Check out example codes for "upper en java". It will help you in understanding the concepts better.

Code Example 1

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());   
    }
}

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