我不明白为什么该代码不起作用（JRadioButtons的新手）

Question

I am learning JRadioButtons and I do not know why it is working in the tutorial I am watching and not in my code. Could someone please take a look at it?

Main Class:

import java.awt.*;
import javax.swing.*;

public class Calculator extends JPanel{
    private static final long serialVersionUID = 1L;

    public static void main(String[] args){
        Screen screen = new Screen();
        screen.setVisible(true);
    }

}

Here is the Screen Class:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JTextArea;

public class Screen extends JFrame implements ActionListener{
    private static final long serialVersionUID = 1L;

    JRadioButton b1, b2;
    ButtonGroup group;
    JTextArea tb;

    public Screen(){
        super("First GUI");
        setSize(600,600);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        JPanel p1 = new JPanel();

        JTextArea tb = new JTextArea("Text Area");

        group = new ButtonGroup();
        group.add(b1);
        group.add(b2);

        b1 = new JRadioButton("Hello");
        b1.setActionCommand("HELLO!");
        b1.addActionListener(this);

        b2 = new JRadioButton("Goodbye");
        b2.setActionCommand("Goodbye! =)");
        b2.addActionListener(this);

        p1.add(b1);
        p1.add(b2);
        p1.add(tb);

        add(p1);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        tb.setText(e.getActionCommand());
    }
}

In my new Java head this should work perfectly. I initialize the buttons, initialize the group. I am getting an error after I click one of the buttons: AWT-EventQueue-0 . I do not know what that means so I do not know how to fix this issue.

Answer 1

You have declared twice the same variable. If you declare the same variable ( JTextArea tb ) in the global and local scope, it will be a separate object. Remove the declaration in the local scope from the Screen() constructor so it will work. Try this

tb = new JTextArea("Text Area");

instead of

JTextArea tb = new JTextArea("Text Area");

Because of your current code, tb is still not initialized in the global scope.