Thread: Whats wrong with my code?

import javax.swing.*;
 
public class AnimateJInternalFrame {
 
    JFrame jf=new JFrame();
    JInternalFrame jif=new JInternalFrame();
    Timer t;
 
    public AnimateJInternalFrame() {
 
        jf.setSize(700,700);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setLayout(null);
 
 
        jif.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jif.setLayout(null);
        jif.setBounds(50,50,300,300);
 
 
        jf.setVisible(true);
        jf.add(jif);
 
        t=new Timer(30,null);
        t.start();
        for(int i=50;i<500;i++){
            jif.setBounds(50,i,300,300);
            jif.setVisible(true);
            }
 
    }
    public static void main(String[] args) {
        new AnimateJInternalFrame();
 
    }
 
}

I want that JInternalFrame to animate smoothly downwards but it is'nt working.

Whats the problem with my code?