Question

I am making a sort of command based application to draw geometric figures. So if a user enters something like RECT 100, 50, 200, 120 I draw a rectangle at specified location on the drawing panel.

So for this i need to map RECT to g.drawRect(100, 50, 200, 120); and all such similar functions to draw geometric figures.

I will use a hash map for mapping, but i don’t know how to build a array of functions in java. In C++ i have done this though.

The key can be ‘RECT’ and the value the offset of the index.

Please show me how can i index these functions. Or is there a still better way to address the primary concern?

Answer 1

There are no function pointers in Java, you need to do it through inheritance and/or interfaces. Here is an example:

interface Shape {
    void draw(int[] data);
}

class Polygon implements Shape {
    public void draw(int[] data) {
        // Draw polygon using points data[i], data[i+1] for points
    }
}

class Circle implements Shape {
     public void draw(int[] data) {
         // Draw circle using data[0], data[1] for the center, and data[2] for radius
     }
}

In your main program’s constructor or static initializer:

Map<String,Shape> shapes = new HashMap<String,Shape>();
shapes.put("POLY", new Polygon());
shapes.put("CIRC", new Circle());

In your drawing code:

shapes.get("CIRC").draw(new int[] {100, 100, 50});