Java JTextField或JLabel未更新的JPanel

我曾试图找到答案，但我没有找到答案。我对java相当陌生。我有4个类（1个带有JFrame的main和3个JPanel）。 main类创建JFrame并向其中添加3个面板。 我试图完成的是从另一个面板（panelB）中的ActionEvent更新一个面板（panelA）中的JLabel或JTextField。 panelB中的ActionEvent在panelA中运行一个方法，该方法运行setText（）方法和repaint（）方法。我无法使用新文本更新JLabel或JTextField

这是我的代码：

App.java BottomPanel.java MiddlePanel.java

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感谢您的帮助。

在OKButtonListener中，您创建了一个新的BottomPanel实例，该实例与您添加到JFrame中的BottomPanel无关。

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您将需要在JFrame中添加的底部面板的实际引用。

d1rk将其锁定。这里有一种实现这种效果的方法

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.event.*;
import javax.swing.*;

public class App {
    public static void main(String[] args) {
        JFrame nameFrame = new JFrame("Name Form");
        nameFrame.setLayout(new BorderLayout());
        nameFrame.setSize(300,150);
        nameFrame.setLocationRelativeTo(null);
        nameFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        BottomPanel bottomPanel = new BottomPanel();

        MiddlePanel middlePanel = new MiddlePanel(bottomPanel);
        nameFrame.add(middlePanel, BorderLayout.CENTER);
        nameFrame.add(bottomPanel, BorderLayout.SOUTH);
        nameFrame.setVisible(true);
    }
}

class BottomPanel extends JPanel {
    private JLabel welcomeLabel = new JLabel("Old Text");

    BottomPanel() {
        super(new FlowLayout());
        add(welcomeLabel);
    }
    public void setText(String text) {
        welcomeLabel.setText(text);
        repaint();
    }
}

class MiddlePanel extends JPanel {

    private BottomPanel bottomPanel;

    MiddlePanel(BottomPanel bottomPanel) {
        super(new BorderLayout());

        this.bottomPanel = bottomPanel;

        JButton okButton = new JButton("OK");
        okButton.setSize(20, 20);
        OKButtonListener okButtonListener = new OKButtonListener();
        okButton.addActionListener(okButtonListener);

        add(okButton, BorderLayout.EAST);
    }
    class OKButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //BottomPanel bottomPanel = new BottomPanel();
            bottomPanel.setText("New Text");
        }
    }
}

顺便说一下-

ok按钮。设置大小（20,20）不要这样做。布局管理器将忽略它，如果不忽略它，它将是脆弱的。
import java.awt.FlowLayout;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class BottomPanel extends JPanel {
    private JLabel welcomeLabel = new JLabel("Old Text");

    BottomPanel() {
        super(new FlowLayout());
        add(welcomeLabel);
    }
    public void setText(String text) {
        welcomeLabel.setText(text);
        repaint();
    }
}

import java.awt.BorderLayout;
import javax.swing.JButton;
import javax.swing.JTextArea;
import javax.swing.JPanel;
import java.awt.event.*;
import java.awt.Graphics;

public class MiddlePanel extends JPanel {
    MiddlePanel() {
        super(new BorderLayout());

        JButton okButton = new JButton("OK");
        okButton.setSize(20, 20);
        OKButtonListener okButtonListener = new OKButtonListener();
        okButton.addActionListener(okButtonListener);

        add(okButton, BorderLayout.EAST);
    }
    class OKButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            BottomPanel bottomPanel = new BottomPanel();
            bottomPanel.setText("New Text");
        }
    }
}

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.event.*;
import javax.swing.*;

public class App {
    public static void main(String[] args) {
        JFrame nameFrame = new JFrame("Name Form");
        nameFrame.setLayout(new BorderLayout());
        nameFrame.setSize(300,150);
        nameFrame.setLocationRelativeTo(null);
        nameFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        BottomPanel bottomPanel = new BottomPanel();

        MiddlePanel middlePanel = new MiddlePanel(bottomPanel);
        nameFrame.add(middlePanel, BorderLayout.CENTER);
        nameFrame.add(bottomPanel, BorderLayout.SOUTH);
        nameFrame.setVisible(true);
    }
}

class BottomPanel extends JPanel {
    private JLabel welcomeLabel = new JLabel("Old Text");

    BottomPanel() {
        super(new FlowLayout());
        add(welcomeLabel);
    }
    public void setText(String text) {
        welcomeLabel.setText(text);
        repaint();
    }
}

class MiddlePanel extends JPanel {

    private BottomPanel bottomPanel;

    MiddlePanel(BottomPanel bottomPanel) {
        super(new BorderLayout());

        this.bottomPanel = bottomPanel;

        JButton okButton = new JButton("OK");
        okButton.setSize(20, 20);
        OKButtonListener okButtonListener = new OKButtonListener();
        okButton.addActionListener(okButtonListener);

        add(okButton, BorderLayout.EAST);
    }
    class OKButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //BottomPanel bottomPanel = new BottomPanel();
            bottomPanel.setText("New Text");
        }
    }
}