如果我们使用可运行的方法SwingUtilities.invokeLater()，而使用文档侦听器应用程序有时会卡住，需要时间更新结果(根据我的实验)。我们也可以使用KeyReleased事件作为文本字段更改监听器，就像这里提到的那样。

usernameTextField.addKeyListener(new KeyAdapter() {
    public void keyReleased(KeyEvent e) {
        JTextField textField = (JTextField) e.getSource();
        String text = textField.getText();
        textField.setText(text.toUpperCase());
    }
});

我知道这涉及到一个非常老的问题，然而，它也给我带来了一些问题。正如kleopatra在上面的评论中回应的那样，我用JFormattedTextField解决了这个问题。然而，解决方案需要更多的工作，但更整洁。

在默认情况下，JFormattedTextField不会在字段中的每个文本更改后触发属性更改。JFormattedTextField的默认构造函数不创建格式化程序。

但是，要执行OP建议的操作，需要使用格式化程序，它将在字段的每次有效编辑之后调用commitEdit()方法。commitEdit()方法触发了我所看到的属性更改，如果没有格式化器，这将在焦点更改或按下enter键时默认触发。

详情见http://docs.oracle.com/javase/tutorial/uiswing/components/formattedtextfield.html#value。

创建一个默认的formatter (DefaultFormatter)对象，通过它的构造函数或setter方法传递给JFormattedTextField。默认格式化器的一个方法是setCommitsOnValidEdit(布尔提交)，它设置格式化器在每次修改文本时触发commitEdit()方法。然后可以使用PropertyChangeListener和propertyChange()方法来获取。

你甚至可以使用“MouseExited”来控制。 例子:

 private void jtSoMauMouseExited(java.awt.event.MouseEvent evt) {                                    
        // TODO add your handling code here:
        try {
            if (Integer.parseInt(jtSoMau.getText()) > 1) {
                //auto update field
                SoMau = Integer.parseInt(jtSoMau.getText());
                int result = SoMau / 5;

                jtSoBlockQuan.setText(String.valueOf(result));
            }
        } catch (Exception e) {

        }

    }   

如果我们使用可运行的方法SwingUtilities.invokeLater()，而使用文档侦听器应用程序有时会卡住，需要时间更新结果(根据我的实验)。我们也可以使用KeyReleased事件作为文本字段更改监听器，就像这里提到的那样。

usernameTextField.addKeyListener(new KeyAdapter() {
    public void keyReleased(KeyEvent e) {
        JTextField textField = (JTextField) e.getSource();
        String text = textField.getText();
        textField.setText(text.toUpperCase());
    }
});

使用KeyListener(在任意键上触发)而不是ActionListener(在进入时触发)

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);
        }
    }