How to call Java class?

How to Call a Java Class

Introduction

In Java, a class is a blueprint or a template that defines the structure and behavior of an object. It is a fundamental concept in object-oriented programming (OOP) and is used to create complex objects that can interact with each other. When you want to call a Java class, you need to use the correct syntax and follow the correct steps. In this article, we will guide you through the process of calling a Java class.

Syntax

The syntax to call a Java class is as follows:

class ClassName {

    // class body

}

• class ClassName: This is the keyword to define a new class.
• ClassName: This is the name of the class.
• // class body: This is the body of the class, where you can define methods, variables, and other class-related code.

Calling a Java Class

To call a Java class, you need to use the new keyword followed by the class name. Here’s an example:

public class Main {

    public static void main(String[] args) {

        // Create an instance of the class

        MyClass obj = new MyClass();



        // Call a method on the object

        obj.myMethod();

    }

}

• public class Main: This is the main class where the main method is defined.
• public static void main(String[] args): This is the main method where the program starts execution.
• MyClass: This is the class where the myMethod method is defined.
• obj = new MyClass();: This line creates an instance of the MyClass class.
• obj.myMethod();: This line calls the myMethod method on the obj object.

Access Modifiers

Java classes can have different access modifiers, which determine how the class can be accessed from other classes. Here are the common access modifiers:

• public: This access modifier means that the class can be accessed from any other class.
• private: This access modifier means that the class can only be accessed from the same class.
• protected: This access modifier means that the class can be accessed from the same class and any subclass of the class.

Constructors

Constructors are special methods that are used to initialize objects when they are created. Here’s an example:

public class Person {

    private String name;

    private int age;



    public Person(String name, int age) {

        this.name = name;

        this.age = age;

    }



    public void displayInfo() {

        System.out.println("Name: " + name + ", Age: " + age);

    }

}

• public class Person: This is the class where the Person constructor is defined.
• private String name;: This is the variable that is used to store the person’s name.
• private int age;: This is the variable that is used to store the person’s age.
• public Person(String name, int age): This is the constructor where the name and age variables are initialized.
• this.name = name;: This line assigns the name variable to the this keyword.
• this.age = age;: This line assigns the age variable to the this keyword.

Methods

Methods are functions that are used to perform specific tasks. Here’s an example:

public class Calculator {

    public int add(int a, int b) {

        return a + b;

    }



    public int subtract(int a, int b) {

        return a - b;

    }

}

• public class Calculator: This is the class where the Calculator method is defined.
• public int add(int a, int b): This is the method where the add function is defined.
• public int subtract(int a, int b): This is the method where the subtract function is defined.

Inheritance

Inheritance is a mechanism that allows one class to inherit the properties and behavior of another class. Here’s an example:

public class Animal {

    private String name;



    public Animal(String name) {

        this.name = name;

    }



    public void sound() {

        System.out.println("The animal makes a sound.");

    }

}



public class Dog extends Animal {

    public Dog(String name) {

        super(name);

    }



    public void bark() {

        System.out.println("The dog barks.");

    }

}

• public class Animal: This is the class where the Animal constructor is defined.
• public String name;: This is the variable that is used to store the animal’s name.
• public void sound(): This is the method where the animal makes a sound.
• public class Dog: This is the class where the Dog constructor is defined.
• public Dog(String name): This is the constructor where the name variable is initialized.
• super(name);: This line calls the Animal constructor with the name variable.
• public void bark(): This is the method where the dog barks.

Conclusion

In conclusion, calling a Java class is a straightforward process that involves using the new keyword followed by the class name. The class can have different access modifiers, constructors, methods, and inheritance. By understanding these concepts, you can write more efficient and effective Java programs.

Table: Access Modifiers

Access Modifier	Description
public	Can be accessed from any other class
private	Can only be accessed from the same class
protected	Can be accessed from the same class and any subclass of the class

Table: Constructors

Constructor	Description
public constructor	Initializes an object with the given parameters
private constructor	Initializes an object with the given parameters and no parameters
protected constructor	Initializes an object with the given parameters and no parameters

Table: Methods

Method	Description
public method	Can be accessed from any other class
private method	Can only be accessed from the same class
protected method	Can be accessed from the same class and any subclass of the class

Table: Inheritance

Inheritance	Description
public class Animal	Extends the Animal class
public class Dog extends Animal	Extends the Animal class and adds new properties and behavior