JButton buttonArray[][] = new JButton [6][7];
JPanel grid;
JButton b1;
grid.setLayout (new GridLayout(6,7,0,0));
slot = new ImageIcon ("gameboard.png");
for (int i = 0; i < 6; ++i)
{
for (int j = 0; j < 7; ++j)
{
b1 = new JButton (slot);
buttonArray[i][j] = b1;
buttonArray[i][j].setContentAreaFilled (false);
buttonArray[i][j].setBorderPainted (false);
grid.add(buttonArray[i][j]);
}
}
I am getting a NullPointerException which points to the grid.setLayout (new GridLayout(6,7,0,0)); part and to the new GameBoard(); which is in the main method at the bottom.
I add grid panel t o another panel as well, together with other panels:
panel = new JPanel();
panel.setLayout(new BorderLayout());
panel.add("North", panel1);
panel.add("Center",grid);
panel.add("South",panel2);
add(panel);
I did initialize grid and buttonArray[][] already. What am I missing?
The grid variable is null as it has never been assigned an object. You need to either give it a new something or pass in its value via a setter method or constructor parameter.
More important than the actual solution to your current problem, is the knowledge of how to debug most common NullPointerExceptions. When you encounter a NullPointerException, you should carefully check all the variables on the line that throws the exception, find out which one is null, and then track back in your program to find out why it's null when you though otherwise.
You didn't initialize the grid variable:
JPanel grid; // null since it wasn't initialized
JButton b1;
grid.setLayout (new GridLayout(6,7,0,0));
You should just create some object there:
JPanel grid = new JPanel();
JButton b1;
grid.setLayout (new GridLayout(6,7,0,0));
Related
So i'm creating an array of buttons that is supposed to display and 8,8 grid, instead it displays very small buttons spreading across the window (31 buttons in a row for two rows then two more buttons on the third). If I replace:
gamePanel1.add(buttons[a][b]);
with:
frame.add(buttons[a][b]);
... it display correctly but when initialising the array, I have to resize the window to see the buttons as it does not fit to contents.
Here is the code to create the buttons:
contentPane.setLayout(new BorderLayout());
JPanel gamePanel1 = new JPanel();
buttons = new JButton[boardsize][boardsize];
mineBoard = new int[9][9];
for (int a = 0; a < boardsize; a++)
for (int b = 0; b < boardsize; b++) {
buttons[a][b] = new JButton("");
buttons[a][b].setBounds(30+gridsize*a,30+gridsize*b,gridsize,gridsize);
gamePanel1.add(buttons[a][b]);
buttons[a][b].addMouseListener(new MouseListener(a,b));
setx(a);
sety(b);
settried(false);
setmine(false);
}
contentPane.add(gamePanel1, BorderLayout.CENTER);
Can anyone tell me how I might fix this or show me how with this code I may use a different layout - i tried grid layout for the buttons but could not get it working at all.
First create a Panel as:
JPanel panel=new JPanel();
Then set the layout as
panel.setLayout(new GridLayout(8,8));
Then using a for loop create and add the buttons and the buttons will be displayed in eight by eight grid. Thanks.
I'm creating a simple Minesweeper game in Java. Size 9x9.
I create an array of JPanels and an array of buttons; I add each button to its respective JPanel. then i add the JPanels to the JFrame.
How do i distinguish between each button on the action event?
Here's some of my code:
int gridx = 9;
int gridy = 9;
JButton[] buttons = new JButton[gridx*gridy];
JPanel[] jpanels = new JPanel[gridx*gridy];
public Minesweeper(){
super("Minesweeper");
setLayout(new GridLayout(9,9));
JPanel panel = new JPanel();
int i = 0;
for(i = 0; i<gridx*gridy; i++){
jpanels[i] = new JPanel();
buttons[i] = new JButton();
buttons[i].addActionListener(buttonEvent);
jpanels[i].setLayout(new GridLayout(1,1));
jpanels[i].add(buttons[i]);
add(jpanels[i]);
}
//buttons[67].setEnabled(false);
setSize(300,300);
setVisible(true);
}
The only way i can think about doing this is adding text to the button like so:
buttons[i] = new JButton(i);
Then calling getActionCommand() but i dont want text to show up on the button. Any other ideas?
You can use AbstractButton#setActionCommand.
In your loop:
buttons[i].setActionCommand(i+"");
Then you'll get i back when you use getActionCommand
Note I did mention in a comment on another answer that I would create a new class Mine which extends JButton which I believe to be a better and more complete solution. This however gets the job done rather quickly.
I'm relatively new to java and i'm trying to do an assignment for school. In my assignment i'm supposed to make a GUI program that makes a 8 by 8 red and black colored checkerboard. The only problem (so far) that i'm having is initializing a two-dimensional array of JPanels. i'm getting this error when using eclipse:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 7
This doesn't give an error until i try to run the code. It says the error is occurring in the body of this for loop:
JPanel[][] panel = new JPanel[7][7];
for (int i = 0; i <= panel.length; i++){
panel[i][0] = new JPanel();
panel[i][1] = new JPanel();
panel[i][2] = new JPanel();
panel[i][3] = new JPanel();
panel[i][4] = new JPanel();
panel[i][5] = new JPanel();
panel[i][6] = new JPanel();
panel[i][7] = new JPanel();
}
This does work if i don't use a for loop but i really don't want to put in 64 different statements do do this. I double checked and the panel.length does give the value 7 (which is what i wanted) and did not work even when i physically put in 7. I don't have any syntax error is my code, but i still get the error. Is there some other way i should go about doing this? Thanks in advance. Remember i'm new to this.
"make a GUI program that makes a 8 by 8 red and black colored checkerboard. The only problem (so far) that i'm having is initializing a two-dimensional array of JPanels.".
If all you need to do is make the board, with no other conditions, why not just use a GridLayout
JPanel mainPanel = new JPanel(new GridLayout(8, 8));
for (int i = 0; i < 64; i++){
JPanel panel = new JPanel();
// alternate background colors with a predefined boolean and an if
mainPanel.add(panel);
}
Three things:
A checkboard is 8×8, so you really want panel.length to be 8, no?
A standard for loop uses < for the test, not <=.
If you use two nested loops, you don't need to repeat new JPanel() 8 times.
Result:
JPanel[][] panel = new JPanel[8][8];
for (int i = 0; i < panel.length; i++) {
for (int j = 0; j < panel[i].length; j++) {
panel[i][j] = new JPanel();
}
}
Why do I get an error when I try to set the ImageIcon of this JLabel to something. It returns a null pointer exception. Does anyone know the problem?
public class Window extends JFrame{
JPanel panel = new JPanel();
JLabel stick[] = new JLabel[10];
Window(){
super("ThisIsWindow");
setSize(650,550);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setResizable(false);
add(panel);
panel.setLayout(null);
stick[5].setIcon(new ImageIcon("stick.gif"));
}
}
The error occurs on the last line of code that sets stick[5] to stick.gif. Can anyone help?
Add
stick[5] = new JLabel();
before
stick[5].setIcon(new ImageIcon("stick.gif"));
Basically, you are creating an array that holds 10 references of type JLabel, and those references are referring to nothing (null) at the beginning:
JLabel stick[] = new JLabel[10];
So you need to create 10 instances of JLabel with new JLabel() and let those 10 references pointing to them:
for(int i = 0; i < 10; i++) stick[i] = new JLabel();
Is there a JLabel object in stick[5]?
I am dynamically generating a list of name boxes, sliders and labels, and am trying to figure out how to access the values of the sliders and change the labels. Other posts suggest using an array, but I have no idea where to begin with that.
My code is as such:
public Tailoring(int n) {
/*initComponents();*/
JPanel containerPanel = new JPanel();
containerPanel.setLayout(new BoxLayout(containerPanel, BoxLayout.PAGE_AXIS));
this.add(containerPanel);
JLabel Title = new JLabel("Tailoring:");
containerPanel.add(Title);
for(int i = 0; i < n; i++){
JPanel rowPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
JTextField NameBox = new JTextField("Guest " + (i+1));
JSlider TipSlider = new JSlider();
JLabel TipCost = new JLabel();
rowPanel.add(NameBox);
rowPanel.add(TipSlider);
rowPanel.add(TipCost);
containerPanel.add(rowPanel);
}
}
You can create a new class YourPanel which extends JPanel.
Instead of the statement
JPanel rowPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
you can use
YourPanel rowPanel = new YourPanel(new FlowLayout(FlowLayout.LEFT));
Define textfield, slider and label as the properties of this YourPanel class.
Provide getters/setters for each field. Then use an array or ArrayList of YourPanel objects in your application. You will be able to reach the nth panel's label with a call like:
panels.get(n).getJLabel();
It appears that you'd like to change the value displayed in the JLabel when the associated JSlider is modified, right? The best way to associate pairs of objects in Java is with a Map structure:
Map<Component, JSlider> sliderToLabel = new HashMap<Component, JSlider>();
for (int i = 0; i < n; i++) {
// after your loop code
sliderToLabel.put(TipSlider, TipCost); // map the slider to its label
}
You will be able to get a reference to the JSlider in the code that listens for changes on that component.
JLabel updateLabel = sliderToLabel.get(targetedSlider);
updateLabel.setText("updated text");
Notes
As a matter of convention, variable names should begin with lower case letters
The event listener I alluded to should also be attached in the loop. See Writing Event ListenersOracle