In this example we are going to create a simple application in which you can draw a simple shape (rectangle for example ) and drag it around our canvas. This is a very nice feature to use if your application has many graphical object 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
MouseListenerandMouseMotionListenerinterfaces. - Override
mouseClickedto handle mouse clicks,mouseEntered,mouseExitedmethods to check whether your mouse has entered or exited a certain area,mousePressedto monitor the mouse button clicks,mouseReleasedto check when the user releases a mouse button. - Override
mouseDraggedmethod in order to handle mouse drags. Userepaint()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.awt.Container;
import java.awt.Cursor;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class DrawSketch extends JPanel implements MouseMotionListener {
private static final int recW = 14;
private static final int MAX = 100;
private Rectangle[] rect = new Rectangle[MAX];
private int numOfRecs = 0;
private int currentSquareIndex = -1;
public DrawSketch() {
addMouseListener(new MouseAdapter() {
@Override
public void mousePressed(MouseEvent evt) {
int x = evt.getX();
int y = evt.getY();
currentSquareIndex = getRec(x, y);
if (currentSquareIndex < 0) // not inside a square
{
add(x, y);
}
}
@Override
public void mouseClicked(MouseEvent evt) {
int x = evt.getX();
int y = evt.getY();
if (evt.getClickCount() >= 2) {
remove(currentSquareIndex);
}
}
});
addMouseMotionListener(this);
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
for (int i = 0; i < numOfRecs; i++) {
((Graphics2D) g).draw(rect[i]);
}
}
public int getRec(int x, int y) {
for (int i = 0; i < numOfRecs; i++) {
if (rect[i].contains(x, y)) {
return i;
}
}
return -1;
}
public void add(int x, int y) {
if (numOfRecs < MAX) {
rect[numOfRecs] = new Rectangle(x, y, recW, recW);
currentSquareIndex = numOfRecs;
numOfRecs++;
repaint();
}
}
@Override
public void remove(int n) {
if (n < 0 || n >= numOfRecs) {
return;
}
numOfRecs--;
rect[n] = rect[numOfRecs];
if (currentSquareIndex == n) {
currentSquareIndex = -1;
}
repaint();
}
@Override
public void mouseMoved(MouseEvent event) {
int x = event.getX();
int y = event.getY();
if (getRec(x, y) >= 0) {
setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
} else {
setCursor(Cursor.getDefaultCursor());
}
}
@Override
public void mouseDragged(MouseEvent event) {
int x = event.getX();
int y = event.getY();
if (currentSquareIndex >= 0) {
Graphics graphics = getGraphics();
graphics.setXORMode(getBackground());
((Graphics2D) graphics).draw(rect[currentSquareIndex]);
rect[currentSquareIndex].x = x;
rect[currentSquareIndex].y = y;
((Graphics2D) graphics).draw(rect[currentSquareIndex]);
graphics.dispose();
}
}
public static void main(String[] args) {
JFrame jFrame = new JFrame();
jFrame.setTitle("");
jFrame.setSize(300, 200);
jFrame.addWindowListener(new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
Container cPane = jFrame.getContentPane();
cPane.add(new DrawSketch());
jFrame.setVisible(true);
}
}
This was an example on how to draw and drag a simple shape in a Java Desktop Application.
