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Trying to display images in multiple JPanels

I'm creating a program that features a grid of 12 JPanels. When the "add image" button is pressed, an image appears in the first JPanel in the grid and a counter is incremented by one. From then onwards, every time the "add image" is clicked again, an image would be added to the next JPanel. For some reason, the button only adds an image to the first JPanel and then stops working. Here's the code I've got so far.
public class ImageGrid extends JFrame {
static JPanel[] imageSpaces = new JPanel[12];
int imageCounter = 0;
ImageGrid() {
this.setTitle("Image Grid");
setSize(750, 750);
setDefaultCloseOperation(EXIT_ON_CLOSE);
JPanel p3 = new JPanel();
p3.setLayout(new GridLayout(3, 4, 10, 5));
p3.setBackground(Color.WHITE);
p3.setOpaque(true);
p3.setBorder(BorderFactory.createEmptyBorder(0, 5, 5, 5));
for (int j = 0; j < imageSpaces.length; j++) {
imageSpaces[j] = setImageSpace();
p3.add(imageSpaces[j]);
}
MyButtonPanel p1 = new MyButtonPanel();
add(p1, BorderLayout.SOUTH);
add(p3, BorderLayout.CENTER);
}
public JPanel setImageSpace() {
JPanel test;
test = new JPanel();
test.setOpaque(true);
test.setPreferredSize(new Dimension(100, 100));
return test;
}
class MyButtonPanel extends JPanel implements ActionListener {
final JButton addImage = new JButton("Add Image");
ImageIcon lorryPicture = new ImageIcon(ImageGrid.class.getResource("/resources/lorry.png"));
JLabel lorryImage = new JLabel(lorryPicture);
MyButtonPanel() {
add(addImage);
addImage.addActionListener(this);
}
public void actionPerformed(ActionEvent e) {
if (e.getSource() == addImage) {
imageSpaces[imageCounter].add(lorryImage);
revalidate();
repaint();
imageCounter++;
}
}
}
public static void main(String[] args) {
ImageGrid test = new ImageGrid();
test.setVisible(true);
}
}

You should be revalidating and repainting the panel, (which is the containter being affected by the addition), not the frame
imageSpaces[imageCounter].add(lorryImage);
imageSpaces[imageCounter].revalidate();
imageSpaces[imageCounter].repaint();
Diclaimer: This may work as a simple fix, but also note that a component (in this case your JLabel lorryImage) can only have one parent container. The reason the above fix still works is because you don't revalidate and repaint the previous panel, the label was added to. So you may want to think about doing it correctly, and adding a new JLabel to each panel.
if (e.getSource() == addImage) {
JLabel lorryImage = new JLabel(lorryPicture);
imageSpaces[imageCounter].add(lorryImage);
imageSpaces[imageCounter].revalidate();
imageSpaces[imageCounter].repaint();
imageCounter++;
}
Disclaimer 2: You should add a check, to only add a label if the count is less than the array length, as to avoid the ArrayIndexOutOfBoundsException
Side Notes
Swing apps should be run from the Event Dispatch Thread (EDT). You can do this by wrapping the code in the main in a SwingUtilities.invokeLater(...). See more at Initial Threads
You could also just use a JLabel and call setIcon, instead of using a JPanel

Resize JButtons in a BoxLayout

I'm trying to make a simple menu for my game. I have 4 buttons in the center and I want to make them a little bit bigger and center them.
The last part worked but I can't seem to call any of my JButtons and do a .setSize / .setPreferedSize(new Dimension()) on it.
public class mainMenu extends JFrame {
private JButton start, highscore, help, stoppen;
public mainMenu() {
super("Master Mind");
maakComponenten();
maakLayout();
toonFrame();
}
private void maakComponenten() {
start = new JButton("Start");
start.setBackground(Color.gray);
highscore = new JButton("Higscores");
help = new JButton("Help");
stoppen = new JButton("Stoppen");
}
private void maakLayout() {
JPanel hoofdmenu = new JPanel();
hoofdmenu.setLayout(new BoxLayout(hoofdmenu, BoxLayout.Y_AXIS ));
hoofdmenu.add(start);
start.setAlignmentX(CENTER_ALIGNMENT);
hoofdmenu.add(highscore);
highscore.setAlignmentX(CENTER_ALIGNMENT);
hoofdmenu.add(help);
help.setAlignmentX(CENTER_ALIGNMENT);
hoofdmenu.add(stoppen);
stoppen.setAlignmentX(CENTER_ALIGNMENT);
super.add(hoofdmenu);
}
private void toonFrame() {
setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
setVisible(true);
setSize(500,500);
}
public static void main(String[] args) {
new mainMenu();
}
}

As an example, to change the size of the "Start" button,
change :
start1 = new JButton("Start");
to
start1 = new JButton("Start") {
{
setSize(150, 75);
setMaximumSize(getSize());
}
};

The problem is that JFrames use BorderLayout by default, which means that your JPanel will naturally fill the space.
Before adding your JPanel, call the following code to change the JFrame's layout to null and use the JPanel's settings instead.
this.setLayout(null);
JPanel hoofdmenu = new JPanel();
hoofdmenu.setBounds(0,0, 400, 100);
Alternatively, you could set the maximum size of the JButtons
Dimension maxSize = new Dimension(100, 100);
start.setMaximumSize(maxSize);
highscore.setMaximumSize(maxSize);
help.setMaximumSize(maxSize);
stoppen.setMaximumSize(maxSize);

Here's another example following behind the previous two - I'm making a soundboard program, and this is actually a sample from it - The JPanel actually is needed, agreeing to the second post.
JFrame frame = new JFrame();
JPanel menuPanel = new JPanel();
JButton Button1 = new JButton("<BUTTON NAME 1>");
Button1.setSize(80, 30);
Button1.setLocation(4, 4);
JButton Button2 = new JButton("<BUTTON NAME 2>");
Button2.setSize(80, 30);
Button2.setLocation(90, 4);
Ah, and another thing - You created the buttons in a different block from the second piece of code. Doing that causes the other blocks to not see it. You need to declare them outside the block so all the blocks can see them.

Java GUI NullPointerException with Canvas class

So I am working on a GUI project for my class and I am a bit stuck. My problem has to do with my GUI aspect so I guess you could ignore the other methods having to do with the sorting. As of now, my main concern is just getting the GUI working. However, I keep running into an error, a null pointer exception to be exact:
Java.lang.NullPointerException
at SortDriver$SortCanvas.paint(SortDriver.java:253)
at SortDriver.init(SortDriver.java:197)
at sun.applet.AppletPanel.run(AppletPanel.java:436)
at java.lang.Thread.run(Thread.java:679)
After reading though my code, I think I narrowed it down to the my SortCanvas class. I never used it before but it was part of the stub my professor gave to us. That is to say that it works correctly and displays the image correctly but it looks like my implementation is incorrect however. Could someone help me figure out how to implement my SortCanvas "picture" correctly please? I read over the Java Docs for Canvas and I still don't understand what I am doing wrong. Here is my code:
import java.awt.*;
import java.applet.Applet;
import javax.swing.*;
import java.awt.event.*;
public class SortDriver extends Applet {
private int array[]; // array to be sorted
private int limit = 1000; // size of array to be sorted - you may have to make
// this bigger for faster sorts
private int largestNum; // need to know for color scaling purposes in paint()
// flag to tell paint() whether to paint a single location or the whole array
private enum PaintType {ALL, SINGLE};
private PaintType doPaint = PaintType.ALL;
private int index = -1; // index of single array location to be painted
//this listener object responds to button events
private ButtonActionListener buttonListener;
//button to start the sort
private JButton sortButton;
//basic window frame
private JFrame mainFrame;
//layouts
private BorderLayout initialLayout;
private FlowLayout northLayout;
private BorderLayout centerLayout;
private BorderLayout southLayout;
//basic panel for window frame
private JPanel initialPanel;
//panels for window layout
private JPanel northPanel;
private JPanel centerPanel;
private JPanel southPanel;
//panels for radio buttons
private JPanel radioOrderPanel;
private JPanel radioSortPanel;
private JPanel radioColorPanel;
//north panel header labels
private JLabel topTitleLabel;
private JLabel bottomTitleLabel;
private JLabel arraySizeLabel;
//radio buttons for list order (radioOrderButton)
//random set, ordered set, reverse set
private JRadioButton rOB1, rOB2, rOB3;
//radio buttons for sort type (radioSortButton)
//bubblesort, insertionsort, mergesort, quicksort
private JRadioButton rSB1, rSB2, rSB3, rSB4;
//radio buttons for color choice (radioColorButton)
//green, red, white, blue
private JRadioButton rCB1, rCB2, rCB3, rCB4;
//radio button groups for each radio panel
private ButtonGroup orderGroup, sortGroup, colorGroup;
//text field for size of the array
private JTextField arraySizeTextField;
// the picture of the sort will appear on this canvas
private SortCanvas picture;
private final int pictureWidth = 500; // size of the sort bar 1001
private final int pictureHeight = 50;
public void init() {
buttonListener = new ButtonActionListener();
array = new int[limit];
// load the array
largestNum = array[0] = (int) (Math.random()*1000000.0);
for (int i=1; i<limit; i++) {
array[i] = (int) (Math.random()*1000000.0);
// also keep track of the largest so that we can scale by it in paint()
if (array[i] > largestNum) largestNum = array[i];
}
//set up the main frame
mainFrame = new JFrame();
initialPanel = (JPanel) mainFrame.getContentPane();
initialLayout = new BorderLayout();
mainFrame.setResizable(false);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
mainFrame.setSize(650, 750);
initialPanel.setLayout(initialLayout);
//set up north panel
northPanel = new JPanel();
northLayout = new FlowLayout();
topTitleLabel = new JLabel("SortIt!");
bottomTitleLabel = new JLabel("A program by Mike Sevilla");
northPanel.setLayout(northLayout);
northPanel.add(topTitleLabel, BorderLayout.NORTH);
northPanel.add(bottomTitleLabel, BorderLayout.NORTH);
initialPanel.add(northPanel, BorderLayout.NORTH);
//set up center panel
centerPanel = new JPanel();
centerLayout = new BorderLayout();
centerPanel.setLayout(centerLayout);
//place array size label
arraySizeLabel = new JLabel("Size:");
//place array size text field w/ space for 5 chars
arraySizeTextField = new JTextField("", 5);
//place sort button
sortButton = new JButton("Sort it!");
// the listener is triggered when the button is clicked
sortButton.addActionListener(buttonListener);
centerPanel.setLayout(centerLayout);
//place sort bar on top of center layout
picture = new SortCanvas();
centerPanel.add(picture, BorderLayout.CENTER);
centerPanel.add(arraySizeLabel, BorderLayout.CENTER);
centerPanel.add(arraySizeTextField, BorderLayout.CENTER);
centerPanel.add(sortButton, BorderLayout.CENTER);
initialPanel.add(centerPanel, BorderLayout.CENTER);
//set up south panel
southPanel = new JPanel();
southLayout = new BorderLayout();
southPanel.setLayout(southLayout);
//set radio buttons and format layouts
radioOrderPanel = new JPanel();
radioOrderPanel.setLayout(new BoxLayout(radioOrderPanel, BoxLayout.Y_AXIS));
radioSortPanel = new JPanel();
radioSortPanel.setLayout(new BoxLayout(radioSortPanel, BoxLayout.Y_AXIS));
radioColorPanel = new JPanel();
radioColorPanel.setLayout(new BoxLayout(radioColorPanel, BoxLayout.Y_AXIS));
//define radio buttons
rOB1 = new JRadioButton("Random Order", true);
rOB1.addActionListener(buttonListener);
radioOrderPanel.add(rOB1);
rOB2 = new JRadioButton("In Order", false);
rOB2.addActionListener(buttonListener);
radioOrderPanel.add(rOB2);
rOB3 = new JRadioButton("In Reverse", false);
rOB3.addActionListener(buttonListener);
radioOrderPanel.add(rOB3);
rSB1 = new JRadioButton("Bubble Sort", true);
rSB1.addActionListener(buttonListener);
radioSortPanel.add(rSB1);
rSB2 = new JRadioButton("Insertion Sort", false);
rSB2.addActionListener(buttonListener);
radioSortPanel.add(rSB2);
rSB3 = new JRadioButton("Merge Sort", false);
rSB3.addActionListener(buttonListener);
radioSortPanel.add(rSB3);
rSB4 = new JRadioButton("Quick Sort", false);
rSB4.addActionListener(buttonListener);
radioSortPanel.add(rSB4);
rCB1 = new JRadioButton("Green", true);
rCB1.addActionListener(buttonListener);
radioColorPanel.add(rCB1);
rCB2 = new JRadioButton("Red", false);
rCB2.addActionListener(buttonListener);
radioColorPanel.add(rCB2);
rCB3 = new JRadioButton("White", false);
rCB3.addActionListener(buttonListener);
radioColorPanel.add(rCB3);
rCB4 = new JRadioButton("Blue", false);
rCB4.addActionListener(buttonListener);
radioColorPanel.add(rCB4);
//add radio buttons to a button group
orderGroup = new ButtonGroup();
orderGroup.add(rOB1);
orderGroup.add(rOB2);
orderGroup.add(rOB3);
sortGroup = new ButtonGroup();
sortGroup.add(rSB1);
sortGroup.add(rSB2);
sortGroup.add(rSB3);
sortGroup.add(rSB4);
colorGroup = new ButtonGroup();
colorGroup.add(rCB1);
colorGroup.add(rCB2);
colorGroup.add(rCB3);
colorGroup.add(rCB4);
initialPanel.add(southPanel, BorderLayout.NORTH);
picture.paint(picture.getGraphics());
mainFrame.setVisible(true);
}
// this object is triggered whenever a button is clicked
private class ButtonActionListener implements ActionListener {
public void actionPerformed(ActionEvent event) {
// find out which button was clicked
Object source = event.getSource();
// start sort button was clicked
if (source == sortButton) {
// call the sort
doBubblesort();
}
// called when user hits return in text field
if (source == arraySizeTextField) {
int size = Integer.parseInt(arraySizeTextField.getText());
}
}
}
private void doBubblesort() {
int temp;
// this is just bubblesort
for (int i=0; i<limit-1; i++) {
for (int j=0; j<limit-1-i; j++) {
if (array[j]>array[j+1]) {
temp = array[j]; array[j] = array[j+1]; array[j+1] = temp;
// redraw only locations j and j+1
doPaint = PaintType.SINGLE; // try changing this to ALL and see what happens
index = j;
picture.paint(picture.getGraphics());
index = j+1;
picture.paint(picture.getGraphics());
}
}
}
}
class SortCanvas extends Canvas {
// this class paints the sort bar
SortCanvas() {
setSize(pictureWidth, pictureHeight);
setBackground(Color.white);
}
public void paint(Graphics g) {
if (doPaint == PaintType.ALL) {
// paint whole array - this takes time so it shouldn't be done too frequently
setBackground(Color.white);
g.setColor(Color.white);
g.fillRect(0, 0, pictureWidth, pictureHeight);
for (int i=0; i<limit; i++) {
// the larger the number, the brighter green it is
// green is between 0.0 and 1.0
// divide by the largest number to get a value between 0 and 1
float green = (float)(array[i]/(float)largestNum);
// clamp if necessary - it shouldn't be
if (green<0f) green = 0f;
if (green>1f) green = 1f;
g.setColor(new Color(0.0f, green, 0.0f));
// array location 0 is painted at left;
// array location limit-1 is painted to right
//this is a single vertical line in the bar
g.drawLine((int)(i*pictureWidth/limit), 0,
(int)(i*pictureWidth/limit), pictureHeight);
}
}
else {
// just paint one location on the bar
float green = (float)(array[index]/(float)largestNum);
if (green<0f) green = 0f;
if (green>1f) green = 1f;
g.setColor(new Color(0.0f, green, 0.0f));
g.drawLine((int)(index*pictureWidth/limit), 0,
(int)(index*pictureWidth/limit), pictureHeight);
}
}
}
}

This is not required;
picture.paint(picture.getGraphics());
getGraphics will return null if the component has not yet being painted itself. You should avoid using this method, it is simply a snap shot of the current components graphical state (which in your case is nothing)
You don't control the paint process, that's down to the repaint manager. You can request updates via the repaint methods. Have a read through Painting in AWT and Swing
You should avoid mixing heavy weight (Canvas) & light weight components (JFrame) together, where possible, you should stick with Swing components

Calling paint() directly can lead to unexpected behavior as you are see from this, use repaint() instead:
picture.repaint();

Dynamically adding components to JPanel

I'm trying to dynamically add some components to a JPanel, but unfortunatelly they don't appear. I only see the ones added in the constuctor.
Updated version (adding a new JPanel, where all the components will be):
public class View extends JPanel {
JPanel panel = new JPanel();
JLabel label;
JLabel labels[];
JButton b1 = new JButton("OK");
public View() {
this.setLayout(new FlowLayout());
this.add(panel); // adding a new JPanel
label = new JLabel("My label");
panel.add(label); // adding label to the new panel (this one works)
}
public void showLabels() {
System.out.println("function showLabels called");
labels = new JLabel[5];
for (int i = 0; i < 5; i++) {
labels[i] = new JLabel("Label: " + i);
panel.add(labels[i]); // this one doesn't work
}
panel.add(b1); // this one doesn't work, too
this.validate(); // validating this class (parent container)
panel.validate(); // validating the panel, where all the components are
}
}
Unfortunatelly nothing changed.

Call validate() on the parent container, as shown in the Nested Layout Example. Those labels on the lower left are added dynamically. Note that calling pack() might cause the size of the GUI to change, whereas calling validate() won't. If you need to get the GUI to resize - call pack(), else call validate().

How to embed a grid layout inside a border layout in java

I have a border layout and I want to add a grid layout to the center section. However, I can't declare a grid and then add my center border. How can I do this?
public Liability_Calculator(String s)
{
super(s);
setSize(325,200);
c = getContentPane();
c.setLayout(new BorderLayout());
//the top label
total = new JLabel("Total monthly liabilities ", JLabel.CENTER);
c.add(total, BorderLayout.NORTH);
//the grid
GridLayout grid = new GridLayout(2,2);
text_field1 = new JTextField(7);
//I GET AN ERROR HERE!!!!!!!
grid.add(text_field1);
//AND ERROR HERE!!!!!!!!!!!!!
c.add(grid, BorderLayout.CENTER);
setVisible(true);
}

You're trying to add a component to a layout, and that simply cannot be done. Instead use a JPanel, give it a GridLayout, and then add the component to the JPanel (acting as the "container" here).
In general, you will want to nest JPanels with each using the best layout for the GUI, here the inner JPanel using GridLayout and the outer one using BorderLayout. Then you simply add the inner JPanel to the outer one (here your contentPane) in the BorderLayout.CENTER position.

Providing code visualization derived from Hovercraft's answer:
Display class:
public class Display extends JFrame {
JPanel gridHolder = new JPanel(); // panel to store the grid
private GridLayout buttonsGrid; // space containing a buttons
private JButton myButtons[]; // grid is to be filled with these buttons
private BorderLayout mainGUILayout; // main gui layout
private Container mainGuiContainer;
public Display() {
mainGUILayout = new BorderLayout(5,5); // Border layout option
mainGuiContainer = getContentPane(); // getting content pane
mainGuiContainer.setLayout(mainFrameLayout); // setting main layout
buttonsGrid = new GridLayout(4, 1, 5, 5); // 4 buttons one over the other
myButtons = new JButton[4]; // player's hand represented with buttons
gridHolder.setLayout(buttonsGrid);
for (int x = 0; x < 4; x++) {
myButtons[x] = new JButton (" ");
gridHolder.add(myButtons[x]); }
add(gridHolder, BorderLayout.WEST);
setVisible(true); } }
MainGUILaunch class:
public class MainGUILaunch {
public static void main (String args[]) {
Display myApplication = new Display();
myApplication.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myApplication.setSize(1024, 1024);
myApplication.setVisible(true); // displaying application }
} // End of MainGUILaunch