Computer Science 252
Problem Solving with Java

Spring 2015, The College of Saint Rose

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DragCars Demo

A working demo of DragCars will appear below. Click inside the applet to interact with it.

DragCars BlueJ Project

Click here to download a BlueJ project for DragCars.

DragCars Source Code

The Java source code for DragCars is below. Click on a file name to download it.

DragCars.java

import objectdraw.*;
import java.awt.*;

/*
 * Example DragCars: example using a car to demonstrate a custom class
 *
 * Jim Teresco, The College of Saint Rose, CSC 252, Spring 2014
 *
 * $Id: DragCars.java 2319 2014-02-07 01:24:52Z terescoj $
 */

public class DragCars extends WindowController {

    // background colors
    private static final Color SKY_BLUE = new Color(175, 175, 255);
    private static final Color NIGHT_SKY = new Color(10, 10, 100);
    
    // the three cars, and the sky backgrounds
    private Car car1, car2, car3;
    private FilledRect lightSky, darkSky;
    
    // dragging support -- draggingCar is null if no dragging, a 
    // reference to one of the cars if dragging
    private Location prevPoint;
    private Car draggingCar = null;
    
    public void begin() {
        
        // bright and dark portions
        lightSky = new FilledRect(0, 0, canvas.getWidth()/2, canvas.getHeight(), canvas);
        lightSky.setColor(SKY_BLUE);
        darkSky = new FilledRect(canvas.getWidth()/2, 0, canvas.getWidth()/2, canvas.getHeight(), canvas);
        darkSky.setColor(NIGHT_SKY);
    
        car1 = new Car(50, 50, Color.red, canvas);
        car2 = new Car(50, 250, Color.blue, canvas);
        car3 = new Car(200, 150, Color.green, canvas);
    }
    
    public void onMousePress(Location point) {
    
        if (car1.contains(point)) {
            draggingCar = car1;
        }
        else if (car2.contains(point)) {
            draggingCar = car2;
        }
        else if (car3.contains(point)) {
            draggingCar = car3;
        }
        
        prevPoint = point;
    }
    
    public void onMouseDrag(Location point) {
    
        if (draggingCar != null) {
            // standard dragging
            draggingCar.move(point.getX() - prevPoint.getX(),
                             point.getY() - prevPoint.getY());
            prevPoint = point;
            
            // check if we're supposed to turn the headlights on or off
            if (lightSky.contains(draggingCar.getCenter())) {
                draggingCar.turnOffHeadlights();
            }
            else {
                draggingCar.turnOnHeadlights();
            }
                
        }
    }
 
    public void onMouseRelease(Location point) {
        
        if (draggingCar != null) {
            // standard dragging
            draggingCar.move(point.getX() - prevPoint.getX(),
                             point.getY() - prevPoint.getY());
            prevPoint = point;
            
            // check if we're supposed to turn the headlights on or off
            if (lightSky.contains(draggingCar.getCenter())) {
                draggingCar.turnOffHeadlights();
            }
            else {
                draggingCar.turnOnHeadlights();
            }
                
        }
    
        draggingCar = null;
    }
     
    public void onMouseEnter(Location point) {
    
        car1.setColor(Color.red);
        car2.setColor(Color.blue);
        car3.setColor(Color.green);
    }
    
    public void onMouseExit(Location point) {
    
        if (car1.headlightsOn()) {
            car1.setColor(Color.gray);
        }
        if (car2.headlightsOn()) {
            car2.setColor(Color.gray);
        }
        if (car3.headlightsOn()) {
            car3.setColor(Color.gray);
        }
    }
}