Reference to fnc

Is there a way in java to do开发者_如何学Go 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

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.

By Reflection you could get the actual Method object and then do.

public void f(Method m) { System.out.println("Hello"); m.invoke(this, null); }

Unfortunately (IMHO) methods (functions) are not first-class objects in java, meaning that you can't create anonymous or named methods, without attaching it to a class first.

You could implement a class that only do one thing (for instance, like Callable or Runnable does)

You can create a anonymous class like this:

    Runnable x = new Runnable(){

        @Override
        public void run() {
            // TODO Auto-generated method stub

        }

    };   //<-- notice the semi-colon.

and you can define your function f like this:

public void f( Runnable x ) {
   System.out.println("Hello");
   x.run();
}

}

And call it like this.

...
// call the f-function :-)
f( new Runnable(){
@Override
public void run() {
    System.out.println("World!");
    }   
}});