Question

Is there a way in java to do something like this:

void fnc(void Reference_to_other_func());

What I’m trying is basically I have number of places where I need to display this same text to the user and the only difference is which method is invoked after this text. So for example instead of writing:

System.out.println("Hello");
f1();
//in some other place
System.out.println("Hello");
f2();
//etc

I would like to define one function:

public void f(void Reference_to_other_func())
{
System.out.println("Hello");
Reference_to_other_func();//HERE I'M INVOKING 
}

and then instead of repeating this whole code I could write something like this:

f(f1);
//in some other place
f(f2)
//etc.

Thanks for answers

Answer 1

Java does not have first-class functions, which makes most functional-programming techniques somewhat tedious to implement.

In this case, you can make an interface:

public interface Callback {
    void doCallback();
}

(Edit: or you could use java.util.concurrent.Callable<V>, which allows you to specify a return type)

then declare f to take an instance of this interface:

public void f(Callback callback) {
    System.out.println("Hello");
    callback.doCallback();
}

and pass an instance of this interface to the function:

f(new Callback() {
    public void doCallback() {
        f1();
    }
});
f(new Callback() {
    public void doCallback() {
        f2();
    }
});

As you can see, the gains are not going to become apparent unless you’re doing this quite a lot.