Question

import java.awt.Component;
import java.awt.Dimension;
import java.awt.Toolkit;
import javax.swing.JOptionPane;

public class NewJFrame extends javax.swing.JFrame {

    private Component frame;

    public NewJFrame() {
        initComponents();

        //To set the position of the frame window in the center of the screen regardless of the screen resoluiton...
        Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
        int left = (d.width - this.getWidth()) / 2;
        int top = (d.height - this.getHeight()) / 2;
        this.setLocation(left, top);
    }

    private void initComponents() {

        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        jFormattedTextField2 = new javax.swing.JFormattedTextField();
        jButton1 = new javax.swing.JButton();
        jFormattedTextField1 = new javax.swing.JFormattedTextField();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jLabel1.setText("Enter Only Integers");

        jLabel2.setText("Enter Only Alphabets");

        jButton1.setText("Done!");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });

        // SETTING THE COMPONENTS...
        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(35, 35, 35)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(jLabel2)
                            .addComponent(jLabel1))
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(jFormattedTextField1, javax.swing.GroupLayout.DEFAULT_SIZE, 144, Short.MAX_VALUE)
                            .addComponent(jFormattedTextField2, javax.swing.GroupLayout.DEFAULT_SIZE, 144, Short.MAX_VALUE)))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(120, 120, 120)
                        .addComponent(jButton1)))
                .addGap(14, 14, 14))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(29, 29, 29)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel1)
                    .addComponent(jFormattedTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(31, 31, 31)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel2)
                    .addComponent(jFormattedTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 31, Short.MAX_VALUE)
                .addComponent(jButton1)
                .addGap(29, 29, 29))
        );

        pack();
    }

    // NOW HERE GOES THE LOGIC...
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {

        try {
            //Must take only INTEGERS.
            String str1 = jFormattedTextField1.getText();
            int entered_integer = Integer.parseInt(str1);

            //Must take only ALPHABETS.
            String str2 = jFormattedTextField2.getText();

            JOptionPane.showMessageDialog(frame, "Entered Integer is: " + entered_integer + "\nEntered Aplhabet is: " + str2);
            jFormattedTextField1.setText("");
            jFormattedTextField2.setText("");
        } catch (Exception e) {
            JOptionPane.showMessageDialog(frame, "Oops!, You did something wrong!");
            jFormattedTextField1.setText("");
            jFormattedTextField2.setText("");
        }
    }

    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {

            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }

    private javax.swing.JButton jButton1;
    private javax.swing.JFormattedTextField jFormattedTextField1;
    private javax.swing.JFormattedTextField jFormattedTextField2;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;

}

Can anyone tell me why this is used? :

jFormattedTextField.setFormatterFactory(
new DefaultFormatterFactory(new NumberFormatter(new DecimalFormat("#0")))); 

Answer 1

You might look a the InputVerifier example in Validating Input and compare it to the FormattedTextFieldDemo.