Java | Introduction to OOP concepts (classes, objects, methods, encapsulation, inheritance, and polymorphism)

Java is a popular programming language that is used to build a variety of applications, from web-based applications to mobile apps. One of the reasons for its popularity is that it is an object-oriented programming (OOP) language. In this article, we will introduce the basic OOP concepts in Java, including classes, objects, methods, encapsulation, inheritance, and polymorphism.

Classes:

In Java, a class is a blueprint or template for creating objects. A class defines the properties and behaviors that objects of that class will have. Here’s an example of a simple class:

public class MyClass {
    int myProperty;
    public void myMethod() {
        System.out.println("Hello, world!");
    }
}

In this example, we define a class called MyClass that has a property called myProperty and a method called myMethod. The public keyword means that other classes can access these members.

Objects:

An object is an instance of a class. You can create as many objects as you need from a single class. Here’s an example of how to create an object of the MyClass class:

MyClass myObject = new MyClass();

In this example, we create a new object of the MyClass class and assign it to a variable called myObject.

Methods:

A method is a block of code that performs a specific task. In Java, methods are defined inside classes. Here’s an example of a method that takes a parameter:

public class MyClass {
    public void printMessage(String message) {
        System.out.println(message);
    }
}

In this example, we define a method called printMessage that takes a String parameter called message. The method prints the value of the message parameter to the console.

Encapsulation:

Encapsulation is the process of hiding the implementation details of a class from other classes. It allows you to protect the internal state of an object from being modified by other classes. In Java, you can use access modifiers to control access to the members of a class. Here’s an example of a class with private properties and a public method:

public class MyClass {
    private int myPrivateProperty;

    public void setMyPrivateProperty(int value) {
        myPrivateProperty = value;
    }

    public int getMyPrivateProperty() {
        return myPrivateProperty;
    }
}

In this example, we define a class called MyClass that has a private property called myPrivateProperty. We also define two public methods, setMyPrivateProperty and getMyPrivateProperty, that allow other classes to set and get the value of the myPrivateProperty property.

Inheritance:

Inheritance is the process of creating a new class from an existing class. The new class, called a subclass, inherits the properties and behaviors of the existing class, called the superclass. In Java, you can use the extends keyword to create a subclass. Here’s an example of a subclass that extends the MyClass class:

public class MySubclass extends MyClass {
    public void mySubclassMethod() {
        System.out.println("This is a subclass method!");
    }
}

In this example, we define a subclass called MySubclass that extends the MyClass class. The MySubclass class has a method called mySubclassMethod that is not present in the MyClass class.

Polymorphism:

Polymorphism is the ability of an object to take on many forms. In Java, polymorphism is achieved through method overriding and method overloading. Method overriding occurs when a subclass provides

an implementation for a method that is already defined in its superclass. Method overloading occurs when a class has multiple methods with the same name but different parameters. Here’s an example of method overriding and method overloading:

public class MyClass {
    public void myMethod() {
        System.out.println("This is the superclass method!");
    }

    public void myMethod(String message) {
        System.out.println(message);
    }
}

public class MySubclass extends MyClass {
    @Override
    public void myMethod() {
        System.out.println("This is the subclass method!");
    }

    public void myMethod(int value) {
        System.out.println("The value is: " + value);
    }
}

In this example, we define a superclass called MyClass that has two methods, myMethod and myMethod with a String parameter. We also define a subclass called MySubclass that overrides the myMethod method and adds a new method called myMethod with an int parameter.

To summarize, Java is an object-oriented programming language that provides a number of OOP concepts such as classes, objects, methods, encapsulation, inheritance, and polymorphism. By using these concepts, you can create well-structured and maintainable code.