Question

write a complete java class that contains only one jtextfield .write only needed code to allow user to input octal number inside this jtextfield .also need to change the jtextfield's foreground color to red when an invalid digit is entered

Answer 1

public class NewJFrame extends javax.swing.JFrame {

public NewJFrame() {
initComponents();
}

@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">//GEN-BEGIN:initComponents
private void initComponents() {

panel = new javax.swing.JPanel();
textField = new javax.swing.JTextField();

setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

panel.setBackground(new java.awt.Color(204, 255, 204));

textField.setFont(new java.awt.Font("Times New Roman", 0, 18)); // NOI18N
textField.addKeyListener(new java.awt.event.KeyAdapter() {
public void keyReleased(java.awt.event.KeyEvent evt) {
textFieldKeyReleased(evt);
}
});

javax.swing.GroupLayout panelLayout = new javax.swing.GroupLayout(panel);
panel.setLayout(panelLayout);
panelLayout.setHorizontalGroup(
panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(panelLayout.createSequentialGroup()
.addContainerGap()
.addComponent(textField, javax.swing.GroupLayout.DEFAULT_SIZE, 439, Short.MAX_VALUE)
.addContainerGap())
);
panelLayout.setVerticalGroup(
panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(panelLayout.createSequentialGroup()
.addGap(122, 122, 122)
.addComponent(textField, javax.swing.GroupLayout.PREFERRED_SIZE, 42, javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap(136, Short.MAX_VALUE))
);

javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(panel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(panel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);

pack();
}// </editor-fold>//GEN-END:initComponents

private void textFieldKeyReleased(java.awt.event.KeyEvent evt) {//GEN-FIRST:event_textFieldKeyReleased
char[] charArray = textField.getText().toCharArray();
boolean detect = true;
for (char ch : charArray) {
switch (ch) {
case '0': break;
case '1': break;
case '2': break;
case '3': break;
case '4': break;
case '5': break;
case '6': break;
case '7': break;
default: detect = false;
}
}
if (detect) panel.setBackground(new java.awt.Color(204, 255, 204));
else panel.setBackground(java.awt.Color.RED);
}//GEN-LAST:event_textFieldKeyReleased

/**
* @param args the command line arguments
*/
public static void main(String args[]) {
//java.awt.EventQueue.invokeLater(() -> {
NewJFrame frame = new NewJFrame();
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
//});
}

// Variables declaration - do not modify//GEN-BEGIN:variables
private javax.swing.JPanel panel;
private javax.swing.JTextField textField;
// End of variables declaration//GEN-END:variables
}