=========== Point.java =============================== class Point { private int x; private int y; public int getX() { return x;} public int getY() { return y;} public int sum() { return x+y;} protected void setX (int xval) { x = xval;} protected void setY (int yval) { y = yval;} protected void move (int dx, int dy) { x = x + dx; y = y + dy;} Point(int xval, int yval) { x = xval; y = yval;} } =========== CPoint.java =============================== class CPoint extends Point { private int c; public int getC() { return c;} public int sum() { return super.sum() + c ;} protected void setC (int cval) { c = cval;} CPoint(int xval, int yval, int cval) { super(xval,yval); c=cval; } } =========== Test.java =============================== import java.io.*; class Test { public static void main(String args[]){ Point p; CPoint q; q = new CPoint(10,20,3); System.out.println(q.sum()); p = q; System.out.println(p.sum()); // System.out.println(p.getC()); // error // q = p; // error } }