一种优雅的方法是将侦听器添加到插入符号位置，因为每次键入/删除内容时它都会更改，然后只需将旧值与当前值进行比较。

String oldVal = ""; // empty string or default value
JTextField tf = new JTextField(oldVal);

tf.addCaretListener(e -> {
    String currentVal = tf.getText();

    if(!currentVal.equals(oldVal)) {
        oldVal = currentVal;
        System.out.println("Change"); // do something
    }
});

(此事件也被触发每次用户只是点击进入TextField)。

Be aware that when the user modify the field, the DocumentListener can, sometime, receive two events. For instance if the user selects the whole field content, then press a key, you'll receive a removeUpdate (all the content is remove) and an insertUpdate. In your case, I don't think it is a problem but, generally speaking, it is. Unfortunately, it seems there's no way to track the content of the textField without subclassing JTextField. Here is the code of a class that provide a "text" property :

package net.yapbam.gui.widget;

import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;

/** A JTextField with a property that maps its text.
 * <br>I've found no way to track efficiently the modifications of the text of a JTextField ... so I developed this widget.
 * <br>DocumentListeners are intended to do it, unfortunately, when a text is replace in a field, the listener receive two events:<ol>
 * <li>One when the replaced text is removed.</li>
 * <li>One when the replacing text is inserted</li>
 * </ul>
 * The first event is ... simply absolutely misleading, it corresponds to a value that the text never had.
 * <br>Anoter problem with DocumentListener is that you can't modify the text into it (it throws IllegalStateException).
 * <br><br>Another way was to use KeyListeners ... but some key events are throw a long time (probably the key auto-repeat interval)
 * after the key was released. And others events (for example a click on an OK button) may occurs before the listener is informed of the change.
 * <br><br>This widget guarantees that no "ghost" property change is thrown !
 * @author Jean-Marc Astesana
 * <BR>License : GPL v3
 */

public class CoolJTextField extends JTextField {
    private static final long serialVersionUID = 1L;

    public static final String TEXT_PROPERTY = "text";

    public CoolJTextField() {
        this(0);
    }

    public CoolJTextField(int nbColumns) {
        super("", nbColumns);
        this.setDocument(new MyDocument());
    }

    @SuppressWarnings("serial")
    private class MyDocument extends PlainDocument {
        private boolean ignoreEvents = false;

        @Override
        public void replace(int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
            String oldValue = CoolJTextField.this.getText();
            this.ignoreEvents = true;
            super.replace(offset, length, text, attrs);
            this.ignoreEvents = false;
            String newValue = CoolJTextField.this.getText();
            if (!oldValue.equals(newValue)) CoolJTextField.this.firePropertyChange(TEXT_PROPERTY, oldValue, newValue);
        }

        @Override
        public void remove(int offs, int len) throws BadLocationException {
            String oldValue = CoolJTextField.this.getText();
            super.remove(offs, len);
            String newValue = CoolJTextField.this.getText();
            if (!ignoreEvents && !oldValue.equals(newValue)) CoolJTextField.this.firePropertyChange(TEXT_PROPERTY, oldValue, newValue);
        }
    }

向底层Document中添加侦听器，底层Document是自动为您创建的。

// Listen for changes in the text
textField.getDocument().addDocumentListener(new DocumentListener() {
  public void changedUpdate(DocumentEvent e) {
    warn();
  }
  public void removeUpdate(DocumentEvent e) {
    warn();
  }
  public void insertUpdate(DocumentEvent e) {
    warn();
  }

  public void warn() {
     if (Integer.parseInt(textField.getText())<=0){
       JOptionPane.showMessageDialog(null,
          "Error: Please enter number bigger than 0", "Error Message",
          JOptionPane.ERROR_MESSAGE);
     }
  }
});

只需创建一个扩展DocumentListener并实现所有DocumentListener方法的接口:

@FunctionalInterface
public interface SimpleDocumentListener extends DocumentListener {
    void update(DocumentEvent e);

    @Override
    default void insertUpdate(DocumentEvent e) {
        update(e);
    }
    @Override
    default void removeUpdate(DocumentEvent e) {
        update(e);
    }
    @Override
    default void changedUpdate(DocumentEvent e) {
        update(e);
    }
}

然后:

jTextField.getDocument().addDocumentListener(new SimpleDocumentListener() {
    @Override
    public void update(DocumentEvent e) {
        // Your code here
    }
});

或者你甚至可以使用lambda表达式:

jTextField.getDocument().addDocumentListener((SimpleDocumentListener) e -> {
    // Your code here
});

textBoxName.getDocument().addDocumentListener(new DocumentListener() {
   @Override
   public void insertUpdate(DocumentEvent e) {
       onChange();
   }

   @Override
   public void removeUpdate(DocumentEvent e) {
      onChange();
   }

   @Override
   public void changedUpdate(DocumentEvent e) {
      onChange();
   } 
});

但我不会仅仅将用户(可能是意外)在键盘上触碰的任何东西解析为Integer。你应该捕获抛出的任何异常，并确保JTextField不是空的。

我对WindowBuilder是全新的，事实上，几年之后才回到Java，但我实现了“一些东西”，然后我想我应该查一下，遇到了这个线程。

我正在测试这个，所以，基于对这一切的新手，我确信我一定遗漏了一些东西。

下面是我所做的，其中“runTxt”是一个文本框，“runName”是类的数据成员:

public void focusGained(FocusEvent e) {
    if (e.getSource() == runTxt) {
        System.out.println("runTxt got focus");
        runTxt.selectAll();
    }
}

public void focusLost(FocusEvent e) {
    if (e.getSource() == runTxt) {
        System.out.println("runTxt lost focus");
        if(!runTxt.getText().equals(runName))runName= runTxt.getText();
        System.out.println("runText.getText()= " + runTxt.getText() + "; runName= " + runName);
    }
}

似乎比这里到目前为止简单得多，而且似乎是有效的，但是，因为我正在写这篇文章，我很高兴听到任何被忽视的陷阱。这是一个问题，用户可以进入和离开文本框w/o作出改变?我认为你所做的一切都是不必要的任务。