java wildcards examples

Specifying upper bound with extends

    // drawAll() can draw a list of shapes as well as a list of subtype of
    // shapes
    public static void drawAll(Collection<? extends Shape> shapes) {
        for (Shape s : shapes) {
            s.draw();
        }
    }

    public static void main(String[] args) {

        // create a list of triangles
        List<Triangle> triangles = new ArrayList<Triangle>();

        // add triangle1 to triangle list
        Triangle t1 = new Triangle();
        triangles.add(t1);

        // add triangle2 to triangle list
        Triangle t2 = new Triangle();
        triangles.add(t2);

        // call drawAll() to draw a list of triangles
        drawAll(triangles);
    }

Specifying lower bound with super

    // finding the max value
    // T implements Comparator of super type of T
    public static <T extends Comparator<? super T> > T max( T[] arr ) {

        if (arr == null || arr.length == 0)
            throw new IllegalArgumentException();

        T m = arr[0];

        int len = arr.length;
        for (int i = 1; i < len; i++) {
            if ( m.compare(m, arr[i]) < 0 )
                m = arr[i];
        }

        return m;
    }