Computer Science 252
Problem Solving with Java

Spring 2014, The College of Saint Rose

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FallingBallSlider Demo

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

FallingBallSlider BlueJ Project

Click here to download a BlueJ project for FallingBallSlider.

FallingBallSlider Source Code

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

FallingBallSlider.java

import objectdraw.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JSlider;
import javax.swing.JPanel;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

/*
 * Example FallingBallSlider: a slider for finer control over
 * ball speeds.
 *
 * Jim Teresco, The College of Saint Rose, CSC 252, Fall 2013
 *
 * $Id: FallingBallSlider.java 2227 2013-10-24 03:37:54Z terescoj $
 */

// Note here that our class serves as both an ActionListener and
// a ChangeListener, so we specify that it implements both, and
// separate by commas. A class can implement as many interfaces
// as we wish, so long as we provide all of the required methods
// for each interface.
public class FallingBallSlider extends WindowController 
    implements ActionListener, ChangeListener {

    private static final int MIN_SPEED = 2;
    private static final int MAX_SPEED = 10;

    // using a JSlider this time
    private JSlider speedControl;
    
    // the ball, so we can set its speed
    private Ball lastLaunch;
    
    public void begin() {
        setSize(500, 500);

        // We still need our content pane
        Container contentPane = getContentPane();

        // A JPanel, in which we will group together our JButton
        // and JComboBox
        JPanel northPanel = new JPanel();

        // Next, we'll create just one button and add it to our
        // JPanel.
        JButton createBallButton = new JButton("Drop Ball");
        northPanel.add(createBallButton);

        // construct a JSlider:
        // the first parameter is orientation, we choose horizontal
        // the remaining parameters are the values associated with
        // the minimum, maximum, and initial values of the slider
        speedControl = new JSlider(JSlider.HORIZONTAL, MIN_SPEED, MAX_SPEED, MIN_SPEED);
        
        // and put our JSlider into our JPanel
        northPanel.add(speedControl);

        // now, we add the JPanel (which contains our JButton
        // and JPanel) to the content pane, this time in the
        // north, why not?
        contentPane.add(northPanel, BorderLayout.NORTH);

        // add our action listener for the button
        createBallButton.addActionListener(this);
        // and our change listener for the slider
        speedControl.addChangeListener(this);

        // put at end of all methods that change the layout
        contentPane.validate();
    }

    // actionPerformed this time only deals with creating a new
    // ball, but it needs to query the current slider state
    // to decide on the ball's initial speed.
    public void actionPerformed(ActionEvent e) {
        
        // get the speed from the JSlider
        double speed = speedControl.getValue();
        
        // go ahead and create the new ball
        lastLaunch = new Ball(new Location(200, 0), speed, canvas);
    
    }
    
    // our slider generates ChangeEvents, delivered to
    // the stateChanged method, as required by the ChangeListener
    // interface
    public void stateChanged(ChangeEvent e) {

        // if we've launched a ball, set its speed.
        if (lastLaunch != null) {
            lastLaunch.setSpeed(speedControl.getValue());
        }
    }
    
}