Java

• 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.

🔸 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.

🔸 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

java

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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

}

🔸 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.

🔹 Class vs Object

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”;

    }

}

✅ Summary Table

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

🔹 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”);

    }

}

🔹 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.

🔹 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।

✅ Types of Constructors

java

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class Person {

    String name;

    // Constructor

    Person(String personName) {

        name = personName;

    }

    void greet() {

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

    }

}

🔹 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।

🔹 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।”

✅ Summary Table

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

🔹 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।

✅ Why Use Inheritance?

✅ 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

🔹 Types of Inheritance in Java

🔸 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”); }

}

🔸 Multilevel Inheritance

java

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class Animal {

    void eat() {}

}

class Dog extends Animal {

    void bark() {}

}

class Puppy extends Dog {

    void weep() {}

}

🔸 Hierarchical Inheritance

java

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class Animal {

    void eat() {}

}

class Dog extends Animal {}

class Cat extends Animal {}

🔹 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”);

    }

}

🔹 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।”

✅ Rules of Method Overriding

🧪 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

✅ Summary Table

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

🔹 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।

🔸 Types of Polymorphism in Java

✅ 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.

✅ 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।

🔹 Real QA Use of Polymorphism

🔹 Key Differences

✅ Summary

📘 Java Topic 10: Abstraction and Interface

🔹 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।

🔹 Why Abstraction?

✅ 1. Abstract Class

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

🔸 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।

✅ 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

✅ 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

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

🔹 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

🔸 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

🧪 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

🔹 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

🔸 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 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

🧠 You can combine them:

java

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

✅ QA Framework Usage

✅ Summary Table

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

🔹 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?

🔹 Common Exception Types

✅ 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

🧪 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)

🔹 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?

🔹 Key Interfaces in Collection Framework

🔸 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]

🔸 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]

📖 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

📖 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

✅ Summary Table

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

🔹 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।

✅ When to Use What?

🧪 QA Use Case Examples

✅ Summary Table

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

🔹 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.

🔸 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.

🔸 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

🧪 QA Use Cases

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

🔹 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:

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

✅ Add/subtract days:

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LocalDate nextWeek = today.plusDays(7);

LocalDate lastMonth = today.minusMonths(1);

🔸 2. LocalDateTime – Date + Time

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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:

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

🔸 3. Formatting Date-Time

Use DateTimeFormatter to format or parse dates.

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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:

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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

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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

🧪 QA Use Cases

✅ Summary Table

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

🔹 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?

🔹 Method Syntax

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returnType methodName(parameters) {

    // method body

    return value; // if returnType ≠ void

}

✅ Example 1: Method Without Parameters

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public void greet() {

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

}

➡ Call it using:

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greet();  // if in same class

✅ Example 2: Method With Parameters

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public void greetUser(String name) {

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

}

➡ Call:

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greetUser(“Lok”);

✅ Example 3: Method With Return Type

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public int add(int a, int b) {

    return a + b;

}

➡ Call:

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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

🔸 Instance Method Example

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class Calculator {

    int multiply(int x, int y) {

        return x * y;

    }

}

➡ Call it:

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Calculator c = new Calculator();

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

🔸 Static Method Example

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class Utility {

    static void display() {

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

    }

}

➡ Call it:

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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

🧪 QA Use Case Examples

✅ Summary Table

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

🔹 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।

🔹 Why Use Getters and Setters?

🔸 Example

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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;

        }

    }

}

🔸 How to Use in Main Method

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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

✅ Naming Convention

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

🔹 Common QA Automation Uses

✅ Summary Table

📖 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)

🔹 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।

✅ Types of Constructors

🔸 Example:

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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;

    }

}

🔹 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।

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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);

    }

}

🔹 What is Constructor Chaining?

Calling one constructor from another constructor using:

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

✅ Using this()

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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।

✅ Using super()

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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।

✅ Rules

🧪 QA Use Case

✅ Summary Table

🔹 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:

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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”);

🔹 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):

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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):

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String str = “madam”;

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

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

🔹 3. Odd or Even Check

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

✅ Java Code:

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int num = 7;

if (num % 2 == 0) {

    System.out.println(“Even”);

} else {

    System.out.println(“Odd”);

}

🔹 4. Difference: final, finally, finalize

✅ Example: final

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final int speed = 100;

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

✅ Example: finally

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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)

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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

🔹 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:

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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

🔹 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:

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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;

}

🔹 3. Reverse a Number

📖 Nepali:
संख्या उल्ट्याउने — 123 becomes 321

✅ Java Code:

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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);

🔹 4. Reverse a String

📖 Nepali:
String लाई पछाडिबाट अगाडि बनाउने।

✅ Java Code:

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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:

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

✅ Summary Table

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

🔹 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:

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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.

🔹 2. Swap Two Numbers Without Temp Variable

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

✅ Java Code:

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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:

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a: 10

b: 5

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

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

✅ Java Code:

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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

✅ Bonus Logic (Extra Fast)

🔸 Check Even Digits in a Number

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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

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int num = 987654;

int count = 0;

while (num != 0) {

    count++;

    num /= 10;

}

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

✅ Summary Table