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About Byron Kiourtzoglou

Byron Kiourtzoglou
Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Drag event example

With this example we shall show you how to work with MouseListener and MouseMotionListener interfaces in order to handle and monitor mouse events an especially mouse drags. This is a very nice feature to use if your application has many graphical objects that the user needs to move around the screen very frequently. It’s is very user friendly to let the user drag the object to perform these kinds of actions.

Basically all you have to do in order to handle mouse drags and mouse moves is:

  • Create a class that implements MouseListener and MouseMotionListener interfaces.
  • Override mouseClicked to handle mouse clicks, mouseEnteredmouseExited methods to check whether your mouse has entered or exited a certain area, mousePressed to monitor the mouse button clicks, mouseReleased to check when the user releases a mouse button.
  • Override mouseDragged method in order to handle mouse drags. Use repaint() method to repaint the object in its new position.

Let’s take a look at the code snippets that follow:

package com.javacodegeeks.snippets.desktop;

import java.applet.Applet;
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Label;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JApplet;
//Double buffering to make it repaint faster.

public class DragRect extends JApplet {

    static protected Label lab = new Label(

"Drag the rectangle with your mouse");

    @Override
    public void init() {

  getContentPane().setLayout(new BorderLayout());

  getContentPane().add(new MyCanvas());

  getContentPane().add("South", lab);
    }

    public static void main(String s[]) {

  Frame frame = new Frame("ShapeMover");

  frame.addWindowListener(new WindowAdapter() {

@Override

public void windowClosing(WindowEvent e) {

    System.exit(0);

}

  });

  Applet app = new DragRect();

  frame.add("Center", app);

  app.init();

  frame.pack();

  frame.setSize(new Dimension(550, 250));

  frame.setVisible(true);
    }
}
class MyCanvas extends Canvas implements MouseListener, MouseMotionListener {

    Rectangle rectangle = new Rectangle(0, 0, 70, 60);
    Graphics2D graphic2D;
    int pX, pY;
    boolean ftime = true;
    Rectangle shape;
    boolean pOut = false;

    public MyCanvas() {

  setBackground(Color.BLUE);

  addMouseMotionListener(this);

  addMouseListener(this);
    }

    @Override
    public void mousePressed(MouseEvent event) {

  pX = rectangle.x - event.getX();

  pY = rectangle.y - event.getY();

  if (rectangle.contains(event.getX(), event.getY())) {

updateLocation(event);

  } else {

DragRect.lab.setText("Drag the shape with your mouse.");

pOut = true;

  }
    }

    @Override
    public void mouseDragged(MouseEvent event) {

  if (!pOut) {

updateLocation(event);

  } else {

DragRect.lab.setText("Drag the shape with your mouse.");

  }
    }

    @Override
    public void mouseReleased(MouseEvent event) {

  if (rectangle.contains(event.getX(), event.getY())) {

updateLocation(event);

  } else {

DragRect.lab.setText("Drag the shape with your mouse.");

pOut = false;

  }
    }

    @Override
    public void mouseMoved(MouseEvent e) {
    }

    @Override
    public void mouseClicked(MouseEvent e) {
    }

    @Override
    public void mouseExited(MouseEvent e) {
    }

    @Override
    public void mouseEntered(MouseEvent e) {
    }

    public void updateLocation(MouseEvent e) {

  rectangle.setLocation(pX + e.getX(), pY + e.getY());

  if (checkRect()) {

DragRect.lab.setText(rectangle.getX() + ", " + rectangle.getY());

  } else {

DragRect.lab.setText("Drag the shape with your mouse.");

  }

  repaint();
    }

    @Override
    public void paint(Graphics g) {

  update(g);
    }

    @Override
    public void update(Graphics g) {

  Graphics2D g2 = (Graphics2D) g;

  Dimension dim = getSize();

  int w = (int) dim.getWidth();

  int h = (int) dim.getHeight();

  g2.setStroke(new BasicStroke(8.0f));

  if (ftime) {

shape = new Rectangle(dim);

rectangle.setLocation(w / 2 - 50, h / 2 - 25);

ftime = false;

  }

  g2.setPaint(Color.white);

  g2.fillRect(0, 0, w, h);

  g2.setColor(Color.red);

  g2.draw(rectangle);

  g2.setColor(Color.black);

  g2.fill(rectangle);
    }

    boolean checkRect() {

  if (shape == null) {

return false;

  }

  if (shape.contains(rectangle.x, rectangle.y, 100, 50)) {

return true;

  }

  int new_x = rectangle.x;

  int new_y = rectangle.y;

  if ((rectangle.x + 100) > shape.getWidth()) {

new_x = (int) shape.getWidth() - 99;

  }

  if (rectangle.x < 0) {

new_x = -1;

  }

  if ((rectangle.y + 50) > shape.getHeight()) {

new_y = (int) shape.getHeight() - 49;

  }

  if (rectangle.y < 0) {

new_y = -1;

  }

  rectangle.setLocation(new_x, new_y);

  return false;
    }
}

 
This was an example on how to handle object dragging in Java.

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