JCheckBox的ItemListener不起作用

Question

I'm just a beginner and I'm having a problem with implementing an item listener as an inner class.

What I want to happen is that if someone selects the checkbox t1 , the text above it, written in the TextArea txtTop , becomes bold.

However, Eclipse tells me that there are multiple problems with my listener.

1. It wants me to declare t1 and txtTop as final.
2. It wants me to not make the listener class private.
3. It doesn't find the listener anyway. The line t1.addItemListener(new cl()); doesn't work.

So yeah, I don't know what to do. Hopefully one of you can help me out! :)

Here is the code:

import java.awt.BorderLayout;


public class WindowBuilderTest extends JFrame 
{

private JPanel contentPane;


//Launch the application.
public static void main(String[] args) 
{
    EventQueue.invokeLater(new Runnable() 
    {
        public void run() 
        {
            try 
            {
                WindowBuilderTest frame = new WindowBuilderTest();
                frame.setVisible(true);
            } catch (Exception e) 
            {
                e.printStackTrace();
            }
        }
    });
}


// Creating Frame
public WindowBuilderTest() 
{
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 1280, 720 );
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);


    // Create Font
    Font headfont = new Font("Serif", Font.PLAIN, 15);


    // Role Headlines
    final JTextArea txtTop = new JTextArea();
    txtTop.setEditable(false);
    txtTop.setText("TOP");
    txtTop.setBounds(180, 95, 32, 23);
    txtTop.setFont(headfont);
    contentPane.add(txtTop);

    JTextArea txtMid = new JTextArea();
    txtMid.setEditable(false);
    txtMid.setText("MID");
    txtMid.setBounds(252, 95, 32, 23);
    contentPane.add(txtMid);

    JTextArea txtJng = new JTextArea();
    txtJng.setEditable(false);
    txtJng.setText("JNG");
    txtJng.setBounds(320, 95, 32, 23);
    contentPane.add(txtJng);

    JTextArea txtAdc = new JTextArea();
    txtAdc.setEditable(false);
    txtAdc.setText("ADC");
    txtAdc.setBounds(389, 95, 32, 23);
    contentPane.add(txtAdc);

    JTextArea txtSup = new JTextArea();
    txtSup.setEditable(false);
    txtSup.setText("SUP");
    txtSup.setBounds(453, 95, 32, 23);
    contentPane.add(txtSup);

    // Checkbox 1st row
    final JCheckBox t1 = new JCheckBox("");
    t1.setBounds(183, 143, 23, 23);
    t1.addItemListener(new cl());
    contentPane.add(t1);

    JCheckBox m1 = new JCheckBox("");
    m1.setBounds(255, 143, 23, 23);
    contentPane.add(m1);

    JCheckBox j1 = new JCheckBox("");
    j1.setBounds(322, 143, 23, 23);
    contentPane.add(j1);

    JCheckBox a1 = new JCheckBox("");
    a1.setBounds(393, 143, 23, 23);
    contentPane.add(a1);

    JCheckBox s1 = new JCheckBox("");
    s1.setBounds(457, 143, 23, 23);
    contentPane.add(s1);


     class cl implements ItemListener
    {
        @Override
        public void itemStateChanged(ItemEvent e) 
        {
            if(t1.isSelected())
            {
                //Font headfont = txtTop.getFont().deriveFont(Font.BOLD, 40);
                //txtTop.setFont(headfont);
                System.out.println("HURRA!");
            }
            else
            {
                //Font headfont = txtTop.getFont().deriveFont(Font.PLAIN, 40);
                //txtTop.setFont(headfont);
                System.out.println("JUHU!");
            }

        }
    }



}


}

Answer 1

This works for you:

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.border.EmptyBorder;

public class WindowBuilderTest extends JFrame
{

    private JPanel  contentPane;

//Launch the application.
    public static void main(final String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                try
                {
                    final WindowBuilderTest frame = new WindowBuilderTest();
                    frame.setVisible(true);
                }
                catch (final Exception e)
                {
                    e.printStackTrace();
                }
            }
        });
    }

    // Creating Frame
    public WindowBuilderTest()
    {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 1280, 720);
        this.contentPane = new JPanel();
        this.contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(this.contentPane);
        this.contentPane.setLayout(null);

        // Create Font
        final Font headfont = new Font("Serif", Font.PLAIN, 15);

        // Role Headlines
        final JTextArea txtTop = new JTextArea();
        txtTop.setEditable(false);
        txtTop.setText("TOP");
        txtTop.setBounds(180, 95, 32, 23);
        txtTop.setFont(headfont);
        this.contentPane.add(txtTop);

        final JTextArea txtMid = new JTextArea();
        txtMid.setEditable(false);
        txtMid.setText("MID");
        txtMid.setBounds(252, 95, 32, 23);
        this.contentPane.add(txtMid);

        final JTextArea txtJng = new JTextArea();
        txtJng.setEditable(false);
        txtJng.setText("JNG");
        txtJng.setBounds(320, 95, 32, 23);
        this.contentPane.add(txtJng);

        final JTextArea txtAdc = new JTextArea();
        txtAdc.setEditable(false);
        txtAdc.setText("ADC");
        txtAdc.setBounds(389, 95, 32, 23);
        this.contentPane.add(txtAdc);

        final JTextArea txtSup = new JTextArea();
        txtSup.setEditable(false);
        txtSup.setText("SUP");
        txtSup.setBounds(453, 95, 32, 23);
        this.contentPane.add(txtSup);

        // Checkbox 1st row
        addCheckBox(183, 143, 23, 23, txtTop);
        addCheckBox(255, 143, 23, 23, txtMid);
        addCheckBox(322, 143, 23, 23, txtJng);
        addCheckBox(393, 143, 23, 23, txtAdc);
        addCheckBox(457, 143, 23, 23, txtSup);
    }

    private void addCheckBox(final int x, final int y, final int width, final int height, final JTextArea txtTop)
    {
        final JCheckBox checkBox = new JCheckBox();
        checkBox.setBounds(x, y, width, height);
        checkBox.addItemListener(new BoldChanger(txtTop));
        this.contentPane.add(checkBox);
    }

    class BoldChanger implements ItemListener
    {
        private JTextArea   textArea;

        public BoldChanger(final JTextArea textArea)
        {
            this.textArea = textArea;
        }

        @Override
        public void itemStateChanged(final ItemEvent e)
        {
            if (e.getStateChange() == ItemEvent.SELECTED)
            {
                final Font boldFont = this.textArea.getFont().deriveFont(Font.BOLD);
                this.textArea.setForeground(Color.RED);
                this.textArea.setFont(boldFont);
            }
            else
            {
                final Font boldFont = this.textArea.getFont().deriveFont(Font.PLAIN);
                this.textArea.setForeground(Color.BLACK);
                this.textArea.setFont(boldFont);
            }
        }
    }
}

Following problems you had:

• Innerclasses definitions are not allowed inside a method (you had to move it out)
• The final think is true if you work with anynomous classes (those one you define like this ActionListener listner = new ActionListner{ ...} . If you have a class like this, you can access the member variable.

I renamed your ItemListner to BoldChanger . It gets the TextArea to change in the constructor.

Btw:

• CARRY
• JUNGLER ONLY
• TANK
• SUPPORT