java-接口回调

编程技术  /  houtizong 发布于 3年前   65

/* * Java里面的接口回调，最简单的情况示意如下 */interface A {}class B implements A {}class C implements A {}class Test {    A b = new B();    A c = new C();}/*我们重点关注——用Java接口实现回调函数的等价功能简单来说，就是某个类的某个函数，接收一个接口作为参数（或者直接把该接口作为field）,那么就可以在这个函数中调用接口里面的方法了，称为回调而接口的实现可以千变万化，将不同的接口的实现类传入，就可实现不同的功能例如：*/interface Hello {    void sayHello();}class Man {        private Hello hello;        public Man(Hello hello) {        this.hello = hello;    }        public void say() {        hello.sayHello();    }    }class HelloTest {        public static void test() {        Man chinese = new Man(new Hello() {           public void sayHello() {               System.out.println("你好");           }        });        chinese.say();                Man english = new Man(new Hello() {            public void sayHello() {                System.out.println("hello");            }        });        english.say();    }}/* * 上面的例子是调用类“拥有接口”，接口是不知道调用类的 * 若接口和调用类要交互，那他们就是相互“拥有” * 考虑这样一个应用： NameChanger动态地改变Client的名字 * 那NameChanger的changeName方法就要接收一个Client对象，然后获取（调用）Client的名字并作不同的处理 * Client也要持有NameChanger，因为要打印改变后的名字 */class Client {    private INameChanger changer;    private String clientName;        public Client(INameChanger changer) {        this.changer = changer;    }    public void changeNameNow() {        String newName = changer.changeName(this);        this.clientName = newName;    }        public String getName() {        return clientName;    }    public void setName(String clientName) {        this.clientName = clientName;    }    }interface INameChanger {        String changeName(Client client);    }class ChangeNameTest {        public static void test() {                Client client = new Client(new INameChanger(){            public String changeName(Client client) {                return "Mr." + client.getName();            }        });        client.setName("Tom");        client.changeNameNow();        System.out.println(client.getName());                Client client2 = new Client(new INameChanger(){            public String changeName(Client client) {                return "Miss." + client.getName();            }        });        client2.setName("Lucy");        client2.changeNameNow();        System.out.println(client2.getName());            }    }/* * 考虑这样一个应用：希望在某个事件发生时得到通知 */interface InterestingEvent {        public void interestingEvent();    }class EventNotifier {        private InterestingEvent event;        //写成private List<InterestingEvent> eventList可以监听多个事件    private boolean somethingHappened;        public EventNotifier(InterestingEvent ie) {        this.event = ie;        this.somethingHappened = false;    }        public void setHappened() {        this.somethingHappened = true;    }        public void doWork() {        if (somethingHappened) {            event.interestingEvent();        }    }    }class ButtonPressedEvent implements InterestingEvent {    @SuppressWarnings("unused")    private EventNotifier en;        public ButtonPressedEvent() {        en = new EventNotifier(this);    }        public void interestingEvent() {        System.out.println("button pressed ");    }    }class EventNotifierTest {        public static void test() {        //这里有两种调用方法。其中第二种采用匿名内部类，其原理跟上面“改变Client名字”是一样的        EventNotifier en = new EventNotifier(new ButtonPressedEvent());        en.setHappened();        en.doWork();                EventNotifier en2 = new EventNotifier(new InterestingEvent(){            public void interestingEvent() {                System.out.println("inputtext change ");            }        });        en2.setHappened();        en2.doWork();            }}//这个类是用来测试的public class JavaInterfaceCallBack {        public static void main(String[] args) {        HelloTest.test();        ChangeNameTest.test();        EventNotifierTest.test();            }}