Develop Reference

Changing the sizes of a coloured square after pressing a button

I have written this code however I am having trouble with one aspect I wish to code into it. I want to make the green square change size when I press one of the three buttons I have so when I press the button 'small' the square changes size to small e.g. 100 and when I press the button 'medium' it changes size to medium e.g. 400. This is my code so far:
package Lab2;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Main {
public static void main(String[] args) {
FilledFrame frame = new FilledFrame();
frame.setVisible( true );
}
}
class FilledFrame extends JFrame {
int size = 400;
public FilledFrame()
{
JButton butSmall = new JButton("Small");
JButton butMedium = new JButton("Medium");
JButton butLarge = new JButton("Large");
JButton butMessage = new JButton("Say Hi");
SquarePanel panel = new SquarePanel(this);
JPanel butPanel = new JPanel();
butPanel.add(butSmall);
butPanel.add(butMedium);
butPanel.add(butLarge);
butPanel.add(butMessage);
add(butPanel, BorderLayout.NORTH);
add(panel, BorderLayout.CENTER);
setSize( size+100, size+100 ); } }
class SquarePanel extends JPanel {
FilledFrame theApp;
SquarePanel(FilledFrame app)
{
theApp = app;
}
public void paintComponent ( Graphics g)
{
super.paintComponent(g);
g.setColor(Color.green);
g.fillRect(20, 20, theApp.size, theApp.size);
}
}
class buttonHandler implements ActionListener {
FilledFrame theApp;
int size;
public buttonHandler(FilledFrame app, int size) {
theApp = app;
this.size = size;
}
#Override
public void actionPerformed (ActionEvent e){
theApp.setSize(this.size, this.size);
}
}

As I don't see any event listeners for your buttons, I assume this is all the code you have. Your buttons will not do anything unless you tell them to do it. You need to add event listeners, and through that change the size and update the panel.
Example:
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
theApp.size = 200;
frame.getContentPane().repaint();
//OR frame.repaint();
}
});
EDIT:
The problem with using the button handler class is you would need to find which buttton was pressed, instead its easier to use the way I showed above. I edited the code above, try copy pasting to one of the buttons.

Change JButton text and functionality depending on a specific situation

Basically what I am searching for is how to make a button's text and functionality change dynamically depending on the situation. For example I am working on a card game where I save selected cards of the user into an array, and I want it so when 1 or more card is selected, the button's name should be Play, and have the player to play that move, while if 0 cards are selected, the button's name should be Pass so on click the user can pass the turn. The button's text should change itself only depending on the number of selected cards, and not on click etc.
Image

The functionality part is easy, you just add action listener to the button as usual, but do something different depend on the number of selected cards.
As for the button text, you should have a method like updateButtonText() which assign different text to the button based on currently selected cards. And you call this method at start to assign the initial text.
Then whenever you detected user has change in card selection, you simply call updateButtonText() again to have the button text updated.

You could create two separate buttons where each has its own ActionListener and change which buttons are visible depending on the situation:
JButton pass_button = new JButton("Pass");
JButton play_button = new JButton("Play");
// Loop this code on separate thread or use callback
if(num_cards_selected == 0 && panel.contains(play_button)) {
panel.remove(play_button);
panel.add(pass_button);
} else if(num_cards_selected > 0 && panel.contains(pass_button)) {
panel.remove(pass_button);
panel.add(play_button);
}
Or you could check the state of the card game and have an ActionListener that is tied to the JButton act according to the condition:
JButton button = new JButton("");
// Loop this code on separate thread or use callback
if(num_cards_selected == 0)
button.setText("Pass");
else
button.setText("Play");
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(num_cards_selected == 0)
pass();
else
play();
}
});

What you need is :
check the number of cards selected
add action listener to button and change the outcome of the action as per the cards selection
Code example :
check all the comments provided in the code
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class cardGame implements ActionListener {
int cards[];
JButton b1;
JFrame f;
JPanel panel;
public cardGame(int n) { // taking input n as how many cards have been
// selected
cards = new int[n]; // number of cards selected
f = new JFrame(); // creating a jFrame
f.setPreferredSize(new Dimension(400, 400)); // size of JFrame
panel = new JPanel(); // creating a panel
b1 = new JButton("click"); // creating a JButton
b1.setSize(20, 30); // setting size of JButton
b1.addActionListener(this); // adding action listener
panel.add(b1); // adding JButton to panel
f.add(panel); // adding panel to JFrame
f.pack();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // setting default
// close operation
f.setVisible(true); // set JFrame visible
}
#Override
public void actionPerformed(ActionEvent e) {
if (cards.length >= 3) { // if cards are more than or equal to 3
// setBackground color blue
b1.setText("Play");
panel.setBackground(Color.blue);
}
// you can change the functionality as per your need
else {// else setBackground color green
b1.setVisible(true);
b1.setText("pass");
panel.setBackground(Color.green);
}
}
public static void main(String[] args) {
new cardGame(2); // providing input as number of cards selected try
// giving 2 and 3
}
}

Clear a JPanel from a JFrame

I'm working on an assignment for class where we need to create a JComboBox and each option opens a new window where you can do whatever you want on those new windows. Please keep in mind I'm very new to GUI and new to Java in general, in case my questions are dumb.
I have a question and an issue...
My question:
When the user selects "The Matrix" option a new window pops up with a quote and two buttons. Right now I have two JPanels (panel and panel2) panel adds the quote to the NORTH position and then panel2 adds the two buttons to the CENTER position both using BorderLayout. My question is am I doing this correctly...Could I use just panel to add the quote and the buttons or is it necessary to create separate panels for separate items being added to the JFrame? When I had them both added to the same panel the quote was not on the window when I ran the program.
panel.add(matrixQuote);
newFrame.add(panel, BorderLayout.NORTH);
That's how I had it when it wasn't showing up ^^^
I GOT THE ISSUE WITH CLEARING THE JFRAME FIXED
I am trying to add an ActionListener to the bluePill button and instead of opening another new window I thought I could clear everything from the existing window when the button is pressed and then display something new on said window. The only info I could find on this is how I have it in the actionPerformed method below. I'll post a snippet of what I'm talking about directly below and then all my code below that just in case.
All my code...
public class MultiForm extends JFrame{
private JComboBox menu;
private JButton bluePill;
private JButton redPill;
private JLabel matrixQuote;
private int matrixSelection;
private JFrame newFrame;
private JPanel panel;
private JPanel panel2;
private static String[] fileName = {"", "The Matrix", "Another Option"};
public MultiForm() {
super("Multi Form Program");
setLayout(new FlowLayout());
menu = new JComboBox(fileName);
add(menu);
TheHandler handler = new TheHandler();
menu.addItemListener(handler);
}
public void matrixPanel() {
TheHandler handler = new TheHandler();
//Create a new window when "The Matrix" is clicked in the JCB
newFrame = new JFrame();
panel = new JPanel();
panel2 = new JPanel();
newFrame.setLayout(new FlowLayout());
newFrame.setSize(500, 300);
newFrame.setDefaultCloseOperation(newFrame.EXIT_ON_CLOSE);
matrixQuote = new JLabel("<html>After this, there is no turning back. "
+ "<br>You take the blue pill—the story ends, you wake up "
+ "<br>in your bed and believe whatever you want to believe."
+ "<br>You take the red pill—you stay in Wonderland, and I show"
+ "<br>you how deep the rabbit hole goes. Remember: all I'm "
+ "<br>offering is the truth. Nothing more.</html>");
panel2.add(matrixQuote);
newFrame.add(panel2, BorderLayout.NORTH);
//Blue pill button and picture.
Icon bp = new ImageIcon(getClass().getResource("Blue Pill.png"));
bluePill = new JButton("Blue Pill", bp);
panel2.add(bluePill);
bluePill.addActionListener(handler);
//Red pill button and picture
Icon rp = new ImageIcon(getClass().getResource("Red Pill.png"));
redPill = new JButton("Red Pill", rp);
panel2.add(redPill);
newFrame.add(panel2, BorderLayout.CENTER);
newFrame.setVisible(true);
}
private class TheHandler implements ItemListener, ActionListener{
public void itemStateChanged(ItemEvent IE) {
//listen for an item to be selected.
if(IE.getStateChange() == ItemEvent.SELECTED) {
Object selection = menu.getSelectedItem();
if("The Matrix".equals(selection)) {
matrixPanel();
}
else if("Another Option".equals(selection)) {
}
}
}
public void actionPerformed(ActionEvent AE) {
if(AE.getSource() == bluePill) {
newFrame.remove(panel);
newFrame.remove(panel2);
newFrame.repaint();
}
}
}
//MAIN
public static void main(String[] args) {
MultiForm go = new MultiForm();
go.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
go.setSize(400, 200);
go.setVisible(true);
}
}

Use a Card Layout. You can swap panels as required.
The tutorial has a working example.

You can use:
jpanel.removeAll();
Either to delete a certain JComponent by using the JComponent itself like:
JFrame frame = new JFrame();
JPanel panel = new JPanel();
frame.add(panel);
frame.remove(panel);

panel.getGraphics().clearRect(0, 0, panel.getWidth(), panel.getHeight());

How to show/hide an image attached to a Jlabel after a Jbutton is clicked?

I'm new to programming world, and I need some help. I will try to be as clear as possible.
This is my current situation:
I'm programming a simple game.
On a Jframe, I've added a Jlabel on which I attached an image. I've also added a Jbutton on the Jframe.
I would like that when I click on the Jbutton, the image appears and on the next click the image hides.
How could I do it?
Thanks in advance and excuse me for the possible english mistakes.
EDIT
Following some instructions given by people, I've reached this point:
button.addActionListener(new Actionbox());
final class Actionbox implements ActionListener
{
public void actionPerformed (ActionEvent e)
{
if (label.getIcon() == null)
label.setIcon(new ImageIcon(myimage));
else
label.setIcon(null);
}
}
Eclipse is giving me an error message on the left side of the code editor, near the number lines. It says "Actionbox cannot be resolved to a type".
How could I solve it?

I would like that when I click on the Jbutton, the image appears and on the next click the image hides
add/remove an Icon from the label:
public void actionPerformed(ActionEvent e)
{
if (label.getIcon() == null)
label.setIcon(...);
else
label.setIcon( null );
}
Or instead of setting the Icon null, you may want to have a blank Icon so that the size of the label doesn't keep changing every time you show an image.

Don't fiddle with your button's visibility, and don't make it a final local variable. For something like this, the label should be a field. Place it in your GUI and leave it visible, since if it doesn't hold an icon or have text, nothing will show on it. Instead in your button's ActionListener, simply change the JLabel's ImageIcon via its setIcon(...) method. Pass in an Icon if you want to show an image and pass in null if you want to show nothing. Make your JLabel a field of the class, not a final local variable.
Regarding your code, one way to create your JButton's ActionListener is to use an anonymous inner class rather than a static private class. I'd also recommend reading in the image just once perhaps in your class's constructor and not each time the button is pressed. For example,
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;
#SuppressWarnings("serial") // have GUI extend JPanel
public class ButtonSwapImageGui extends JPanel {
private static final String IMAGE_PATH = "https://duke.kenai.com/iconSized/duke.gif";
private Icon imageIcon; // hold our image
private Icon nullImageIcon; // hold a blank image as a placeholder
private JLabel label = new JLabel("", SwingConstants.CENTER);
// throw an exception if image can't be read
public ButtonSwapImageGui() throws IOException {
// read in an image from the internet
URL imageUrl = new URL(IMAGE_PATH);
BufferedImage image = ImageIO.read(imageUrl);
// create a blank placeholder image the same size as
// the image read in from internet
int width = image.getWidth();
int height = image.getHeight();
BufferedImage nullImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
// create ImageIcon objects with images read in above
imageIcon = new ImageIcon(image);
nullImageIcon = new ImageIcon(nullImage);
// set JLabel with the placeholder nullImageIcon
label.setIcon(nullImageIcon);
// create our button
JButton button = new JButton("Swap Image");
// add an anonymous inner class ActionListener to button
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// get the JLabel's Icon
Icon currentIcon = label.getIcon();
// if the Icon matches the null icon
if (currentIcon == nullImageIcon) {
// set label with image
label.setIcon(imageIcon);
} else {
// otherwise the label is displaying the image
// so now set label with the null (blank) icon
label.setIcon(nullImageIcon);
}
}
});
// JPanel to hold our button
JPanel buttonPanel = new JPanel();
buttonPanel.add(button);
// set our GUI's layout to BorderLayout
setLayout(new BorderLayout());
// add the JLabel to the BorderLayout.CENTER position
add(label, BorderLayout.CENTER);
// add button JPanel to the bottom
add(buttonPanel, BorderLayout.PAGE_END);
}
private static void createAndShowGui() {
// declare our GUI JPanel
ButtonSwapImageGui mainPanel = null;
try {
mainPanel = new ButtonSwapImageGui();
} catch (IOException e) {
// if we're here, the image could not be read in
e.printStackTrace();
System.exit(-1); // can't get image -- exit program
}
JFrame frame = new JFrame("GUI");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel); // add GUI to JFrame
frame.pack(); // tell layout managers to layout components
frame.setLocationRelativeTo(null); // center GUI
frame.setVisible(true); // display GUI
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

You can do something like this:
button.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
jLabel.setVisible(!jLabel.isVisible()); //Note! jLabel has to be a final variable.
}
}
You should note that any variables used inside coming from outside the ActionListener have to be final ones. This largely restricts you into working with objects

I usually use set bounds (0,0,0,0); whenever I want to hide swing components
button.addActionListener(new Actionbox());
final class Actionbox implements ActionListener
{
public void actionPerformed (ActionEvent e)
{
if (label.getIcon() == null) {
label.setIcon(new ImageIcon(myimage));
else{
label.setIcon(null);
}
}

A main menu for class A extends Applet

Hi i have made a game in java that extends applet. The game works perfectly fine but one of the requirements of this assignment is that there should be a menu. For example: As the program is run a screen with "Play" and "Quit" Options should appear and if user clicks "Play", this should lead on to the game, etc...
Q) Is there a way to do this specifically for applets?
I have attempted to make a a menu using the following code but it doesn't work (I think this is only for extends JPanel or JFrame not extends Applet):
MainMenu.java
public class MainMenu extends JFrame {
int screenWidth = 200;
int screenHeight = 150;
int buttonWidth = 100;
int buttonHeight = 40;
JButton Play;
JButton Quit;
public MainMenu() {
addButtons();
addActions();
Play.setBounds((screenWidth - buttonWidth)/2, 5 , buttonWidth, buttonHeight); // Positions the play button
Quit.setBounds((screenWidth - buttonWidth)/2, 10 , buttonWidth, buttonHeight);
//Adding buttons
getContentPane().add(Play); //add the button to the Frame
getContentPane().add(Quit);
pack();
setVisible(true);
setLocationRelativeTo(null);
setSize(screenWidth , screenHeight);
setTitle("Drop");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setResizable(false);
}
private void addButtons() {
Play = new JButton ("Play");
Quit = new JButton ("Quit");
}
private void addActions() {
Play.addActionListener(new ActionListener() { // takes play button, adds new actionlistener
public void actionPerformed(ActionEvent e) { // Turn actionPerformed into variable for usage
dispose(); // wipes out Jframe
Board game = new Board();
game.run();
}
}); //Play Button
Quit.addActionListener(new ActionListener() { // takes quit button, adds new actionlistener
public void actionPerformed(ActionEvent e) { // Turn actionPerformed into variable for usage
System.exit(0);
}
}); //Quit Button
}
}
Launcher.java (Where menu is run from)
public class Launcher {
public static void main (String[] args){
new MainMenu();
}
}
Any help is much appreciated (Ideas, tutorials...)

For many components in one space, use a CardLayout as see in this short example.

I just ended up making a text based menu.
Initially set a variable to true, for eg: menu = true
and make the paint method paint whatever you want on the menu, like start...
if(menu) {
paint what's on the menu
}
then when when user clicks on a certain option within the menu turn menu variable to false i.e. menu = false.
You need to get mouse input to get the user's input so use either the mouse pressed or mouse clicked methods that come with the mouselistener.
After turning it false, get the paint method to paint your game.
i.e.
if(!menu) {
paint the game
}
Pretty much a bunch of if statements.
Hope this helps someone.