每次更改时自动更新jTextFields的总和（Java）
作为我学习java的一部分，我使用netbeans创建了一个jForm，其中包含三个jTextField，供用户输入一些数字，然后这些numbres的总和显示在另一个jTextField中。 当然，这非常简单，但我希望能够在没有任何按钮的情况下完成此操作。 每当修改3个文本字段中的任何一个时，我都不知道如何“更新”总和。 谁能帮我？
这是我的代码（表单是在设计模式下使用netbeans完成的）：
package sumfields; public class Frame extends javax.swing.JFrame { public Frame() { initComponents(); } @SuppressWarnings("unchecked") // private void initComponents() { n1 = new javax.swing.JTextField(); n2 = new javax.swing.JTextField(); n3 = new javax.swing.JTextField(); sum = new javax.swing.JTextField(); jLabel1 = new javax.swing.JLabel(); jLabel2 = new javax.swing.JLabel(); jLabel3 = new javax.swing.JLabel(); jLabel5 = new javax.swing.JLabel(); jButton1 = new javax.swing.JButton(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); jLabel1.setText("n1"); jLabel2.setText("n2"); jLabel3.setText("n3"); jLabel5.setText("result"); jButton1.setText("Opperate"); jButton1.addActionListener(new java.awt.event.ActionListener() { public void actionPerformed(java.awt.event.ActionEvent evt) { jButton1ActionPerformed(evt); } }); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(15, 15, 15) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING) .addComponent(jLabel1) .addComponent(jLabel2) .addComponent(jLabel3))) .addGroup(layout.createSequentialGroup() .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) .addComponent(jLabel5))) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addComponent(sum, javax.swing.GroupLayout.PREFERRED_SIZE, 59, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(30, 30, 30) .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 79, javax.swing.GroupLayout.PREFERRED_SIZE) .addContainerGap()) .addGroup(layout.createSequentialGroup() .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addComponent(n1, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(n2, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(n3, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE)) .addGap(0, 0, Short.MAX_VALUE)))) ); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(32, 32, 32) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING) .addGroup(layout.createSequentialGroup() .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(n1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(jLabel1)) .addGap(10, 10, 10) .addComponent(n2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) .addComponent(jLabel2)) .addGap(20, 20, 20) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(n3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(jLabel3)) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(sum, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(jButton1) .addComponent(jLabel5)) .addContainerGap(38, Short.MAX_VALUE)) ); pack(); }// private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { int r=Integer.parseInt(n1.getText())+Integer.parseInt(n2.getText())+Integer.parseInt(n3.getText()); sum.setText(""+r); } public static void main(String args[]) { /* Set the Nimbus look and feel */ // /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel. * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html */ try { for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { if ("Nimbus".equals(info.getName())) { javax.swing.UIManager.setLookAndFeel(info.getClassName()); break; } } } catch (ClassNotFoundException ex) { java.util.logging.Logger.getLogger(Frame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (InstantiationException ex) { java.util.logging.Logger.getLogger(Frame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (IllegalAccessException ex) { java.util.logging.Logger.getLogger(Frame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (javax.swing.UnsupportedLookAndFeelException ex) { java.util.logging.Logger.getLogger(Frame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } // /* Create and display the form */ java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new Frame().setVisible(true); } }); } // Variables declaration - do not modify private javax.swing.JButton jButton1; private javax.swing.JLabel jLabel1; private javax.swing.JLabel jLabel2; private javax.swing.JLabel jLabel3; private javax.swing.JLabel jLabel5; private javax.swing.JTextField n1; private javax.swing.JTextField n2; private javax.swing.JTextField n3; private javax.swing.JTextField sum; // End of variables declaration } 正如@Reimeus建议的那样，您需要将Document Listener添加到每个文本字段中。 由于您在jButton1ActionPerformed()方法中执行了添加，因此每当文本字段发生更改时，我都会通知侦听器调用此方法。
注意 ： 根据评论，我更新了我的代码，只包含一个DocumentListener ，并添加了一个DocumentFilter ，只接受数字输入。 我还删除了原始代码中的按钮以执行求和
这是您更新的代码：
import javax.swing.event.DocumentEvent; import javax.swing.event.DocumentListener; import javax.swing.text.AbstractDocument; import javax.swing.text.AttributeSet; import javax.swing.text.BadLocationException; import javax.swing.text.DocumentFilter; public class Frame extends javax.swing.JFrame { public Frame() { initComponents(); } @SuppressWarnings("unchecked") // private void initComponents() { n1 = new javax.swing.JTextField(); n2 = new javax.swing.JTextField(); n3 = new javax.swing.JTextField(); sum = new javax.swing.JTextField(); jLabel1 = new javax.swing.JLabel(); jLabel2 = new javax.swing.JLabel(); jLabel3 = new javax.swing.JLabel(); jLabel5 = new javax.swing.JLabel(); DocumentListener documentListener = new DocumentListener() { @Override public void removeUpdate(DocumentEvent e) { performSummation(null); } @Override public void insertUpdate(DocumentEvent e) { performSummation(null); } @Override public void changedUpdate(DocumentEvent e) { } }; DocumentFilter numericFilter = new DocumentFilter(){ @Override public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException { fb.insertString(offset, string.replaceAll("[^\\d]", ""), attr); } @Override public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException { fb.replace(offset, length, text.replaceAll("[^\\d]", ""), attrs); } }; ((AbstractDocument) n1.getDocument()).setDocumentFilter(numericFilter); ((AbstractDocument) n2.getDocument()).setDocumentFilter(numericFilter); ((AbstractDocument) n3.getDocument()).setDocumentFilter(numericFilter); n1.getDocument().addDocumentListener(documentListener); n2.getDocument().addDocumentListener(documentListener); n3.getDocument().addDocumentListener(documentListener); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); jLabel1.setText("n1"); jLabel2.setText("n2"); jLabel3.setText("n3"); jLabel5.setText("result"); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(15, 15, 15) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING) .addComponent(jLabel1) .addComponent(jLabel2) .addComponent(jLabel3))) .addGroup(layout.createSequentialGroup() .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) .addComponent(jLabel5))) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addComponent(sum, javax.swing.GroupLayout.PREFERRED_SIZE, 59, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(30, 30, 30) .addContainerGap()) .addGroup(layout.createSequentialGroup() .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addComponent(n1, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(n2, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(n3, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE)) .addGap(0, 0, Short.MAX_VALUE)))) ); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(32, 32, 32) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING) .addGroup(layout.createSequentialGroup() .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(n1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(jLabel1)) .addGap(10, 10, 10) .addComponent(n2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) .addComponent(jLabel2)) .addGap(20, 20, 20) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(n3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(jLabel3)) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) .addComponent(sum, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addComponent(jLabel5)) .addContainerGap(38, Short.MAX_VALUE)) ); pack(); }// private void performSummation(java.awt.event.ActionEvent evt) { int total = 0; if(n1.getText().trim().length() > 0){ try{ total += Integer.parseInt(n1.getText()); }catch(NumberFormatException nbx){ } } if(n2.getText().trim().length() > 0){ try{ total += Integer.parseInt(n2.getText()); }catch(NumberFormatException nbx){ } } if(n3.getText().trim().length() > 0){ try{ total += Integer.parseInt(n3.getText()); }catch(NumberFormatException nbx){ } } sum.setText(""+total); } public static void main(String args[]) { /* Set the Nimbus look and feel */ // /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel. * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html */ try { for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { if ("Nimbus".equals(info.getName())) { javax.swing.UIManager.setLookAndFeel(info.getClassName()); break; } } } catch (ClassNotFoundException ex) { java.util.logging.Logger.getLogger(Frame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (InstantiationException ex) { java.util.logging.Logger.getLogger(Frame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (IllegalAccessException ex) { java.util.logging.Logger.getLogger(Frame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (javax.swing.UnsupportedLookAndFeelException ex) { java.util.logging.Logger.getLogger(Frame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } // /* Create and display the form */ java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new Frame().setVisible(true); } }); } // Variables declaration - do not modify private javax.swing.JLabel jLabel1; private javax.swing.JLabel jLabel2; private javax.swing.JLabel jLabel3; private javax.swing.JLabel jLabel5; private javax.swing.JTextField n1; private javax.swing.JTextField n2; private javax.swing.JTextField n3; private javax.swing.JTextField sum; // End of variables declaration }
几个指针：
-
永远不要相信来自用户的输入。 用户可能输入的值不正确（ 比如不是整数 ）。 因此，validation输入并检查输入是否可以实际解析总是一个好主意。 记住这一点，我更新了你的
jButton1ActionPerformed()方法 -
另一种方法是使用格式化文本字段
您正在寻找的是DocumentListener 。
为每个JTextFields n1 ， n2和n3注册一个监听器，并调用方法jButton1ActionPerformed来更新结果字段。
此替代方法使用PropertyChangeListener和FocusListener使用JFormattedTextField update()一个值的总和。
您可以使用焦点侦听器，也可以对输入JTextField使用动作侦听器