JFrame: How to disable window resizing?

I am creating a JFrame and I call the method setSize(500, 500). Now the desired behaviour is that JFrame should not be resized by user in any condition. Either by maximizing or by dragging the borders. It should be 500x500. How can I do it? I have also attached the code in case you can guide me better.

    package com.techpapa;    
    import javax.swing.*;  
    import java.awt.*;  
    import java.awt.event.*;  

    public class MainWindow extends JFrame{


private JTextField
            write;
private JRadioButton
            rb1,
            rb2,
            rb3;
private ButtonGroup
            bg;

private ActionListener al = new ActionListener(){
    public void actionPerformed(ActionEvent e){
        write.setText("JRadioButton : " + ((JRadioButton)e.getSource()).getText());
    }

};

public MainWindow(){
    //Frame Initialization
    setSize(500, 500);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setLayout(null);
    setTitle(".:JRadioButton:.");
    setVisible(true);

    //Components Initialization
    write = new JTextField(20);
    write.setEditable(false);
    rb1 = new JRadioButton("Male", false);
    rb1.addActionListener(al);
    rb2 = new JRadioButton("Female", false);
    rb2.addActionListener(al);
    rb3 = new JRadioButton("I don't want to specify", true);
    rb3.addActionListener(al);
    bg = new ButtonGroup();

    //Add radio buttons to buttongroup
    bg.add(rb1); bg.add(rb2); bg.add(rb3);

    //Add to window
    add(write);
    write.setBounds(140, 100, 150, 20);
    write.setDragEnabled(true);
    add(rb1);
    rb1.setBounds(180, 200, 100, 30);
    add(rb2);
    rb2.setBounds(180, 225, 100, 30);
    add(rb3);
    rb3.setBounds(180, 250, 130, 30);

}

public static void main(String[] args) {
    new MainWindow();

}

}

You can use a simple call in the constructor under "frame initialization":

setResizable(false);

After this call, the window will not be resizable.