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.