将矢量打印到 JTextArea 时出现间距错误

Question

所以我正在努力构建一个基于 Java Swing GUI 的数据库系统...我有一个按钮可以将人/事物添加到向量（在本例中为数据库）：

// Database
Vector<String> db = new Vector<String>();

这是要添加的按钮的动作监听器：

new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        String newStudent = student.getText();
        db.addElement(newStudent);

这部分似乎一切正常，但是，当我使用字符串缓冲区打印出 JTextArea 上的矢量时，JTextArea 上的文本中存在奇怪的间距问题

这是我将向量打印到 JTextArea 上的 StringBuffer 和部分：

StringBuffer dbb = new StringBuffer();
for (int i = 0; i < db.size(); i++) {
    dbb.append(db.get(i) + '\n');
}
// printDB is the JTextArea
printDB.setText(dbb.toString());
    add(printDB);

间距问题的屏幕截图： Screenshot

关于可能导致此问题的任何想法？间距似乎也是线性的（1space，2spaces，3spaces...）

• 如果需要，可以链接到完整的项目（抱歉，一般来说代码不好，哈哈，我才刚刚开始）：Full Code

• 抱歉，如果线性不是正确的词，顺便说一句，我想不出另一种方式来描述它

代码：

import java.awt.*;
import java.awt.event.*;
import java.io.IOException;
import java.util.*;
import java.util.Vector.*;
import javax.swing.*;

public class Database extends JFrame implements ActionListener, EventListener {

   // Database
   Vector<String> db = new Vector<String>();

   // Main Menu Buttons:
   JButton addStudent = new JButton("Add Student");
   JButton deleteStudent = new JButton("Delete Button");
   JButton deleteAll = new JButton("Delete All Students");
   JButton printAll = new JButton("Print Database");
   JTextArea welcome = new JTextArea("Welcome!");

   // Add Student Menu:
   JTextField student = new JTextField();
   JButton submit = new JButton("Add Student");

   // Print Students
   JTextArea printDB = new JTextArea();
   JButton returnMenu = new JButton("Return to Menu");

   public Database() {
      super("DatabaseGUI");
      setSize(800, 600);

      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setLayout(null);
      setResizable(false);
      welcome.setBackground(this.getForeground());
      add(welcome);
      welcome.setSize(60, 15);
      welcome.setLocation(386, 300);
      add(addStudent);
      addStudent.setSize(150, 50);
      addStudent.setLocation(25, 100);
      add(deleteStudent);
      deleteStudent.setSize(150, 50);
      deleteStudent.setLocation(625, 100);
      add(deleteAll);
      deleteAll.setLocation(225, 100);
      deleteAll.setSize(150, 50);
      add(printAll);
      printAll.setLocation(425, 100);
      printAll.setSize(150, 50);
      addStudent.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            welcome.setVisible(false);
            addStudent.setVisible(false);
            deleteStudent.setVisible(false);
            deleteAll.setVisible(false);
            printAll.setVisible(false);
            add(student);
            add(submit);
            submit.setVisible(true);
            submit.setSize(150, 30);
            submit.setLocation(425, 250);
            student.setVisible(true);
            student.setSize(150, 30);
            student.setLocation(275, 250);
            submit.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                  String newStudent = student.getText();
                  db.addElement(newStudent);
                  student.setText(null);
                  student.setVisible(false);
                  submit.setVisible(false);
                  welcome.setVisible(true);
                  addStudent.setVisible(true);
                  deleteStudent.setVisible(true);
                  deleteAll.setVisible(true);
                  printAll.setVisible(true);
               }
            });
         }
      });
      printAll.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            welcome.setVisible(false);
            addStudent.setVisible(false);
            deleteStudent.setVisible(false);
            deleteAll.setVisible(false);
            printAll.setVisible(false);
            StringBuffer dbb = new StringBuffer();
            for (int i = 0; i < db.size(); i++) {
               dbb.append(db.get(i) + '\n');
            }
            printDB.setText(dbb.toString());
            add(printDB);
            printDB.setSize(300, 400);
            printDB.setEditable(false);
            printDB.setLocation(100, 100);
            printDB.setVisible(true);
            add(returnMenu);
            returnMenu.setVisible(true);
            returnMenu.setSize(200, 30);
            returnMenu.setLocation(500, 400);
            returnMenu.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                  returnMenu.setVisible(false);
                  printDB.setVisible(false);
                  welcome.setVisible(true);
                  addStudent.setVisible(true);
                  deleteStudent.setVisible(true);
                  deleteAll.setVisible(true);
                  printAll.setVisible(true);
               }
            });
         }
      });
      setVisible(true);
   }

   public static void main(String[] args) {
      Database student = new Database();
   }

   @Override
   public void actionPerformed(ActionEvent e) {
      // TODO Auto-generated method stub

   }

}

Answer 1

您在 addStudent ActionListener 中反复向提交按钮添加一个 ActionListener，这意味着当按下 addStudent 时，将添加越来越多的 ActionListener 来提交，这不是您想要的。

建议：

• 只向您的 JButtons 添加一个 ActionListener，而不是在可能被多次调用的其他事件侦听器中。考虑在类构造函数中添加所有 ActionListener。

边记录：

• 不要使用绝对定位和空布局。虽然空布局和setBounds() 对于 Swing 新手来说似乎是创建复杂 GUI 的最简单和最好的方法，但创建的 Swing GUI 越多，使用它们时遇到的困难就越严重。当 GUI 调整大小时，它们不会调整您的组件大小，它们是增强或维护的皇家女巫，放置在滚动窗格中时它们完全失败，在与原始不同的所有平台或屏幕分辨率上查看时它们看起来很糟糕.
• 了解如何使用 CardLayout，然后使用 CardLayout 让您干净轻松地交换视图。

---

例如，

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;

@SuppressWarnings("serial")
public class Database2 extends JPanel {
   // constants for the cards
   public static final String WELCOME = "welcome";
   public static final String ADD_STUDENT = "add student";
   public static final String DISPLAY_DATA = "display data";

   private JTextArea displayTextArea = new JTextArea(15, 20);
   private JTextField addStudentField = new JTextField(10);
   private CardLayout cardLayout = new CardLayout();
   private List<String> db = new ArrayList<>();

   public Database2() {
      // prepare JTextArea
      displayTextArea.setWrapStyleWord(true);
      displayTextArea.setLineWrap(true);
      displayTextArea.setFocusable(false);

      // set layout as CardLayout and add all JPanels with constants
      setLayout(cardLayout);
      add(createWelcomePanel(), WELCOME);
      add(createAddStudentPanel(), ADD_STUDENT);
      add(createDisplayDataPanel(), DISPLAY_DATA);
   }

   private JPanel createWelcomePanel() {
      ShowStudentPanelAction showStudentAction = new ShowStudentPanelAction("Add Student");
      DisplayDataAction displayDataAction = new DisplayDataAction("Display Data");
      JButton addStudentButton = new JButton(showStudentAction);
      JButton displayDataButton = new JButton(displayDataAction);

      JPanel topPanel = new JPanel(new GridLayout(1, 0, 5, 0));
      topPanel.add(addStudentButton);
      topPanel.add(displayDataButton);
      topPanel.add(new JButton(new ExitAction("Exit", KeyEvent.VK_X)));

      JLabel welcomeLabel = new JLabel("Welcome", SwingConstants.CENTER);
      // make JLabel text bigger
      welcomeLabel.setFont(welcomeLabel.getFont().deriveFont(Font.BOLD, 42f));

      // and give it a border 30 points wide
      int ebGap = 30;
      welcomeLabel.setBorder(BorderFactory.createEmptyBorder(ebGap, ebGap,
            ebGap, ebGap));

      JPanel welcomePanel = new JPanel(new BorderLayout());
      ebGap = 4;
      welcomePanel.setBorder(BorderFactory.createEmptyBorder(ebGap, ebGap, ebGap, ebGap));
      welcomePanel.add(topPanel, BorderLayout.PAGE_START);
      welcomePanel.add(welcomeLabel, BorderLayout.CENTER);

      return welcomePanel;
   }

   private JPanel createAddStudentPanel() {
      AddStudentAction addStudentAction = new AddStudentAction("Add Student");
      addStudentField.setAction(addStudentAction);
      JPanel addStudentPanel = new JPanel();
      addStudentPanel.add(addStudentField);
      addStudentPanel.add(new JButton(addStudentAction)); 
      return addStudentPanel;
   }

   private JPanel createDisplayDataPanel() {
      JPanel displayDataPanel = new JPanel();
      JScrollPane scrollPane = new JScrollPane(displayTextArea);
      scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
      displayDataPanel.add(scrollPane);
      displayDataPanel.add(new JButton(new ReturnToWelcomeAction("Return")));
      return displayDataPanel;
   }

   private class ShowStudentPanelAction extends AbstractAction {
      public ShowStudentPanelAction(String name) {
         super(name);
         int mnemonic = (int) name.charAt(0);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         cardLayout.show(Database2.this, ADD_STUDENT);
         addStudentField.requestFocusInWindow();
         addStudentField.selectAll();
      }
   }

   private class DisplayDataAction extends AbstractAction {
      public DisplayDataAction(String name) {
         super(name);
         int mnemonic = (int) name.charAt(0);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         StringBuilder sb = new StringBuilder();
         for (String studentName : db) {
            sb.append(studentName + "\n");
         }
         displayTextArea.setText(sb.toString());
         cardLayout.show(Database2.this, DISPLAY_DATA);
      }
   }

   private class AddStudentAction extends AbstractAction {
      public AddStudentAction(String name) {
         super(name);
         int mnemonic = (int) name.charAt(0);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         String studentText = addStudentField.getText();
         db.add(studentText);
         cardLayout.show(Database2.this, WELCOME);
      }
   }

   private class ReturnToWelcomeAction extends AbstractAction {
      public ReturnToWelcomeAction(String name) {
         super(name);
         int mnemonic = (int) name.charAt(0);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         cardLayout.show(Database2.this, WELCOME);
      }
   }

   private class ExitAction extends AbstractAction {
      public ExitAction(String name, int mnemonic) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         Window window = SwingUtilities.getWindowAncestor(Database2.this);
         if (window != null) {
            window.dispose();
         }
      }
   }

   private static void createAndShowGui() {
      Database2 mainPanel = new Database2();

      JFrame frame = new JFrame("Database2");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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