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CH10 – Mutable Objects

  1. If you haven’t completed Objects as Return Types, do so now.
  2. Open ObjectAsReturnType.java and add the following method.
public static void moveRect(Rectangle box, int dx, int dy){
  box.x = box.x + dx;
  box.y = box.y + dy;
}
  1. Add the following lines to the end of main.
moveRect(box,50,100);
System.out.println(box.toString());
  1. Compile and run the program.
$ javac ObjectAsReturnType.java 
$ java ObjectAsReturnType
java.awt.Rectangle[x=0,y=0,width=100,height=200]
java.awt.Point[x=50,y=100]
java.awt.Rectangle[x=50,y=100,width=100,height=200]

The complete class should appear as follows.

import java.awt.Rectangle;
import java.awt.Point;
public class ObjectAsReturnType{
  public static void main(String[] args){
    Rectangle box = new Rectangle(0,0,100,200);
    Point myPoint = ObjectAsReturnType.findCenter(box);
    System.out.println(box.toString());
    System.out.println(myPoint.toString());
    moveRect(box,50,100);
    System.out.println(box.toString());
  }
  public static Point findCenter(Rectangle box){
    int x = box.x + box.width / 2;
    int y = box.y + box.height / 2;
    Point retPoint = new Point(x,y);
    return retPoint;
  }
  public static void moveRect(Rectangle box, int dx, int dy){
    box.x = box.x + dx;
    box.y = box.y = dy;
  }
}