Use toUpperCase() method to convert the string in uppercase letters.

class UppercaseString 
{
    public static void main(String[] args) 
    {
        String st="Hello";
        String upperSt=st.toUpperCase();
        System.out.println(upperSt);
    }
}

import javax.swing.*;

class UppercaseString 
{
    public static void main(String[] args) 
    {
        JFrame f=new JFrame();
        String st="Hello";
        String upperSt=st.toUpperCase();
        f.setTitle(upperSt);
        f.setVisible(true);
        f.add(new JLabel("Welcome"));
        f.setSize(300,100);
    }
}