java string uppercase

public class Guru99 {   
    public static void main(String args[]) {       
        String S1 = new String("minúsculas convertidas en mayúsculas");       
 
        // Convertir a UpperCase    
        System.out.println(S1.toUpperCase());   
    }
}

string s="hello";
s = Character.toUpperCase(s.charAt(0)) + s.substring(1);
The output will be: Hello

String txt = "Hello World";
System.out.println(txt.toUpperCase());
System.out.println(txt.toLowerCase());