java中的匿名内部类总结

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