java find duplicate characters in a string

/**
 * @author lautturi.com 
 * Java example:search duplicate characters in a string
 */

import java.util.Set;
import java.util.HashSet;

public class Lautturi {

	public static void main(String[] args) {

		String str = "Hello Java";
		for (int i = 0; i < str.length(); i++) {
			for (int j = i + 1; j < str.length(); j++) {
				if (str.charAt(i) == str.charAt(j)) {
					System.out.println("duplicate character: "+str.charAt(i) + " ");
					break;
				}
			}
		}
	}

}

output:

duplicate character: l 
duplicate character: a