java-接口回调

/*
 * 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();
        
    }

}

评论

1 楼 tao_gun 2012-11-02