This article mainly introduces the relevant information on the summary of anonymous internal classes in java. I hope this article can help everyone. Friends in need can refer to
Summary of anonymous internal classes in java
Anonymous inner classes are inner classes without names
Because they have no names, anonymous inner classes can only be used once. They are usually used to simplify code writing
But there is a prerequisite for using anonymous inner classes: you must inherit a parent class or implement an interface
Example 1: Do not use anonymous inner classes to implement abstract methods
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(); } }
Running result: eat something
As you can see, we use Child to inherit the Person class, and then implement a Child instance, upcast it into a reference to the Person class
However, if the Child class here is only used once, wouldn't it be troublesome to write it as an independent class?
At this time, anonymous inner classes were introduced
Example 2: Basic implementation of anonymous inner classes
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(); } }
Run results: eat something
As you can see, we directly implemented the methods in the abstract class Person in braces
This way, we can omit the method of a class Writing
And, anonymous inner classes can also be used on interfaces
Example 3: Using anonymous inner classes on interfaces
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(); } }
Run result: eat something
As can be seen from the above example, as long as a class is abstract or an interface, then in its subclass All methods can be implemented using anonymous inner classes
The most common situation is in the implementation of multi-threading, because to implement multi-threading you must inherit the Thread class or inherit the Runnable interface
Example 4: Anonymous inner class implementation of 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(); } }
Running result: 1 2 3 4 5
Example 5: Anonymous inner class implementation of Runnable interface
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(); } }
Running results: 1 2 3 4 5
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