Develop Reference

java communication between 2 JFrames

I'm getting an AWT-EventQueue-0 Null Pointer Exception in the below code and I can't get to fix it.
I want to have a main frame, from which by pressing a button
I open a second frame, where I have the option to create new players,
which would show up in the main frame.
I passed the references to the constructors, but I still keep getting the error.
I would be very happy for some help, thanks!
public class Main {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new App();
}
});
}
}
public class App extends JFrame {
private MainPanel mainPanel;
private SecondPanel secondPanel;
public App() {
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(800, 600);
secondPanel = new SecondPanel(mainPanel);
mainPanel = new MainPanel(secondPanel);
add(mainPanel);
}
}
public class MainPanel extends JPanel {
private JTextArea textArea;
private JScrollPane scrollPane;
private JButton options;
public MainPanel(SecondPanel secondPanel) {
textArea = new JTextArea();
textArea.setColumns(20);
textArea.setRows(5);
textArea.setSize(300, 300);
textArea.setVisible(true);
textArea.setEditable(false);
scrollPane = new JScrollPane(textArea);
scrollPane.setSize(new Dimension(400, 400));
options = new JButton("Options");
options.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
secondPanel.setVisible(true);
}
});
add(scrollPane);
add(options);
}
public JTextArea getTextArea() {
return textArea;
}
public void setTextArea(JTextArea textArea) {
this.textArea = textArea;
}
}
public class SecondPanel extends JFrame {
private JButton create, remove;
private JPanel panel;
public SecondPanel(MainPanel mainPanel) {
setVisible(false);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(400, 400);
panel = new JPanel();
panel.setLayout(new BorderLayout());
create = new JButton("create");
create.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
mainPanel.getTextArea().append("New Player Created");
}
});
remove = new JButton("remove");
remove.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
mp.getTextArea().setText("Player removed");
}
});
add(panel);
panel.add(create, BorderLayout.EAST);
panel.add(remove, BorderLayout.WEST);
}
}

Well, it has to be "null", because you don't initialise your MainPanel before you hand it over to the secondPanel.
Instead, make an own method for setting the MainPanel on the secondPanel and to set the secondPanel on the MainPanel.
I see that you need the secondPanel for instance in your constructor to set an ActionListener. Do that in your "setSecondPanel(SecondPanel sPanel)"-Method which, as I mentioned before, you should create.

how to identify dynamically created jbutton actions

I create two jbuttons in one panel(can be Box).i create same panel dynamically several times in same frame.so if two panels created dynamically those button make with same variable name.But i want to identify buttons one by one for put actions.how to identify dynamically created buttons one by one?
button creating code
public class Jscrollpanetest extends JFrame {
JScrollPane scrollPane;
Box box;
private static int panelCount = 0;
public Jscrollpanetest() {
setPreferredSize(new Dimension(200, 400));
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
scrollPane = new JScrollPane();
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
scrollPane.getVerticalScrollBar().setUnitIncrement(15);
box = Box.createVerticalBox();
scrollPane.getViewport().add(box);
this.add(scrollPane);
this.pack();
this.setLocationRelativeTo(null);
this.setVisible(true);
Timer t = new Timer(1000, new ActionListener() {
public void actionPerformed(ActionEvent ae) {
box.add(new TestPanel(), box.size());
scrollPane.validate();
}
});
t.setRepeats(true);
t.start();
}
public class TestPanel extends JPanel {
int myId = panelCount++;
public TestPanel() {
this.setLayout(new GridBagLayout());
this.setBorder(BorderFactory.createBevelBorder(1));
JButton up = new JButton("^");
JLabel rate = new JLabel("1");
JButton down = new JButton("^");
JLabel label = new JLabel("" + myId);
label.setHorizontalAlignment(JLabel.CENTER);
label.setVerticalAlignment(JLabel.CENTER);
this.setMaximumSize(new Dimension(1000, 200));
this.setPreferredSize(new Dimension(1000, 100));
this.add(label);
this.add(up);
this.add(rate);
this.add(down);
}
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
Jscrollpanetest testScrollPane = new Jscrollpanetest();
}
});
}
}

If use and dynamic created ActionListener there will be no problem. So each button will have its own ActionListener.
If using a common ActionListener must add tags to each button as extend JButton.

How to dynamically add JLabels to JPanel?

I'm having a problem with this. I have a JPanel and normally I would create a JLabel like this:
JLabel lblNewLabel = new JLabel("New label");
lblNewLabel.setBounds(0, 0, 135, 14);
panel.add(lblNewLabel);
but I want each time I click a button, in that panel to be created a new JLabel with the same size, but with a different height possition. I tried:
panel.add(new JLabel(stringName));
but this way I don't get to set it's bounds. stringName I get from a JTextField.

First off, use a layout. Done correctly the layout will place the components like you want. Secondly, when dynamically adding a component to a layout you need to tell the layout to update. Here is an example, it adds a label each time a button is pressed:
public static void main(String[] args) {
final JFrame frame = new JFrame("Test");
frame.setLayout(new GridLayout(0, 1));
frame.add(new JButton(new AbstractAction("Click to add") {
#Override
public void actionPerformed(ActionEvent e) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
frame.add(new JLabel("Bla"));
frame.validate();
frame.repaint();
}
});
}
}));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 300);
SwingUtilities.invokeLater(new Runnable() {
#Override public void run() {
frame.setVisible(true);
}
});
}

As said by #AndrewThompson use a correct LayoutManager, you should not be messing with setBounds etc.
Here is an example I made (Simply adds a JLabel to the JPanel each time the JButton is clicked):
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class Test {
public Test() {
createAndShowUI();
}
private void createAndShowUI() {
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
initComponents(frame);
frame.setResizable(false);
frame.pack();
frame.setVisible(true);
}
private void initComponents(final JFrame frame) {
final JPanel panel = new JPanel();
JButton button = new JButton("Add label");
button.addActionListener(new ActionListener() {
int count = 1;
#Override
public void actionPerformed(ActionEvent e) {
JLabel _lbl = new JLabel("Label " + count);//make label and assign text in 1 line
panel.add(_lbl);//add label we made
panel.revalidate();
panel.repaint();
frame.pack();//so our frame resizes to compensate for new components
count++;
}
});
frame.add(panel, BorderLayout.CENTER);
frame.add(button, BorderLayout.SOUTH);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Test();
}
});
}
}

Try swapping the order of of your commands, add the panel first then set the location.

How do I add a class in to a JPanel?

This is the JPanel
public class DisplayBoard {
public static void main (String[] args) {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//The main panel
JPanel main = new JPanel();
main.setPreferredSize(new Dimension(600,800) );
main.setLayout(new BorderLayout());
//The title panel
JPanel title = new JPanel();
title.setPreferredSize(new Dimension(400, 120));
title.setBackground(Color.YELLOW);
JLabel test1 = new JLabel("Title goes here");
title.add(test1);
//The side bar panel
JPanel sidebar = new JPanel();
sidebar.setPreferredSize(new Dimension(200, 800));
sidebar.add(AddSubtract);
sidebar.setBackground(Color.GREEN);
JLabel test2 = new JLabel("Sidebar goes here");
sidebar.add(test2);
//The panel that displays all the cards
JPanel cardBoard = new JPanel();
cardBoard.setPreferredSize(new Dimension(400,640) );
//adding panels to the main panel
main.add(cardBoard, BorderLayout.CENTER);
main.add(title, BorderLayout.NORTH);
main.add(sidebar, BorderLayout.WEST);
frame.setContentPane(main);
frame.pack();
frame.setVisible(true);
}
}
and I want to add this class into the sidebar panel
public class AddSubtract {
int Number = 0;
private JFrame Frame = new JFrame("Math");
private JPanel ContentPane = new JPanel();
private JButton Button1 = new JButton("Add");
private JButton Button2 = new JButton("Subtract");
private JLabel Num = new JLabel ("Number: " + Integer.toString (Number));
public AddSubtract() {
Frame.setContentPane(ContentPane);
ContentPane.add(Button1);
ContentPane.add(Button2);
ContentPane.add(Num);
Button1.addActionListener(new Adding());
Button2.addActionListener(new Subtracting());
}
public class Adding implements ActionListener {
public void actionPerformed(ActionEvent e) {
Number++;
Num.setText ("Number: " + Integer.toString (Number));
}
}
public class Subtracting implements ActionListener {
public void actionPerformed(ActionEvent e) {
Number--;
Num.setText ("Number: " + Integer.toString (Number));
}
}
public void launchFrame(){
Frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Frame.pack();
Frame.setVisible(true);
}
public static void main(String args[]){
AddSubtract Test = new AddSubtract();
Test.launchFrame();
}
}
Can someone explain to me how I can do this ?
I have a feeling that this is not going to work, but I really want to learn the way to do it.

This definately is not going to work. For starters, you have two main() methods. Second, if you want to add a class to your Frame, it should extend from JComponent. Basically, your code should look like this:
public class MainFrame extends JFrame {
public MainFrame() {
this.add(new MainPanel())
//insert all settings here.
}
}
public class MainPanel extends JPanel {
public MainPanel() {
this.add(new AddSubtract());
this.add(/*more panels*/)
}
}
public class AddSubtract extends JPanel {
public AddSubtract() {
//add buttons and stuff here
}
}
and variables do NOT start with capitals.
Edit: And when you have some JFrame, it's usually best to have a main() method with just one line:
public static void main(String[] args) {
new MainFrame();
}
just set the settings and configuration of the JFrame in the constructor.

adding new jpanel with default components in swing

can any one tell me how to add a panel in a jtabbedPane whenever i am clicking on a "add" button.Its like google chrome new tab.But the thing is ,the generated panel must contains some default components.Thanks in advance.

Please see the code below. It shows you how to do what you need.
public class DemoApp {
private JTabbedPane tabPane = new JTabbedPane();
public DemoApp() {
initComponents();
}
private void initComponents() {
JFrame frame = new JFrame("Test");
frame.setSize(500, 400);
frame.setLocationRelativeTo(null);
JPanel panel = new JPanel();
panel.setLayout(new BorderLayout());
frame.getContentPane().add(panel);
JButton btn = new JButton("Add panel");
btn.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
int index = tabPane.getTabCount() + 1;
JPanel newPanel = new JPanel();
newPanel.setLayout(new FlowLayout());
newPanel.add(new JLabel("Panel " + index));
tabPane.addTab("Tab " + index, newPanel);
}
});
panel.add(tabPane, BorderLayout.CENTER);
panel.add(btn, BorderLayout.SOUTH);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
public static void main(String[] args) {
new DemoApp();
}
}