Java class Keyword

The class keyword in Java is used to create a class, which is a blueprint for objects. A class defines the properties and behaviors that objects created from the class will have.

Table of Contents

1. Introduction
2. class Keyword Syntax
3. Understanding Classes
4. Examples
   • Basic Class Declaration
   • Creating Objects from a Class
   • Class with Methods
   • Class with Constructors
5. Real-World Use Case
6. Conclusion

Introduction

The class keyword is fundamental in Java programming. It is used to define new data types by grouping variables and methods into a single unit.

class Keyword Syntax

The syntax for declaring a class is as follows:

class ClassName {
    // fields (variables)
    // methods
}

Example:

class Car {
    String color;
    String model;
    void drive() {
        System.out.println("The car is driving.");
    }
}

Understanding Classes

A class is a template for creating objects. It contains fields (variables) to hold data and methods to define behaviors.

Key Points:

• Fields (Variables): Store the state or attributes of an object.
• Methods: Define actions that an object can perform.
• Constructors: Special methods to initialize objects.

Examples

Basic Class Declaration

Let’s start with a simple class called Car.

Example

class Car {
    String color;
    String model;

    void drive() {
        System.out.println("The car is driving.");
    }
}

Creating Objects from a Class

You can create objects from a class using the new keyword.

Example

public class Main {
    public static void main(String[] args) {
        Car myCar = new Car();
        myCar.color = "Red";
        myCar.model = "Toyota";
        System.out.println("Car model: " + myCar.model);
        myCar.drive();
    }
}

Output:

Compilation failed.

Class with Methods

A class can contain multiple methods to define various behaviors.

Example

class Calculator {
    int add(int a, int b) {
        return a + b;
    }

    int subtract(int a, int b) {
        return a - b;
    }
}

public class Main {
    public static void main(String[] args) {
        Calculator calc = new Calculator();
        System.out.println("Sum: " + calc.add(10, 5));
        System.out.println("Difference: " + calc.subtract(10, 5));
    }
}

Output:

Sum: 15
Difference: 5

Class with Constructors

Constructors are special methods used to initialize objects. They have the same name as the class and no return type.

Example

class Person {
    String name;
    int age;

    // Constructor
    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    void display() {
        System.out.println("Name: " + name + ", Age: " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        Person person = new Person("Alice", 30);
        person.display();
    }
}

Output:

Name: Alice, Age: 30

Real-World Use Case

Creating a Student Class

In real-world applications, you might create classes to represent entities like students, employees, or products.

Example

class Student {
    String name;
    int id;

    // Constructor
    Student(String name, int id) {
        this.name = name;
        this.id = id;
    }

    void study() {
        System.out.println(name + " is studying.");
    }
}

public class Main {
    public static void main(String[] args) {
        Student student = new Student("John", 123);
        System.out.println("Student ID: " + student.id);
        student.study();
    }
}

Output:

Student ID: 123
John is studying.

Conclusion

The class keyword in Java is used to create classes, which are blueprints for objects. By defining fields and methods in a class, you can create objects that have specific properties and behaviors. Understanding how to use classes is fundamental to Java programming and helps in organizing and managing code efficiently.