JPanel 占据了整个 JFrame

Question

我有一个问题，当我在 JFrame 中包含 JPanel 时，它会覆盖整个屏幕。我的代码是

import java.awt.*;

import javax.swing.*;

public class TestFrameExample extends JPanel {

    static String TheQuestion;
    static String QN1 = "Question 1: ";

    static String Q1 = "What is Lead's chemical symbol?";

    static String brk = "___________________";

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        this.setBackground(new Color(135, 206, 250));

        g.setFont(new Font("Tahoma", Font.BOLD, 48));
        g.setColor(Color.WHITE);
        g.drawString(QN1, 80, 100);

        g.setFont(new Font("Tahoma", Font.BOLD, 48));
        g.setColor(Color.WHITE);
        g.drawString(brk, 60, 130);

        g.setFont(new Font("Tahoma", Font.PLAIN, 36));
        g.setColor(Color.WHITE);
        g.drawString(Q1, 80, 200);
    }



    public static void main(String[] args) {

        TestFrameExample graphics = new TestFrameExample();
        JFrame ThisFrame = new JFrame();

        TheQuestion = QN1;

        JTextField txt = new JTextField(10);
        JPanel Panel = new JPanel();

        ThisFrame.setTitle("Question 1");
        ThisFrame.setSize(720, 480);
        ThisFrame.setLocationRelativeTo(null);
        ThisFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        ThisFrame.setVisible(true);
        ThisFrame.add(graphics);

        Panel.setBackground(new Color(135, 206, 250));
        Panel.setSize(null);
        Panel.setLocation(null);
        Panel.add(txt);
        ThisFrame.add(Panel);

    }
}

但是，当我改变时

Panel.setLocation(null)

到

Panel.setLocation(80, 250)

它覆盖了整个屏幕。

有人可以帮我把它放在屏幕上的正确位置吗？

更新

我按照我在评论中所说的进行了修改，并阅读了代码

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

public class TestFrameExample extends JPanel {

static String TheQuestion;
static String QN1 = "Question 1: ";

static String Q1 = "What is Lead's chemical symbol?";

static String brk = "___________________";

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    this.setBackground(new Color(135, 206, 250));

    g.setFont(new Font("Tahoma", Font.BOLD, 48));
    g.setColor(Color.WHITE);
    g.drawString(QN1, 80, 100);

    g.setFont(new Font("Tahoma", Font.BOLD, 48));
    g.setColor(Color.WHITE);
    g.drawString(brk, 60, 130);

    g.setFont(new Font("Tahoma", Font.PLAIN, 36));
    g.setColor(Color.WHITE);
    g.drawString(Q1, 80, 200);
}



public static void main(String[] args) {

    TestFrameExample graphics = new TestFrameExample();
    JFrame ThisFrame = new JFrame();

    TheQuestion = QN1;

    JTextField txt = new JTextField(20);
    JPanel panel = new JPanel();

    ThisFrame.setTitle("Question 1");
    ThisFrame.setSize(720, 480);
    ThisFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ThisFrame.add(graphics);

    panel.setBackground(new Color(135, 206, 250));
    panel.add(txt);
    ThisFrame.add(panel);
    ThisFrame.add(panel, BorderLayout.PAGE_END);

    ThisFrame.setLocationRelativeTo(null);
    ThisFrame.setVisible(true);

}
}

它将输入文本放在屏幕底部，但屏幕的其余部分保持灰色。

但是我根本不明白您发布的第二组代码；这远远超出了我的技能范围（过去 6 周我才学习 Java）。在这个阶段我所寻找的只是使面板不会使屏幕的其余部分变黑。

是否可以仅通过修改当前代码集来实现，还是我必须完全重写代码？

Answer 1

JFrame 的 contentPane 默认使用 BorderLayout，您可以利用它来发挥自己的优势：

• 将您的 TestFrameExample 对象 BorderLayout.CENTER 添加到您的 JFrame
• 在BorderLayout.PAGE_END 位置将您的其他JPanel，或者只是一个JTextField 添加到JFrame。这会将组件添加到 GUI 的底部。
• 不要在您的组件上调用 setLocation(...)，因为这会导致使用 null 布局，这种布局会导致难以调试和升级的僵化 GUI。

有关更多详细信息，请阅读教程中的 BorderLayout。

例如，

public static void main(String[] args) {
    TestFrameExample graphics = new TestFrameExample();
    JFrame thisFrame = new JFrame();

    TheQuestion = QN1;

    JTextField txt = new JTextField(10);
    JPanel panel = new JPanel();

    thisFrame.setTitle("Question 1");
    thisFrame.setSize(720, 480); // better to not do this, but to pack instead
    // thisFrame.setLocationRelativeTo(null);
    thisFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    // thisFrame.setVisible(true); // *** not yet ***
    thisFrame.add(graphics, BorderLayout.CENTER);

    panel.setBackground(new Color(135, 206, 250));
    // panel.setSize(null); // *** don't do this ***
    // panel.setLocation(null); // *** don't do this ***
    panel.add(txt);
    thisFrame.add(panel, BorderLayout.PAGE_END);

    thisFrame.setLocationRelativeTo(null);
    thisFrame.setVisible(true); // *** HERE ***

}

---

请注意，如果可能的话，我会避免直接绘制，而是使用组件和布局管理器。这应该更容易显示不同类型的问题。例如，运行以下程序并反复按<enter> 键，滚动问题以了解我的意思：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;

import javax.swing.*;

public class TestQuestion2 extends JPanel {
   private static final Color BACKGROUND = new Color(135, 206, 250);
   private static final Color LABEL_FOREGROUND = Color.white;
   private static final int EB_GAP = 60;
   private static final int PREF_W = 720;
   private static final int PREF_H = 480;
   private static final Font TITLE_FONT = new Font("Tahoma", Font.BOLD, 48);
   private static final Font Q_FONT = TITLE_FONT.deriveFont(Font.PLAIN, 36f);
   private JLabel questionTitleLabel = new JLabel();
   private JTextArea questionArea = new JTextArea(4, 10);
   private JTextField answerField = new JTextField(20);
   private Question question;
   private List<Question> questionList;
   private int questionListIndex = 0;

   public TestQuestion2(List<Question> questionList) {
      this.questionList = questionList;
      questionTitleLabel.setFont(TITLE_FONT);
      questionTitleLabel.setForeground(LABEL_FOREGROUND);
      JSeparator separator = new JSeparator();
      separator.setForeground(LABEL_FOREGROUND);

      questionArea.setFont(Q_FONT);
      questionArea.setForeground(LABEL_FOREGROUND);
      questionArea.setWrapStyleWord(true);
      questionArea.setLineWrap(true);
      questionArea.setBorder(null);
      questionArea.setOpaque(false);
      questionArea.setFocusable(false);
      JScrollPane scrollPane = new JScrollPane(questionArea);
      scrollPane.setBorder(null);
      scrollPane.setOpaque(false);
      scrollPane.getViewport().setOpaque(false);

      JPanel answerPanel = new JPanel();
      answerPanel.add(answerField);
      answerPanel.setOpaque(false);

      setBackground(BACKGROUND);
      setBorder(BorderFactory.createEmptyBorder(EB_GAP, EB_GAP, EB_GAP, EB_GAP));
      setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
      add(questionTitleLabel);
      add(Box.createHorizontalStrut(10));
      add(separator);
      add(Box.createHorizontalStrut(5));
      add(scrollPane);
      add(Box.createHorizontalGlue());
      add(answerPanel);

      setQuestion(questionList.get(questionListIndex));

      answerField.addActionListener(new AnswerListener());
   }

   public void setQuestion(Question question) {
      this.question = question;
      questionTitleLabel.setText("Question " + question.getNumber() + ":");
      questionArea.setText(question.getQuestion());
   }

   @Override
   public Dimension getPreferredSize() {
      Dimension superSz = super.getPreferredSize();
      if (isPreferredSizeSet()) {
         return superSz;
      }
      int prefW = Math.max(superSz.width, PREF_W);
      int prefH = Math.max(superSz.height, PREF_H);
      return new Dimension(prefW, prefH);
   }

   private class AnswerListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent e) {
         questionListIndex++;
         questionListIndex %= questionList.size();
         setQuestion(questionList.get(questionListIndex));
      }
   }

   private static void createAndShowGui() {
      List<Question> questionList = new ArrayList<>();
      questionList.add(new Question(1, "What is Lead's chemical symbol?"));
      questionList.add(new Question(2, "Who is buried in Grant's tomb?"));
      questionList.add(new Question(3, "What ..... is your quest?"));
      questionList.add(new Question(4, "What ..... is your favorite color?"));
      questionList.add(new Question(5, "What is the capital of Assyria?"));
      questionList.add(new Question(6, "What is the airspeed velocity of the unladen laden swallow?"));
      questionList.add(new Question(7, "This will be a very long question, one that shows the display "
            + "of multiple lines, and a JTextArea that looks like a JLabel. "
            + "What do you think of it?"));

      TestQuestion2 testQuestion2Panel = new TestQuestion2(questionList);

      JFrame frame = new JFrame("Question");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(testQuestion2Panel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

class Question {
   private int number;
   private String question;
   private List<String> possibleAnswers;

   public Question(int number, String question) {
      this.number = number;
      this.question = question;
   }
   public int getNumber() {
      return number;
   }
   public void setNumber(int number) {
      this.number = number;
   }
   public String getQuestion() {
      return question;
   }
   public void setQuestion(String question) {
      this.question = question;
   }
}