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Updating the sum of jTextFields automatically everytime they change (Java)

由 ￣綄美尐妖づ 提交于 2019-11-28 13:49:15

As @Reimeus suggested, you need to add Document Listener to each of your text fields. Since you're performing the addition in your jButton1ActionPerformed() method, I made the notification of the listeners call this method whenever there's a change to your text fields.

Note: Based on the comments, I've updated my code to include only one DocumentListener and also added a DocumentFilter to accept only numeric input. I also removed the button that was present in the original code to perform the summation

Here's your updated code:

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")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    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();
    }// </editor-fold>

    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 */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* 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);
        }
        //</editor-fold>

        /* 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
}

A couple of pointers:

  • Never trust the input that comes from the user. There's a possibility that the user might enter an incorrect value (say something that is not an Integer). As such it is always a good idea to validate your input and check whether the input can be actually parsed. Keeping this in mind, I'ved updated your jButton1ActionPerformed() method

  • The other alternative is to use a Formatted Text Fields

What you are looking for is a DocumentListener.

Register a listener with each of your JTextFields n1, n2 and n3 and call your method jButton1ActionPerformed to update the result field.

trashgod

This alternative approach uses a PropertyChangeListener and a FocusListener to update() a sum of values using JFormattedTextField.

You can use a focus listener or you can use a action listener to the input JTextField

标签
java
swing
jtextcomponent
documentlistener
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