Validate 4 JTextfield (from being empty)

Question

hello , i'm new using java ,i've done a method that work fine , but due to my lack of knowledge of the language , the method is to big( in lines of code) , i know i could use a "for" and inside an "if" to make the validation , but i dont understand the behavior of the objects . here is the code
public void actionPerformed (ActionEvent ae ) {
Object obj = ae.getSource();
if (obj == BTGuarPre){ //BTGuarPre IS COMMAND  BUTTON
verificar (obj);
void verificar (Object obj){
if (TXT1.getText().equals("")) {
JOptionPane.showMessageDialog (this,
"Por favor Introduce Una Respuesta.",
     "Campo Vacio", JOptionPane.PLAIN_MESSAGE);
               TXT1.requestFocus();
          } else if (TXT2.getText().equals("")) {
JOptionPane.showMessageDialog (this,
               "Por favor Introduce Una Respuesta.",
               " Campo Vacio", JOptionPane.PLAIN_MESSAGE);
               TX2.requestFocus();
     } else if (TXT3.getText().equals("")) {
               JOptionPane.showMessageDialog (this,
               "Por favor Introduce Una Respuesta.",
               " Campo Vacio", JOptionPane.PLAIN_MESSAGE);
               TXT3.requestFocus();
          } else if (TXT4.getText().equals("")) {
     JOptionPane.showMessageDialog (this,
     "Por favor Introduce Una Respuesta.",
               " Campo Vacio", JOptionPane.PLAIN_MESSAGE);
               T4.requestFocus();
} else {
bla,bla
thank s !!!

Answer 1

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class NumericVerifier
public static void main(String args[])
JFrame frame = new JFrame("Numeric Verifier");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel1 = new JPanel(new BorderLayout());
JLabel label1 = new JLabel("Numeric-only");
JTextField textField1 = new JTextField();
panel1.add(label1, BorderLayout.WEST);
panel1.add(textField1, BorderLayout.CENTER);
JPanel panel3 = new JPanel(new BorderLayout());
JLabel label3 = new JLabel("Numeric-only");
JTextField textField3 = new JTextField();
panel3.add(label3, BorderLayout.WEST);
panel3.add(textField3, BorderLayout.CENTER);
InputVerifier verifier = new InputVerifier()
public boolean verify(JComponent comp)
boolean returnValue;
JTextField textField = (JTextField)comp;
try
Integer.parseInt(textField.getText());
returnValue = true;
} catch (NumberFormatException e)
returnValue = false;
return returnValue;
textField1.setInputVerifier(verifier);
textField3.setInputVerifier(verifier);
frame.add(panel1, BorderLayout.NORTH);
//frame.add(panel2, BorderLayout.CENTER);
frame.add(panel3, BorderLayout.SOUTH);
frame.setSize(300, 95);
frame.setVisible(true);
TRY THIS
Thanx