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匿名內部類也就是沒有名字的內部類

正因為沒有名字，所以匿名內部類只能使用一次，它通常用來簡化代碼編寫

但使用匿名內部類還有個前提條件：必須繼承一個父類或實現一個接口

實例1:不使用匿名內部類來實現抽象方法

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(); 
               } 
        }

運行結果：eat something

可以看到，我們用Child繼承了Person類，然后實現了Child的一個實例，將其向上轉型為Person類的引用

但是，如果此處的Child類只使用一次，那么將其編寫為獨立的一個類豈不是很麻煩？

這個時候就引入了匿名內部類

實例2：匿名內部類的基本實現

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(); 
                } 
        }

運行結果：eat something

可以看到，我們直接將抽象類Person中的方法在大括號中實現了

這樣便可以省略一個類的書寫

并且，匿名內部類還能用于接口上

實例3：在接口上使用匿名內部類

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(); 
                } 
        }

運行結果：eat something

由上面的例子可以看出，只要一個類是抽象的或是一個接口，那么其子類中的方法都可以使用匿名內部類來實現

常用的情況就是在多線程的實現上，因為要實現多線程必須繼承Thread類或是繼承Runnable接口

實例4：Thread類的匿名內部類實現

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(); 
                } 
        }

運行結果：1 2 3 4 5

實例5：Runnable接口的匿名內部類實現

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(); 
                } 
        }

運行結果：1 2 3 4 5