Java String with only lower case characters

//package com.demo2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        String str = "";
        System.out.println(allLowerCase(str));
    }//from  w w  w.jav a 2 s  .c  om

    public static boolean allLowerCase(String str) {
        String lowerCased = str.toLowerCase();
        return str.equals(lowerCased);
    }
}