Anonymous inner class summary in Java

Anonymous inner class is also an inner class without a name

Because there is no name, the anonymous inner class can only be used once, and it is often used to simplify code writing

But there is also a precondition for using anonymous inner classes: You must inherit from a parent class or implement an interface

Example 1: Do not use anonymous inner classes to implement abstract methods?

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abstract class Person {    public abstract void eat();}class Child extends Person {    public void eat() {        System.out.println("eat something");    }}public class Demo {    public static void main(String[] args) {        Person p = new Child();        p.eat();    }}

Operation Result: Eat something

As you can see, we inherit the person class with child, and then we implement an instance of child and transform it upward into a reference to the person class.

However, if the child class here is used only once, wouldn't it be a hassle to write it as a separate class?

The anonymous inner class is introduced at this time.

Example 2: The basic implementation of an anonymous inner class?

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abstract class Person {    public abstract void eat();}public class Demo {    public static void main(String[] args) {        Person p = new Person() {            public void eat() {                System.out.println("eat something");            }        };        p.eat();    }}

Operation Result: Eat something

As you can see, we directly implement the methods in the abstract class person in curly braces.

This allows you to omit the writing of a class

Also, anonymous inner classes can be used on interfaces

Example 3: Use an anonymous inner class on an interface?

interface Person {    public void eat();}public class Demo {    public static void main(String[] args) {        Person p = new Person() {            public void eat() {                System.out.println("eat something");            }        };        p.eat();    }}

Operation Result: Eat something

As can be seen from the above example, as long as a class is abstract or an interface, the methods in its subclasses can be implemented using anonymous inner classes

The most common situation is in the implementation of multithreading, because to implement multithreading must inherit the thread class or inherit the Runnable interface

Example of an anonymous inner class implementation of the 4:thread class?

public class Demo {    public static void main(String[] args) {        Thread t = new Thread() {            public void run() {                for (int i = 1; i <= 5; i++) {                    System.out.print(i + " ");                }            }        };        t.start();    }}

Operation Result: 1 2 3) 4 5

An anonymous inner class implementation of the instance 5:runnable interface?

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public class Demo {    public static void main(String[] args) {        Runnable r = new Runnable() {            public void run() {                for (int i = 1; i <= 5; i++) {                    System.out.print(i + " ");                }            }        };        Thread t = new Thread(r);        t.start();    }}

Operation Result: 1 2 3) 4 5

Anonymous inner class summary in Java