Java Anonymous Classes

In this tutorial, you will learn about anonymous classes in Java through examples.

In Java, a class can contain another class called a nested class. A nested class can be created without providing any name.

A nested class without any name is called an anonymous class.

An anonymous class must be defined within another class. Therefore, it is also called an anonymous inner class. Its syntax is:

class outerClass {
　　　　//Define an anonymous class
　　　　object1　= new Type(parameterList) {
　　　　　　　　　//The body of the anonymous class
　　　　};
}

An anonymous class usually inherits a subclass or implements an interface.

Here,Type(Type)Can be

1. The superclass inherited by the anonymous class

2. The interface implemented by the anonymous class

The above code creates an object of the anonymous class at runtime1.

Note:An anonymous class is defined within an expression. Therefore, a semicolon is used at the end of the anonymous class to indicate the end of the expression.

Example1An anonymous inner class inherits the class

class Polygon {
　　　public void display() {
　　　　　　System.out.println("Inside the Polygon class");
　　　}
}
class AnonymousDemo {
　　　public void createClass() {
　　　　　　//Create an anonymous class, inheriting the class Polygon
　　　　　　Polygon p1　= new Polygon() {
　　　　　　　　　public void display() {
　　　　　　　　　　　　System.out.println("The internal of the anonymous class.");
　　　　　　　　　}
　　　　　　};
　　　　　　p1.display();
　　　}
}
class Main {
　　　public static void main(String[] args) {
　　　　　　　AnonymousDemo an = new AnonymousDemo();
　　　　　　　an.createClass();
　　　}
}

Output result

The internal of the anonymous class

In the above example, we created a class Polygon. It has only one method display().

Then, we created an anonymous class that inherits the class Polygon and overrides the display() method.

When we run this program, an object of the anonymous class p will be created1. Then, the object calls the display() method of the anonymous class.

Example2An anonymous class that implements the interface

interface Polygon {
　　　public void display();
}
class AnonymousDemo {
　　　public void createClass() {
　　　　　　//Implementation of the interface by an anonymous class
　　　　　　Polygon p1　= new Polygon() {
　　　　　　　　　public void display() {
　　　　　　　　　　　　System.out.println("The internal of the anonymous class.");
　　　　　　　　　}
　　　　　　};
　　　　　　p1.display();
　　　}
}
class Main {
　　　public static void main(String[] args) {
　　　　　　AnonymousDemo an = new AnonymousDemo();
　　　　　　an.createClass();
　　　}
}

Output result

The internal of the anonymous class

In the above example, we created an anonymous class that implements the Polygon interface.

Advantages of anonymous classes

In the anonymous class, create objects as needed. That is, create objects to perform certain specific tasks. For example,

Object = new Example() {
　　　public void display() {
　　　　　　System.out.println("Anonymous class overrides the display() method.");
　　　}
};

Here, when we need to override the display() method, an object of the anonymous class will be dynamically created.

Anonymous classes also help us make the code concise.