匿名内部类也就是没有名字的内部类

正因为没有名字，所以匿名内部类只能使用一次，它通常用来简化代码编写

但使用匿名内部类还有个前提条件：必须继承一个父类或实现一个接口

实例1:不使用匿名内部类来实现抽象方法

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();
               }
        }

运行结果：eat something

可以看到，我们用Child继承了Person类，然后实现了Child的一个实例，将其向上转型为Person类的引用

但是，如果此处的Child类只使用一次，那么将其编写为独立的一个类岂不是很麻烦？

这个时候就引入了匿名内部类

实例2：匿名内部类的基本实现

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();
                }
        }

运行结果：eat something

可以看到，我们直接将抽象类Person中的方法在大括号中实现了

这样便可以省略一个类的书写

并且，匿名内部类还能用于接口上

实例3：在接口上使用匿名内部类

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();
                }
        }

运行结果：eat something

由上面的例子可以看出，只要一个类是抽象的或是一个接口，那么其子类中的方法都可以使用匿名内部类来实现

常用的情况就是在多线程的实现上，因为要实现多线程必须继承Thread类或是继承Runnable接口

实例4：Thread类的匿名内部类实现

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();
                }
        }

运行结果：1 2 3 4 5

实例5：Runnable接口的匿名内部类实现

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();
                }
        }

运行结果：1 2 3 4 5