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Simplified Example Of How To Use JPanel & JFrame With Lots Of Different Stuff

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Below you will find a fully functional code example that shows how to do many common tasks with JPanel & JFrame. I stripped out as much useless "fluff" as I could, leaving the code as bare as possible( all code is in a single class ) .
If you have a question on a specific area please refer to a Google search before asking here.

Things this code demonstrates:
Buttons, and how to identify which one was clicked
Action listeners
Mouse listeners, and how to get exact click coordinates
Key listener
Focuses listener, and how to fix a common issue when using several listeners at one time
Drawing text and Unicode
Fonts, text size ,text styles, text colors
Popup windows
How to get anti-aliasing to actually work
Loading images from files and URLs
Resizing images
Drawing images

Please note: this code is not optimized - but it is a single class and fully functional !!!
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.event.*;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class Main extends JPanel implements KeyListener,ActionListener,MouseListener,FocusListener {

	  public static void main(String args[]) {
		  Main m = new Main(); // building object container - using " 'this' " will not work 
		  JFrame frame = new JFrame("Title Here"); // set title
		  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // set behavior when closed
		  frame.addKeyListener(m); // add keylistener
		  frame.addFocusListener(m); // add focuse listener
		  frame.addMouseListener(m); // add mouse listener
		  JButton button = new JButton("Click"); // build a button
		  button.setBounds(1, 200, 80, 30); // location and size of button
		  frame.add(button); // add a button
		  button.addActionListener(m); // something happens when button is clicked
		  frame.add(m); // package and create the Jframe
		  frame.setSize(new Dimension(300,300 )); // set window size
		  frame.setFocusable(true); // add focuse
		  button.setFocusable(true); // add focuse
		  frame.setVisible(true); // make the window  
  // This method is automatically called \\ 
  public void paintComponent(Graphics g) {
	Graphics2D g1 = (Graphics2D) g; // this is for antialiasing
	RenderingHints rh = new RenderingHints(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);// this is for antialiasing
    g1.setRenderingHints(rh);// this is for antialiasing
    g.setFont(new Font("Times New Roman",Font.BOLD,40)); // set font 
    try { // add an image ( replace "URL" with "File" if loading from local hard drive
    	Image img = ImageIO.read( new URL("http://img.brothersoft.com/icon/softimage/s/smileysidebar-387849-1280302029.jpeg") ); // get image from internet
		g.drawImage(img, 1, 100, null); // draw normal image
		g.drawImage(img.getScaledInstance(15, 15, Image.SCALE_DEFAULT), 1, 130, null); // draw resized image
	} catch (Exception e) {} // I'm too lazy to handle this error
    g.setColor(Color.black); // set text color
    g.drawString("Hello World ! ", 1, 30); // draw some words 
    g.drawString("\u263A", 1, 100); // draw some unicode

public void keyReleased(KeyEvent kr) { // do something when a key is released
	jo("You pushed a key ! \n Key Name: " + kr.getKeyChar() ); // create popup window when a key is pressed 
public void actionPerformed(ActionEvent bp) { // when a button is pressed, do something 
	jo("You pushed the button ! \n Button Name: " + bp.getActionCommand() ); // create popup window when button is pressed
}															// "getActionCommand()" is the name of button
public void mouseReleased(MouseEvent me) { // when a mouse button is clicked
	jo("Mouse clicked !\n Mouse Button: " + me.getButton() + "\nLocation Of Click: X-" +  me.getX() + " Y-" + me.getY() ); // were did you click ?
public void focusLost(FocusEvent fl) {
	fl.getComponent().requestFocusInWindow(); // this keeps the window focused
public void jo (String s){ // added this to save space else were
	JOptionPane.showMessageDialog( new JFrame(""), s); // popup wondow

// These methods have to be declared \\
public void keyTyped(KeyEvent kt) {}
public void keyPressed(KeyEvent kp) {}
public void focusGained(FocusEvent fg) {}
public void mouseClicked(MouseEvent me) {}
public void mouseEntered(MouseEvent me) {}
public void mouseExited(MouseEvent me) {}
public void mousePressed(MouseEvent me) {}


Jul 09 2014 08:32 PM

A screen shot of the above code may help more people understand how these components work.

Personally, I am not a huge fan of Java, but it is great for cross platform projects.

Jul 18 2014 02:40 AM

I personally no longer would spend Time with Java Swing. I was a Pro and used in Projects but, its simply out-of-date. You have to worry about stuff which should be provided by Swing. There are so many missing features. And the architecture is sometimes quite complicated so that you are not sure, if you misunderstood the MVC concept or if it is simply a problem of the API.

Jul 19 2014 12:32 PM

I see a couple of things that alone in that example might not be an issue but it could add up in a project.


Unnecesary objects:

There is no need for creating new RenderingHints each time the widget is drawn. You could just set them individually and since they're enums, no new object gets initialized.

Font object is getting created each time the thing is drawn, also it could be retained somewhere as a field.


Unnecesary work:

The Image is downloaded from internet (!) each time the widget is drawn, if you do that with several components, it will be slow as fuck. It should be loaded only once, maybe in the constructor, and stored as a field.


In any case, its a good example of the crazy things you can do when you start to implement all the listener interfaces :D

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