How To: Keeping component in bounds

Question

Hi,
I am working on creating a Container which allows components to be dragged around inside of it. This is similar to JDesktopPane which has JInternalFrames which can be moved around inside it...
Anyhow, I want to prevent a component from being dragged out of bounds. What I would like is the same affect as the JDesktopPane...where if a frame is dragged to the edge, it will just move around the edge, it wont go out...no what I mean? What I have implemented prevents the component from being dragged out of bounds, but when the component gets to the edge it just stops moving instead of sliding around the edge.
Any suggestions on what to do to improve this or make it like JDesktopPane (i have tried looking for the code in JDesktopPane and DefaultDesktopManager..but couldnt find it)..
here is what i currently do:
in the mouseDragged method i set the new location of the component according to the MouseEvent that occurred...
then i check to see if the 4 points (the top left, top right, bottom left, bottom right) of the component are contained within the container (i.e. myContainer.contains(top_leftPoint), etc)...
if all 4 points are in, then i do,
container.repaint()
else
component.setLocation(oldX, oldY)
container.repaint()
...any ideas?
Thanks...duke dollars are offered as well

Answer 1

Sorry again. Its not my best day today (influenza is coming up).
I don't know why I took JFrame as the container instead of the parent container.
Here is the improved version :
import java.awt.*;
import java.awt.Color;
import java.awt.Dimension;
import javax.swing.JPanel;
import javax.swing.border.LineBorder;
import javax.swing.border.TitledBorder;
public class Plate extends JPanel {
    private String name;
    private Container c;
    private Point top_leftPoint, top_rightPoint, bottom_leftPoint, bottom_rightPoint ;
    private Point top_leftPointC, top_rightPointC, bottom_leftPointC, bottom_rightPointC ;
    private int w,h,wC,hC;
    public Plate(String name) {
        this.name = name;
        init();
    private void init() {
        setPreferredSize(new Dimension(100, 100));
        setBorder(new TitledBorder(new LineBorder(Color.BLACK), name));
    private boolean isInContainer(){
        c = getParent();
        Rectangle r = new Rectangle( c.getWidth(), c.getHeight() );
        wC = (int)r.getWidth();
        hC = (int)r.getHeight();
        top_leftPointC = r.getLocation();
        top_rightPointC = new Point( (int)top_leftPointC.getX()+wC, (int)top_leftPointC.getY() );
        bottom_leftPointC = new Point( (int)top_leftPointC.getX(), (int)top_leftPointC.getY()+hC );
        bottom_rightPointC = new Point( (int)top_leftPointC.getX()+wC, (int)top_leftPointC.getY()+hC );
        w = getWidth();
        h = getHeight();
        top_leftPoint = getLocation();
        top_rightPoint = new Point( (int)top_leftPoint.getX()+w, (int)top_leftPoint.getY() );
        bottom_leftPoint = new Point( (int)top_leftPoint.getX(), (int)top_leftPoint.getY()+h );
        bottom_rightPoint = new Point( (int)top_leftPoint.getX()+w, (int)top_leftPoint.getY()+h );
        if( !r.contains(top_leftPoint) ) return false;
        if( !r.contains(top_rightPoint) ) return false;
        if( !r.contains(bottom_leftPoint) ) return false;
        if( !r.contains(bottom_rightPoint) ) return false;
        return true;
    public void stayInContainer(){
        /* if the plate goes is too far in right-direction, shift it back*/
        if( !isInContainer() ){   
            double x = top_rightPoint.getX();
            double xC = top_rightPointC.getX();
            if( x > xC ){
                setLocation( (int)(top_leftPoint.getX()+xC-x), (int)top_leftPoint.getY());
        /* if the plate goes is too far in left-direction, shift it back */
        if( !isInContainer() ){
            double x = top_leftPoint.getX();
            double xC = top_leftPointC.getX();
            if( x < xC ){
                setLocation( (int)(top_leftPoint.getX()+xC-x), (int)top_leftPoint.getY());
        /* if the plate goes is too far in top-direction, shift it back */
        if( !isInContainer() ){
            double y = top_leftPoint.getY();
            double yC = top_leftPointC.getY();
            if( y < yC ){
                setLocation( (int)top_leftPoint.getX(), (int)(top_leftPoint.getY()+yC-y));
        /* if the plate goes is too far in bottom-direction, shift it back */
        if( !isInContainer() ){
            double y = bottom_leftPoint.getY();
            double yC = bottom_leftPointC.getY();
            if( y > yC ){
                setLocation( (int)top_leftPoint.getX(), (int)( top_leftPoint.getY()+yC-y) );
import java.awt.*;
import java.awt.Component;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.JPanel;
public class PlateCanvas extends JPanel implements MouseListener, MouseMotionListener {
    private Plate hitPlate;
    private double deltaX;
    private double deltaY;
    Point previousLocation;
    boolean first = true;
    public PlateCanvas() {
        init();
    private void init() {
        addMouseListener(this);
        addMouseMotionListener(this);
    public void mouseClicked(MouseEvent e) {
    public void mouseEntered(MouseEvent e) {
    public void mouseExited(MouseEvent e) {
    public void mousePressed(MouseEvent e) {
        Component c = getComponentAt(e.getPoint());
        if (c instanceof Plate) {
            hitPlate = (Plate) c;
            deltaX = e.getX() - hitPlate.getX();
            deltaY = e.getY() - hitPlate.getY();
    public void mouseReleased(MouseEvent e) {
        hitPlate = null;
    int max,newX,newY;
    public void mouseDragged(MouseEvent e) {
        if (hitPlate != null) {
            int x = (int) (e.getX() - deltaX);
            int y =     (int) (e.getY() - deltaY);
            hitPlate.setLocation(x, y);
            hitPlate.stayInContainer();
            repaint();
    public void mouseMoved(MouseEvent e) {
import javax.swing.JFrame;
public class TestPlates {
    public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        PlateCanvas mainPanel = new PlateCanvas();
        Plate p1 = new Plate("Plate 1");
        Plate p2 = new Plate("Plate 2");
        Plate p3 = new Plate("Plate 3");
        mainPanel.add(p1);
        mainPanel.add(p2);
        mainPanel.add(p3);
        f.getContentPane().add(mainPanel);
        f.setSize(800, 600);
        f.setVisible(true);
}