Question

I’m trying to make a list of function calls. I want to be able to call a specific method by simply choosing the method from an array.

So for example if I want to call, drawCircle() and that method is in the first index than I could say runMethod[0].

Here’s what I have so far. I’ve made an interface with two inputs:

public interface Instruction {  
   void instr( int a, int b );
} 

In my other class I have a list of methods (or should they be classes that implement Instruction?). I want to be able to call any of these methods from a list, like so:

instList[0].mov( 1, 3 );
instList[2].add( 4, 5 );

and so on. Hope that was clear enough. Thanks in advance.

Answer 1

If by “make method calls dynamically” you mean making method calls against an interface and let Java choose which code is executed: This is simply polymorphism via dynamic dispatch, so provide different implementations:

class Mov implements Instruction {
    void instr(int a, int b) {
        // code for moving here
    }
}

class Add implements Instruction {
    void instr(int a, int b) {
        // code for adding here
    }
}

You can then use instances of these implementations, e.g. in an array. Dynamic dispatch will choose the right code for each instance when calling instr. But I wonder if such a general interface and an array of implementing instances is a good design. If I could, I’d use more specific interfaces and hold instances in separate variables. Your approach does make sense if you want to implement the Command pattern, i.e. you

• have different clients that should be able to handle different sets of commands, or
• want to queue or log or undo/redo all the commands.

If by “make method calls dynamically” you mean duck typing, this is only in a difficult way possible, see this conference paper on the International Conference on Software Engineering 2011.