Thread: Set Variable In Event Handler

I have a class variable, that I want to set in a separate class. I am instantiating an instance of this class in my second class, and referencing and setting the variable. If I use a message box to show the value of the variable in the EventHandler the value is set. However, when I try to access the value from my 'main' class Data the value is empty.

How should I re-write the below code so the value of playerSelected remains set?

import javax.swing.*;
import java.awt.event.*;
import javax.swing.border.LineBorder;
import java.awt.*;
 
public class Data {
 
    JFrame frame		= new JFrame();
    JPanel mainPanel	= new JPanel();
    JPanel secondPanel  = new JPanel();
 
    String playerSelected;
    String playerimage;
    String cpuimage;
    String BattlesWon = "0";
    String BattlesLost = "0";
    String Gold = "0";
    String PlayerLevel = "1";
 
    public static void main(String args[]) {
        new Data().start();
    }
 
    public void start() {
        JLabel myLabel = new JLabel("Enter Player Name:");
        JPanel pnlHeaderInfo = new JPanel(); 
        JPanel pnlCharacters = new JPanel();
        JPanel pnlNextButton = new JPanel();
 
        JTextField myText = new JTextField(20); 
        myLabel.setAlignmentX(JTextField.CENTER_ALIGNMENT);
 
        pnlHeaderInfo.setPreferredSize(new Dimension(300, 60));
        pnlHeaderInfo.setLayout(new FlowLayout());
        pnlHeaderInfo.add(myLabel);
        pnlHeaderInfo.add(myText);
        pnlHeaderInfo.setBorder(new LineBorder(Color.RED, 3));
        mainPanel.setPreferredSize(new Dimension(600, 400));
        mainPanel.add(pnlHeaderInfo);
 
        JLabel lblLeftChar1 = new JLabel();
        JLabel lblCenterChar2 = new JLabel();
        JLabel lblRightChar3 = new JLabel();
 
        MyMouseHandler myMouseHandler = new MyMouseHandler();
 
        lblLeftChar1.setMinimumSize(new Dimension(141,244));
        lblLeftChar1.setMaximumSize(new Dimension(141,244));
        lblLeftChar1.setName("Link");
        lblLeftChar1.setIcon(new ImageIcon(getClass().getResource("/resources/__Link.jpg")));
        lblLeftChar1.addMouseListener(myMouseHandler);
 
        lblCenterChar2.setMinimumSize(new Dimension(141,244));
        lblCenterChar2.setMaximumSize(new Dimension(141,244));
        lblCenterChar2.setName("Mario");
        lblCenterChar2.setIcon(new ImageIcon(getClass().getResource("/resources/__Mario.png")));
        lblCenterChar2.addMouseListener(myMouseHandler);
 
        lblRightChar3.setMinimumSize(new Dimension(141,244));
        lblRightChar3.setMaximumSize(new Dimension(141,244));
        lblRightChar3.setName("Pikachu");
        lblRightChar3.setIcon(new ImageIcon(getClass().getResource("/resources/__Pikachu.png")));
        lblRightChar3.addMouseListener(myMouseHandler);
 
        pnlCharacters.setPreferredSize(new Dimension(496, 256));
        pnlCharacters.setLayout(new BorderLayout());
 
        pnlCharacters.add(lblLeftChar1, BorderLayout.LINE_START);
        lblCenterChar2.setHorizontalAlignment(JLabel.CENTER);
        pnlCharacters.add(lblCenterChar2, BorderLayout.CENTER);
        pnlCharacters.add(lblRightChar3, BorderLayout.LINE_END);
        pnlCharacters.setBorder((new LineBorder(Color.BLUE, 3)));
        mainPanel.add(pnlCharacters);
 
        //JOptionPane.showMessageDialog(null, playerSelected, "TITLE", JOptionPane.WARNING_MESSAGE);
 
        JButton btnNext = new JButton("Start Game");
        btnNext.addActionListener(new ActionListener() {
 
            @Override
            public void actionPerformed(ActionEvent e) {
                //hide the current main panel
                mainPanel.setVisible(false);
                beginstagetwo();
            }
        });
 
        btnNext.setMinimumSize(new Dimension(112,29));
        btnNext.setMaximumSize(new Dimension(112,29));
        pnlNextButton.add(btnNext, BorderLayout.CENTER);
        pnlNextButton.setBorder((new LineBorder(Color.GREEN)));
        mainPanel.add(pnlNextButton);
 
        frame.add(mainPanel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        frame.pack(); 
        frame.setLocationRelativeTo(null); 
        frame.setVisible(true);
    }
 
    public void beginstagetwo() {
        JPanel pnlPlayerStats = new JPanel();
 
        pnlPlayerStats.setPreferredSize(new Dimension(300, 60));
 
        JLabel lblPlayerName = new JLabel("Player Name:");
        JTextField txtPlayerName = new JTextField(30);
        txtPlayerName.setText(playerSelected);
        lblPlayerName.setAlignmentX(JTextField.CENTER_ALIGNMENT);
 
        JLabel lblPlayerGold = new JLabel("Gold:");
        JTextField txtPlayerGold = new JTextField(6);
        lblPlayerGold.setAlignmentX(JTextField.CENTER_ALIGNMENT);
 
        pnlPlayerStats.setLayout(new FlowLayout());
        pnlPlayerStats.add(lblPlayerName);
        pnlPlayerStats.add(txtPlayerName);
        pnlPlayerStats.add(lblPlayerGold);
        pnlPlayerStats.add(txtPlayerGold);
 
 
        pnlPlayerStats.setBorder(new LineBorder(Color.ORANGE, 3));
        secondPanel.setPreferredSize(new Dimension(600, 400));
        secondPanel.add(pnlPlayerStats);
        frame.add(secondPanel);
        frame.pack();
        frame.setVisible(true);
    }
}
class MyMouseHandler extends MouseAdapter {
 
    Data dt = new Data();
 
    @Override
    public void mouseClicked(MouseEvent evt) {
        JLabel source = (JLabel) evt.getSource();
        String labelname = source.getName();
        dt.playerSelected = labelname;
    }
 
}

Or don't make an instance at al and call the classvariable direct.
YourClass.variable

Originally Posted by Norm

The instance of Data created in the listener class is different from the instance created in the main method. Each instance has its own version of the playerSelected variable.
One solution is to pass a reference to the one and only instance of the Data class to the listener class's constructor and save that reference in the listener class. Code in the Data class would use the this variable to reference to its instance.

I am new to JAVA - can you provide an example of this?

Originally Posted by Norm

@ufotje
That only works if the variable is static. Not a recommended solution.

Why do you recommend against setting the variable as static?

Originally Posted by jo15765

I am new to JAVA - can you provide an example of this?

class MyMouseHandler extends MouseAdapter {
    private Data dt;
 
    //Add Constructor
    class MyMouseHandler(Data data){
        dt = data;
    }
 
    //Add Getter
    public Data getData(){
        return data;
    }
 
    @Override
    public void mouseClicked(MouseEvent evt) {
        JLabel source = (JLabel) evt.getSource();
        String labelname = source.getName();
        dt.playerSelected = labelname;
    }
 
}

I get a compile error of Duplicate Class: MyMouseHandler when I add this line in

//Add Constructor
    class MyMouseHandler(Data data){
        dt = data;
    }

Originally Posted by jo15765

I get a compile error of Duplicate Class: MyMouseHandler when I add this line in

//Add Constructor
    class MyMouseHandler(Data data){
        dt = data;
    }

Sorry my bad it should be:

public MyMouseHandler(Data data){
    ...
}

And I am assuming I will have to update how I call it? I am getting this compile error

Error:(45, 41) java: constructor MyMouseHandler in class MyMouseHandler cannot be applied to given types;
  required: Data
  found: no arguments
  reason: actual and formal argument lists differ in length

Originally Posted by Norm

@ufotje Please read:
http://www.javaprogrammingforums.com...n-feeding.html

You have written all the OPS code for him without letting him work through the details and learn as he goes.

Lol apperently not, otherwise he wouldn't have run in to that error...

--- Update ---

Originally Posted by jo15765

And I am assuming I will have to update how I call it? I am getting this compile error

Error:(45, 41) java: constructor MyMouseHandler in class MyMouseHandler cannot be applied to given types;
  required: Data
  found: no arguments
  reason: actual and formal argument lists differ in length

No offence, but if you have to ask something like this, I would start with following some basic java tutorials before starting on a swing app

--- Update ---

Originally Posted by jo15765

Why do you recommend against setting the variable as static?

The message disapeard after editting so...
They're hard to control, anything or anyone could modify them and they can have any state at any time.
The general rule is how smaller the scope, the better and how easier to control

I have my code as the below, where I declare the variable in my Data class, and from what I know, passing variable to the MouseEvent class. However, my JLabel prompt still shows empty?

public void start() {
        Data data = new Data();
 
        MyMouseHandler myMouseHandler = new MyMouseHandler(data);
 
        JOptionPane.showMessageDialog(null, this.playerSelected, "TITLE", JOptionPane.WARNING_MESSAGE);
    }
 
    class MyMouseHandler extends MouseAdapter {
 
    private Data dt;
 
    //Add Constructor
    public MyMouseHandler(Data data){
        dt = data;
    }
 
    //Add Getter
    public Data getData(){
        return dt;
    }
 
    @Override
    public void mouseClicked(MouseEvent evt) {
        JLabel source = (JLabel) evt.getSource();
        String labelname = source.getName();
        dt.playerSelected = labelname;
    }
 
}

Originally Posted by Norm

How many instances of the Data class are created? It looks like one in the main method and another in the start method. Don't create a second instance, use the current one.Use the this variable to reference the current instance.

If I try to use the variable this like below

Data this.data;

I get errors of

Error:(25, 9) java: not a statement
Error:(25, 13) java: ';' expected
Error:(25, 19) java: not a statement

What did you expect? You create a new Data with the default constructor, which takes no parameters.
So every instance variable Data has is still null.
Of cource you need to set the value's first.
Make a constructor for Data that takes the arguments or provide setter methods

--- Update ---

Originally Posted by jo15765

If I try to use the variable this like below

Data this.data;

I get errors of

Error:(25, 9) java: not a statement
Error:(25, 13) java: ';' expected
Error:(25, 19) java: not a statement

The middle one is easy: go to line 25 of your code and add an ; where it's missing?
for the other two, what is line 25 of your code?
What idea are you using? It should warn you for stuff like that...

--- Update ---

And the prob isn't with your Data it's your JLabel, since you're using that to set the String labelName
From what I understand from your question I think you're trying to do something like this:

source.setText(data.getName());