java - 我想要做到这一点，所以如果我点击 btnNewButton 它会更改 textArea 上的文本

Question

我尝试过textArea.setText();但这行不通。我真的不知道还能做什么。我知道可能有一些简单的方法可以做到这一点，但我很困惑。请帮忙。我知道java。但 Swing 让我感到困惑。

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import java.awt.GridLayout;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import javax.swing.JTextField;
import javax.swing.JTextArea;
import javax.swing.JButton;
import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;


public class GeoUI extends JFrame{


    private static final long serialVersionUID = 1L;
    private JPanel contentPane;
    private JTextField textField;
    private JTextField textField_1;
    final JTextArea textArea = new JTextArea();
    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    GeoUI frame = new GeoUI();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public GeoUI() {
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 150);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(new GridLayout(0, 3, 0, 0));

        JPanel panel = new JPanel();
        contentPane.add(panel);
        panel.setLayout(new GridLayout(3, 1, 0, 0));

        JLabel lblRadiussidelength = new JLabel("Radius/SideLength:");
        lblRadiussidelength.setHorizontalAlignment(SwingConstants.CENTER);
        panel.add(lblRadiussidelength);

        JLabel lblShape = new JLabel("Shape:");
        lblShape.setHorizontalAlignment(SwingConstants.CENTER);
        panel.add(lblShape);

        JPanel panel_1 = new JPanel();
        contentPane.add(panel_1);
        panel_1.setLayout(new GridLayout(3, 1, 0, 0));

        textField_1 = new JTextField();
        panel_1.add(textField_1);
        textField_1.setColumns(10);

        textField = new JTextField();
        panel_1.add(textField);
        textField.setColumns(10);



        JButton btnNewButton = new JButton("Go");
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                textArea.setText("slflkdsjfskl");

            }


        });
        panel_1.add(btnNewButton);

        JPanel panel_2 = new JPanel();
        contentPane.add(panel_2);
        panel_2.setLayout(new GridLayout(1, 0, 0, 0));

        JTextArea textArea = new JTextArea();
        textArea.setEditable(false);
        panel_2.add(textArea);
    }
}

Answer 1

当 ActionListener 注册到按钮时，

textArea 尚未定义。在注册监听器之前，先声明(作为 final)并初始化组件。

final JTextArea textArea = new JTextArea();