Here is an example that change the case of characters to uppercase as the user enters any character.

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

class TextFieldExample extends JFrame{
JTextField text;
JLabel label;
JPanel p;
TextFieldExample(){
text=new JTextField(15);
label=new JLabel("Enter String:");
p=new JPanel();
p.add(label);
p.add(text);
text.addKeyListener(new KeyAdapter(){
            public void keyReleased(KeyEvent e){
                String st=text.getText();
                text.setText(st.toUpperCase());
            }
});
add(p);
setVisible(true);
setSize(300,100);
}
public static void main(String[]args){
TextFieldExample v=new TextFieldExample();
}
}

ok thank you sir