement>
Unique browsers in test	Set<String>
Data-driven testing	Map<String, String> for test data
Multiple test failures	List<String> failedTests

---

✅ Summary Table

Type	Class	Duplicates?	Ordered?	Use Case
List	ArrayList	✅	✅	Test steps, names, inputs
Set	HashSet	❌	❌	Browser list, IDs
Map	HashMap	Key ❌	✅ via LinkedHashMap	Test data, configs

📘 Java Topic 15: Looping with Collections (for-each, Iterator, Lambda)

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🔹 Why Loop Through Collections?

Collections like List, Set, and Map hold multiple data items. Looping allows you to access, verify, or perform actions on each item — useful in both manual and automation testing.

📖 Nepali Insight:
Collection मा भएका सबै items एक-एक गरेर चलाउन loop प्रयोग गरिन्छ — data check, action perform गर्न सजिलो हुन्छ।

---

🔸 1. for-each Loop

Used to iterate through all items in a List, Set, or array.

java

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ArrayList<String> browsers = new ArrayList<>();

browsers.add(“Chrome”);

browsers.add(“Firefox”);

for (String browser : browsers) {

    System.out.println(browser);

}

✅ Best for simple iteration when index isn’t needed.

---

🔸 2. Iterator Interface

Provides controlled access to elements, including the ability to safely remove items while iterating.

java

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import java.util.Iterator;

import java.util.ArrayList;

ArrayList<String> names = new ArrayList<>();

names.add(“Lok”);

names.add(“QA”);

Iterator<String> it = names.iterator();

while (it.hasNext()) {

    System.out.println(it.next());

}

✅ Use it.remove() inside the loop to remove items safely.

📖 Nepali View:
Iterator ले collection मा कुन-कुन item छन् भनेर check गर्दै एक-एक गरेर access गर्न दिन्छ।

---

🔸 3. Looping Through Map

java

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HashMap<String, String> loginData = new HashMap<>();

loginData.put(“admin”, “admin123”);

loginData.put(“user”, “user456”);

for (String key : loginData.keySet()) {

    System.out.println(“Username: ” + key + “, Password: ” + loginData.get(key));

}

✅ Use entrySet() for direct key-value looping:

java

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for (Map.Entry<String, String> entry : loginData.entrySet()) {

    System.out.println(entry.getKey() + ” = ” + entry.getValue());

}

---

🔸 4. Lambda Expressions (Java 8+)

Simplified functional syntax for compact iteration.

java

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browsers.forEach(browser -> System.out.println(browser));

✅ Lambda with Map:

java

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loginData.forEach((key, value) -> System.out.println(key + ” → ” + value));

📖 Nepali View:
Lambda ले code छोट्याउँछ — एकै लाइनमा पूरा काम गर्न सकिन्छ।

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✅ When to Use What?

Situation	Use
Simple list/array	for-each
Need to remove item while looping	Iterator
Key-value pairs	Map.entrySet()
Modern compact syntax	Lambda

---

🧪 QA Use Case Examples

Collection	Example
List<WebElement>	Loop through all buttons on a page
Set<String>	Print all unique browsers used in test
Map<String, String>	Data-driven testing with credentials
Lambda	Report all test result summaries concisely

---

✅ Summary Table

Method	Best For	Syntax Simplicity
for-each	All collections	✅ Easy
Iterator	When modifying/removing	🔁 More control
Lambda	Modern syntax	🔥 Compact and clean
Map.entrySet()	Key-value pairs	✅ Accurate

📘 Java Topic 16: File Handling in Java (Text, Excel, JSON)

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🔹 Why File Handling in QA?

In real-world automation, we often:

• Read test data from external files (text, Excel, JSON)
• Write logs or output results
• Validate file downloads (e.g., from ClaimCenter, policy PDF)

📖 Nepali Insight:
File handling ले तपाईंलाई file बाट data पढ्न, लेख्न र verify गर्न मद्दत गर्छ — जुन testing मा frequently use हुन्छ।

---

🔸 1. Reading and Writing Text Files

✅ Reading a .txt File:

java

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import java.io.*;

BufferedReader reader = new BufferedReader(new FileReader(“testdata.txt”));

String line;

while ((line = reader.readLine()) != null) {

    System.out.println(line);

}

reader.close();

✅ Writing to a .txt File:

java

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BufferedWriter writer = new BufferedWriter(new FileWriter(“result.txt”));

writer.write(“Test Passed”);

writer.newLine();

writer.close();

📌 Used for logging, storing test outputs, reports.

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🔸 2. Excel File Handling (Apache POI)

Used to read/write data from .xls or .xlsx Excel files.
Requires external library: Apache POI

✅ Reading Excel:

java

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import org.apache.poi.ss.usermodel.*;

import java.io.*;

FileInputStream file = new FileInputStream(“data.xlsx”);

Workbook workbook = WorkbookFactory.create(file);

Sheet sheet = workbook.getSheet(“Sheet1”);

String value = sheet.getRow(0).getCell(0).getStringCellValue();

System.out.println(value);

workbook.close();

✅ Writing Excel:

java

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sheet.getRow(0).createCell(1).setCellValue(“Tested”);

FileOutputStream outFile = new FileOutputStream(“data.xlsx”);

workbook.write(outFile);

workbook.close();

📖 Excel is popular for manual + automation hybrid frameworks.

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🔸 3. JSON File Handling (Simple JSON or Jackson)

✅ JSON is widely used in:

• API request/response validation
• Storing config or test data

📘 Reading JSON with org.json.simple:

java

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import org.json.simple.*;

import org.json.simple.parser.*;

FileReader reader = new FileReader(“data.json”);

JSONParser parser = new JSONParser();

JSONObject obj = (JSONObject) parser.parse(reader);

System.out.println(obj.get(“username”));

✅ JSON Example:

json

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{

  “username”: “admin”,

  “password”: “admin123”

}

📌 Jackson and Gson are more advanced options for object mapping.

---

🔹 Exception Handling with Files

Always use:

• try-catch for IOException, ParseException
• finally or try-with-resources to close files

---

✅ Summary Table

File Type	Purpose	Tools
.txt	Logs, simple data	BufferedReader, FileWriter
.xlsx	Structured data	Apache POI
.json	API data/config	JSON.simple, Jackson, Gson

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🧪 QA Use Cases

Scenario	File Type
Export failed test steps	.txt
Store test input for DDT	.xlsx
Validate API payload	.json
Log timestamped test status	.txt, .csv

📘 Java Topic 17: Date and Time (LocalDate, LocalDateTime, Formatting)

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🔹 Why Date and Time in QA?

In test automation, you often:

• Capture execution timestamps
• Validate date fields (e.g., DOB, claim date)
• Generate dynamic future/past dates for input
• Log test activity

📖 Nepali Insight:
Java मा date/time प्रयोग गरेर test timing check, report मा date राख्ने, वा date-based logic validate गर्न सकिन्छ।

---

✅ Java 8 Date-Time API (Modern & Preferred)

The java.time package introduced in Java 8 provides:

• Immutable classes (thread-safe)
• Clear formatting/parsing
• Replaces old Date and Calendar

---

🔸 1. LocalDate – For Date Only

java

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import java.time.LocalDate;

LocalDate today = LocalDate.now();

System.out.println(today);  // 2025-06-23

✅ Create custom date:

java

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LocalDate specific = LocalDate.of(2023, 12, 25);

✅ Add/subtract days:

java

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LocalDate nextWeek = today.plusDays(7);

LocalDate lastMonth = today.minusMonths(1);

---

🔸 2. LocalDateTime – Date + Time

java

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import java.time.LocalDateTime;

LocalDateTime current = LocalDateTime.now();

System.out.println(current);  // 2025-06-23T21:55:30.321

✅ Set custom datetime:

java

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LocalDateTime custom = LocalDateTime.of(2023, 5, 10, 15, 30);

---

🔸 3. Formatting Date-Time

Use DateTimeFormatter to format or parse dates.

java

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import java.time.format.DateTimeFormatter;

DateTimeFormatter format = DateTimeFormatter.ofPattern(“dd-MM-yyyy”);

String formattedDate = today.format(format);

System.out.println(formattedDate);  // 23-06-2025

✅ Full DateTime Example:

java

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DateTimeFormatter fullFormat = DateTimeFormatter.ofPattern(“dd/MM/yyyy HH:mm:ss”);

System.out.println(LocalDateTime.now().format(fullFormat));

---

✅ Parsing a String to Date

java

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String dateStr = “15-08-2024”;

DateTimeFormatter formatter = DateTimeFormatter.ofPattern(“dd-MM-yyyy”);

LocalDate parsedDate = LocalDate.parse(dateStr, formatter);

---

🔹 Common Formats for QA Use

Format String	Output Example	Meaning
“dd-MM-yyyy”	23-06-2025	Day-Month-Year
“yyyy/MM/dd”	2025/06/23	Year first
“HH:mm:ss”	14:35:20	24-hour time
“dd MMM yyyy”	23 Jun 2025	Readable form

---

🧪 QA Use Cases

Use Case	Method
Get current date for report name	LocalDate.now()
Generate future date for policy	plusDays(), plusMonths()
Compare dates in form fields	.isAfter(), .isBefore()
Log test execution time	LocalDateTime.now().format()

---

✅ Summary Table

Class	Use
LocalDate	Date only (no time)
LocalDateTime	Date + time
DateTimeFormatter	Format and parse dates
.plusDays() / .minusDays()	Shift date dynamically
.format()	Convert to readable string

📘 Java Topic 18: Methods (static, instance, parameters, return types)

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🔹 What is a Method?

A method is a block of code that performs a specific task, and can be called whenever needed.

📖 Nepali Insight:
Method भन्नाले code को त्यो block हो जसले एउटा काम गर्न बनाइएको हुन्छ, जसलाई बारम्बार call गर्न सकिन्छ।

---

✅ Why Use Methods?

Benefit	Description
Code reusability	Write once, use many times
Modularity	Break logic into smaller parts
Readability	Easier to understand and maintain
Testing	Test individual methods easily

---

🔹 Method Syntax

java

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returnType methodName(parameters) {

    // method body

    return value; // if returnType ≠ void

}

---

✅ Example 1: Method Without Parameters

java

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public void greet() {

    System.out.println(“Welcome Lok!”);

}

➡ Call it using:

java

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greet();  // if in same class

---

✅ Example 2: Method With Parameters

java

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public void greetUser(String name) {

    System.out.println(“Hello ” + name);

}

➡ Call:

java

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greetUser(“Lok”);

---

✅ Example 3: Method With Return Type

java

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public int add(int a, int b) {

    return a + b;

}

➡ Call:

java

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int result = add(10, 20);

📖 Nepali View:
Method ले value फिर्ता गर्ने हो भने return keyword चाहिन्छ।

---

🔹 Types of Methods in Java

Type	Description	How to Call
Instance Method	Belongs to an object	obj.methodName()
Static Method	Belongs to class	ClassName.methodName()

---

🔸 Instance Method Example

java

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class Calculator {

    int multiply(int x, int y) {

        return x * y;

    }

}

➡ Call it:

java

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Calculator c = new Calculator();

int product = c.multiply(4, 5);

---

🔸 Static Method Example

java

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class Utility {

    static void display() {

        System.out.println(“Static method called”);

    }

}

➡ Call it:

java

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Utility.display();  // No need to create object

📖 Nepali Tip:
static method ले object नचाहिने — direct call गर्न मिल्छ।

---

✅ Return Type Options

Return Type	Example
void	No return value
int, String, boolean	Returns a value of that type
List<String>	Returns a collection
CustomClass	Returns an object

---

🧪 QA Use Case Examples

Use Case	Method Type
Click button	void clickButton()
Get text from page	String getHeaderText()
Add two test data values	int add(int a, int b)
Return API status	boolean isResponseOK()

---

✅ Summary Table

Keyword	Meaning
void	No return value
return	Return result
static	Call without object
Parameters	Inputs to method
Instance	Method tied to object

📘 Java Topic 19: Accessors and Mutators (getters & setters)

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🔹 What Are Accessors and Mutators?

• Accessors are methods used to retrieve (get) the value of a private variable → getX()
• Mutators are methods used to change (set) the value of a private variable → setX(value)

📖 Nepali Insight:
Private variable को value बाहिरबाट access गर्न getter र परिवर्तन गर्न setter method प्रयोग हुन्छ।

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🔹 Why Use Getters and Setters?

Reason	Benefit
Encapsulation	Protect variables from direct access
Validation	Add checks before updating values
Flexibility	You can later change internal logic without changing method call

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🔸 Example

java

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public class Employee {

    private String name;

    private int age;

    // Getter (accessor)

    public String getName() {

        return name;

    }

    // Setter (mutator)

    public void setName(String name) {

        this.name = name;

    }

    // Getter for age

    public int getAge() {

        return age;

    }

    // Setter for age with validation

    public void setAge(int age) {

        if (age > 18) {

            this.age = age;

        }

    }

}

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🔸 How to Use in Main Method

java

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Employee emp = new Employee();

emp.setName(“Lok”);

emp.setAge(30);

System.out.println(emp.getName());  // Lok

System.out.println(emp.getAge());   // 30

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✅ Naming Convention

Method Type	Format
Getter	getVariableName()
Setter	setVariableName(value)

➡ Java uses camelCase: e.g., getFirstName(), setFirstName(“Lok”)

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🔹 Common QA Automation Uses

Purpose	Example
Page Object Model	Set and get input values
Test Data Objects (POJO)	Use getters/setters to access data fields
Data Validation	Add checks inside setters for invalid inputs

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✅ Summary Table

Term	Purpose	Returns
Getter	Access private variable	Value
Setter	Modify private variable	void
Follows	Encapsulation	✅

📖 Nepali View:
Getters ले variable पढ्न मद्दत गर्छ, setters ले value change गर्न दिन्छ, direct access रोक्दछ।

📘 Java Topic 20: Constructor Overloading & Chaining (this() and super() usage)

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🔹 What is a Constructor?

A constructor is a special method that is automatically called when an object is created.
Its purpose is to initialize variables or prepare the object.

📖 Nepali Insight:
Constructor भनेको class को object बनाउँदा साथै चल्ने method हो — जुन automatically run हुन्छ।

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✅ Types of Constructors

Type	Description
Default Constructor	No parameters
Parameterized Constructor	Takes arguments to initialize fields

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🔸 Example:

java

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class Person {

    String name;

    int age;

    // Default Constructor

    Person() {

        name = “Unknown”;

        age = 0;

    }

    // Parameterized Constructor

    Person(String name, int age) {

        this.name = name;

        this.age = age;

    }

}

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🔹 What is Constructor Overloading?

Having multiple constructors in the same class with different parameter lists.

📖 Nepali View:
Constructor को version फरक फरक बनाउनु — ताकि object बनाउन flexible तरीका होस्।

java

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class Book {

    Book() {

        System.out.println(“Default Book”);

    }

    Book(String title) {

        System.out.println(“Book title: ” + title);

    }

    Book(String title, int pages) {

        System.out.println(“Book: ” + title + “, Pages: ” + pages);

    }

}

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🔹 What is Constructor Chaining?

Calling one constructor from another constructor using:

• this() – Call another constructor in same class
• super() – Call constructor from parent class

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✅ Using this()

java

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class Student {

    String name;

    int age;

    Student() {

        this(“Lok”, 25);  // Calls another constructor

    }

    Student(String name, int age) {

        this.name = name;

        this.age = age;

    }

}

📖 Nepali Tip:
this() ले यही class को अर्को constructor call गर्छ।

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✅ Using super()

java

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class Animal {

    Animal() {

        System.out.println(“Animal constructor”);

    }

}

class Dog extends Animal {

    Dog() {

        super();  // Call parent class constructor

        System.out.println(“Dog constructor”);

    }

}

📖 super() ले parent class को constructor call गर्छ।

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✅ Rules

Rule	Detail
this() must be the first line in constructor	✅
super() must also be first (you can’t use both together)	✅
Use this() to reduce duplicate code	✅
Only constructors can call this() and super()	✅

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🧪 QA Use Case

Use Case	Example
Framework utility class	Overloaded constructors for different test data
Base test class	super() to reuse parent setup logic
POM structure	this() for field initialization in multiple forms

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✅ Summary Table

Concept	Meaning	Example
Constructor Overloading	Multiple constructors	Book(String) and Book()
Constructor Chaining	Call one constructor from another	this(), super()
this()	Same class constructor	this(“Lok”, 25);
super()	Parent class constructor	super();

🔹 1. Prime Number Check

A prime number is only divisible by 1 and itself (e.g., 2, 3, 5, 7…).

📖 Nepali Insight:
Prime number भन्नाले जसलाई 1 र आफू बाहेक अरु कुनै संख्याले divide गर्न सकिँदैन।

✅ Java Code:

java

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int num = 7;

boolean isPrime = true;

if (num <= 1) isPrime = false;

else {

    for (int i = 2; i < num; i++) {

        if (num % i == 0) {

            isPrime = false;

            break;

        }

    }

}

System.out.println(isPrime ? “Prime” : “Not Prime”);

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🔹 2. Palindrome Check

A palindrome is a word/number that reads the same forward and backward (e.g., “121”, “madam”).

📖 Nepali:
Palindrome भनेको अगाडिबाट पढ्दा र पछाडिबाट पढ्दा एउटै देखिने number/string हो।

✅ Java Code (number):

java

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int num = 121, reversed = 0, original = num;

while (num != 0) {

    int digit = num % 10;

    reversed = reversed * 10 + digit;

    num /= 10;

}

System.out.println(original == reversed ? “Palindrome” : “Not Palindrome”);

✅ Java Code (string):

java

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String str = “madam”;

String reversed = new StringBuilder(str).reverse().toString();

System.out.println(str.equals(reversed) ? “Palindrome” : “Not Palindrome”);

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🔹 3. Odd or Even Check

📖 Nepali:
Even number ले 2 ले divide हुँदा remainder दिँदैन (0), Odd ले दिन्छ (1)।

✅ Java Code:

java

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int num = 7;

if (num % 2 == 0) {

    System.out.println(“Even”);

} else {

    System.out.println(“Odd”);

}

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🔹 4. Difference: final, finally, finalize

Keyword	Type	Purpose	Example
final	Keyword	Prevent change (variable, method, class)	final int x = 10;
finally	Block	Runs after try-catch regardless	Cleanup code
finalize()	Method	Called before object is garbage collected	Rarely used now

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✅ Example: final

java

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final int speed = 100;

// speed = 200; // ❌ Error: can’t change

✅ Example: finally

java

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try {

    int result = 10 / 2;

} catch (Exception e) {

    System.out.println(“Error”);

} finally {

    System.out.println(“Always executes”);

}

✅ Example: finalize() (not recommended in modern Java)

java

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protected void finalize() {

    System.out.println(“Object is garbage collected”);

}

📖 Nepali Tip:

• final = change गर्न नपाइने
• finally = सधैं चल्ने block
• finalize() = JVM ले object हटाउनु अघि call गर्ने method

📘 Java Logic Practice – Factorial, Fibonacci, Reverse String & Number

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🔹 1. Factorial of a Number

The factorial of a number n is n × (n-1) × (n-2)…× 1

📖 Nepali Insight:
Factorial भन्नाले कुनै पनि संख्या n को सबैभन्दा सानो सम्म गुणन हो।
E.g., 5! = 5×4×3×2×1 = 120

✅ Java Code:

java

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int n = 5;

int fact = 1;

for (int i = 1; i <= n; i++) {

    fact *= i;

}

System.out.println(“Factorial: ” + fact);  // Output: 120

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🔹 2. Fibonacci Series

Fibonacci series: 0, 1, 1, 2, 3, 5, 8,…
Each number = sum of previous two

📖 Nepali View:
यो series मा अर्को संख्या पहिला दुईको योग हो।

✅ Java Code:

java

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int n = 10;

int a = 0, b = 1;

System.out.print(“Fibonacci: ” + a + ” ” + b + ” “);

for (int i = 2; i < n; i++) {

    int c = a + b;

    System.out.print(c + ” “);

    a = b;

    b = c;

}

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🔹 3. Reverse a Number

📖 Nepali:
संख्या उल्ट्याउने — 123 becomes 321

✅ Java Code:

java

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int num = 123;

int reversed = 0;

while (num != 0) {

    int digit = num % 10;

    reversed = reversed * 10 + digit;

    num /= 10;

}

System.out.println(“Reversed: ” + reversed);

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🔹 4. Reverse a String

📖 Nepali:
String लाई पछाडिबाट अगाडि बनाउने।

✅ Java Code:

java

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String str = “Lok”;

String reversed = “”;

for (int i = str.length() – 1; i >= 0; i–) {

    reversed += str.charAt(i);

}

System.out.println(“Reversed String: ” + reversed);  // koL

✅ Or use:

java

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String reversed = new StringBuilder(str).reverse().toString();

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✅ Summary Table

Logic	Input	Output
Factorial	5	120
Fibonacci	10 terms	0 1 1 2 3 5 8 13 21 34
Reverse Number	1234	4321
Reverse String	“Test”	“tseT”

📘 Java Logic Practice – Part 2 (Armstrong, Swap, Prime in Range)

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🔹 1. Armstrong Number

A number is called Armstrong if the sum of its digits raised to the power of number of digits equals the original number.

📖 Nepali Insight:
153 = 1³ + 5³ + 3³ = 1 + 125 + 27 = 153 → Armstrong number हो।

✅ Java Code:

java

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int num = 153, original = num;

int result = 0;

while (num != 0) {

    int digit = num % 10;

    result += Math.pow(digit, 3);

    num /= 10;

}

System.out.println(result == original ? “Armstrong” : “Not Armstrong”);

📌 Use Math.pow(digit, numberOfDigits) for any length number.

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🔹 2. Swap Two Numbers Without Temp Variable

📖 Nepali View:
दुई संख्यालाई एक अर्कासँग third variable प्रयोग नगरी साट्ने।

✅ Java Code:

java

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int a = 5, b = 10;

a = a + b;  // 15

b = a – b;  // 5

a = a – b;  // 10

System.out.println(“a: ” + a + “, b: ” + b);

✅ Output:

makefile

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a: 10

b: 5

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🔹 3. Prime Numbers in a Range (e.g., 1 to 50)

📖 Nepali Insight:
1 देखि 50 भित्रका सबै Prime संख्या छान्ने।

✅ Java Code:

java

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for (int i = 2; i <= 50; i++) {

    boolean isPrime = true;

    for (int j = 2; j <= i / 2; j++) {

        if (i % j == 0) {

            isPrime = false;

            break;

        }

    }

    if (isPrime) {

        System.out.print(i + ” “);

    }

}

✅ Output:

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2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

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✅ Bonus Logic (Extra Fast)

🔸 Check Even Digits in a Number

java

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int num = 2468;

boolean allEven = true;

while (num != 0) {

    int digit = num % 10;

    if (digit % 2 != 0) {

        allEven = false;

        break;

    }

    num /= 10;

}

System.out.println(allEven ? “All even digits” : “Not all even”);

🔸 Count Digits in a Number

java

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int num = 987654;

int count = 0;

while (num != 0) {

    count++;

    num /= 10;

}

System.out.println(“Digits: ” + count);

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✅ Summary Table

Task	Example Input	Output
Armstrong	153	Armstrong
Swap	a=5, b=10	a=10, b=5
Prime in range	1–50	List of primes
Even digit check	2468	All even
Digit count	987654	6