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//: innerclasses/Callbacks.java

// Using inner classes for callbacks

package innerclasses;

import static net.mindview.util.Print.*;

interface Incrementable {

void increment();

}

// Very simple to just implement the interface:

class Callee1 implements Incrementable {

private int i = 0;

public void increment() {

i++;

print(i);

}

}

class MyIncrement {

public void increment() { print("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 {

private int i = 0;

public void increment() {

super.increment();

i++;

print(i);

}

private class Closure implements Incrementable {

public void increment() {

// Specify outer-class method, otherwise

// you'd get an infinite recursion:

Callee2.this.increment();

}

}

Incrementable getCallbackReference() {

return new Closure();

}

}

class Caller {

private Incrementable callbackReference;

Caller(Incrementable cbh) { callbackReference = cbh; }

void go() { callbackReference.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();

}

} /* Output:

Other operation

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Other operation

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Other operation

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*///:~