What is the usage of Java callback functions?

In Java, a callback function is when one function is passed as an argument to another function, allowing the passed function to be called when certain events occur. Callback functions are typically used in asynchronous programming or event-driven programming.

In Java, callback functions are typically implemented using interfaces. For example, defining an interface Callback:

public interface Callback {
    void onCallback();
}

Then pass an implementation class of the Callback interface as a parameter in a certain method.

public void doSomethingAsync(Callback callback) {
    // 异步操作完成后调用回调函数
    callback.onCallback();
}

The process of using callback functions is as follows:

public class Main {
    public static void main(String[] args) {
        Callback callback = new Callback() {
            @Override
            public void onCallback() {
                System.out.println("Callback executed");
            }
        };

        doSomethingAsync(callback);
    }
}

In the example above, after the async operation is completed in the doSomethingAsync method, the provided callback function will be called to output “Callback executed”. This achieves the functionality of a callback function.

The use of callback functions can help decouple the program, making the code more flexible and scalable.