Java编程思想中关于闭包的一个例子

Java编程思想中的一个例子，不是很理解使用闭包的必要性，如果不使用闭包，是不是有些任务就不能完成？继续探索。

package InnerClass;

interface Incrementable {
    void increment();
}

/** 被调1 */
// Very simple to just implement the interface
class Callee1 implements Incrementable {
    private int i = 0;

    @Override
    public void increment() {
        i++;
        System.out.println("Callee1" + i);
    }
}

class MyIncrement {
    public void increment() {
        System.out.println("other operation");
    }

    static void f(MyIncrement mi) {
        mi.increment();
    }
}

// if your class must implement increment() in some other way, you must use an
// inner class
class Callee2 extends MyIncrement implements Incrementable {
    private int i = 0;

    public void increment() {
        super.increment();
        i++;
        System.out.println("Callee2：" + i);
    }

    private class Closure implements Incrementable {
        public void increment() {
            System.out.println("内部类实现接口");//1.这句是我加的。
            Callee2.this.increment();//2.既然想表达与外部类的不同，此处为何还要调用外部类的方法实现同一个功能，造成迷惑
        }
    }

    Incrementable getCallbackReference() {
        return new Closure();
    }
}

class Caller {
    private Incrementable callbarckReference;

    public Caller(Incrementable chb) {
        callbarckReference = chb;
    }

    void go() {
        callbarckReference.increment();
    }
}

public class Callbacks {

    public static void main(String[] args) {
        Callee1 c1 = new Callee1();
        Callee2 c2 = new Callee2();

        MyIncrement.f(c2);
        Caller caller1 = new Caller(c1);
        Caller caller2 = new Caller(c2.getCallbackReference());
        caller1.go();
        caller1.go();
        caller2.go();
        caller2.go();
    }
}