学步园

<br /> /**<br /> * Callbacks.java<br /> * 通过内部类提供闭包的功能是优良的解决方案,它比指针更灵活,更安全.<br /> * --<Thingking in Java>第四版 Page 206<br /> */</p> <p>/** ********************************************************************* */<br /> interface Incrementable {<br /> void increment();<br /> }</p> <p>/** ********************************************************************* */<br /> // Very simple to just implement the interface:<br /> class Callee1 implements Incrementable {<br /> private int i = 0;</p> <p> public void increment() {<br /> i++;<br /> // System.out.println(i);<br /> System.out.println("[Callee1] --> " + i);<br /> }<br /> }</p> <p>/** ********************************************************************* */<br /> class MyIncrement {<br /> public void increment() {<br /> // System.out.println("Other operation");<br /> System.out.println("[MyIncrement] --> " + "Other operation");<br /> }</p> <p> static void f(MyIncrement mi) {<br /> mi.increment();<br /> }// 自己调用自己<br /> }</p> <p>/** ********************************************************************* */<br /> // If your class must implement increment() in<br /> // some other way, you must use an inner class:<br /> // 认真理解本类<br /> class Callee2 extends MyIncrement {//继承MyIncrement类<br /> private int i = 0;</p> <p> public void increment() {// 覆盖父类的方法<br /> super.increment();<br /> i++;<br /> // System.out.println(i);<br /> System.out.println("[Callee2] --> " + i);<br /> }</p> <p> // 内部类Closure提供了一个返回外围类Callee2的"钩子"(hook)-而且是一个安全的钩子<br /> private class Closure implements Incrementable {// 实现Incrementable接口<br /> public void increment() {<br /> // Specify outer-class method, otherwise<br /> // you'd get an infinite recursion:<br /> Callee2.this.increment();// 调用外围类的increment()方法<br /> }<br /> }</p> <p> Incrementable getCallbackReference() {<br /> return new Closure();<br /> }<br /> }</p> <p>/** ********************************************************************* */<br /> class Caller {// 回调类<br /> private Incrementable callbackReference;</p> <p> Caller(Incrementable cbh) {// 构造方法<br /> callbackReference = cbh;<br /> }</p> <p> void go() {<br /> callbackReference.increment();<br /> }<br /> }</p> <p>/** ********************************************************************* */<br /> public class Callbacks {<br /> public static void main(String[] args) {<br /> Callee1 c1 = new Callee1();<br /> Callee2 c2 = new Callee2();<br /> MyIncrement.f(c2); // 输出:Other operation<br /> /************************* 注意:这里应该输出的是,<br /> * ------------------<br /> * Other operation<br /> * 1<br /> * ------------------<br /> * 而不是"Other operation",原因是这样:调用Callee2(是MyIncrement的子类)的increment()方法<br /> */<br /> System.out.println("测试用--------");<br /> /*************使用回调类********************/<br /> Caller caller1 = new Caller(c1);<br /> Caller caller2 = new Caller(c2.getCallbackReference());//c2.getCallbackReference()返回一个Closure<内部类>的引用<><br /> caller1.go(); // 输出:1<br /> caller1.go(); // 输出:2<br /> caller2.go(); // 输出:Other operation<br /> // 输出:1<br /> /********************** 正确输出:2 *************/<br /> caller2.go(); // 输出:Other operation<br /> // 输出:2<br /> /********************** 正确输出:3 *************/<br /> }</p> <p>}<br /> /** ********************************************************************* */<br /> /* Output:<br /> Other operation<br /> 1<br /> 1<br /> 2<br /> Other operation<br /> 2<br /> Other operation<br /> 3<br /> *///:~<br />