Here is an example that validates single field. You can validate other fields in the same way.

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class SwingProgram{
public static void main(String args[]){
SwingProgram p=new SwingProgram();
}
public SwingProgram(){
JLabel label=new JLabel("Enter Name:");
final JTextField text=new JTextField(15);
JButton button=new JButton("Submit");
JFrame f=new JFrame();
f.getContentPane().setLayout(null);
label.setBounds(50,50,80,20);
text.setBounds(150,50,150,20);
button.setBounds(50,80,80,20);
f.add(label);
f.add(text);
f.add(button);
f.setSize(400,150);
f.setVisible(true);
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
String name=text.getText();
if((name.equals(""))||(name.equals(null))){
JOptionPane.showMessageDialog(null,"Please enter the field","Error",JOptionPane.ERROR_MESSAGE);
}
else{
JOptionPane.showMessageDialog(null,"Welcome "+name);
}
}
});
}
}