CallBack methods

[Em Aiy]

hi

there have been options that we don in c/c++ that we can make callback function ... i.e on a particular event the function calls automatically (provided the name of the pointer to the function).

how can we do this in java.

[Peter Chase]

In C, call-backs are done by passing function pointers, as you suggest. In C++, the C approach works, but is not recommended, as it is not object-oriented.

In C++ and Java, it is better to define a call-back interface and then to pass an object implementing that call-back interface. That's the more object-oriented way.

[Em Aiy]

thanks peter, but can you explain it in a bit detail.

well, one more thing confusing is taht, in c we tell exactly which function is to call by telling its pointer, but the way you are telling is telling the object. now we have to explicitly call the specified function from that class, isn't it so?

i have seen a call back method type api in winPCap api, which is used to analyze the network trafic. how may they have implemented things?

[Peter Chase]

See this thread.

[Jesper de Jong]

Here's a simple example with an interface, and an anonymous inner class in the main() method that implements the interface.

public class Main {
    public static void doSomething(String[] names, Callback cb) {
        for (String name : names) {
            // Call the callback method with the current name
            cb.callbackMethod(name);
        }
    }
 
    public static void main(String args[]) {
        String[] names = { "Tom", "Jerry", "Brigitte" };
 
        doSomething(names, new Callback() {
            public void callbackMethod(String name) {
                System.out.println("Hello " + name + "!");
            }
        });
    }
}
 
interface Callback {
    void callbackMethod(String name);
}