Here you can find the source of toLowerCase(final char a)
public static char toLowerCase(final char a)
//package com.java2s; public class Main { public static char toLowerCase(final char a) { if (a < 'A' || a >= 'a' && a <= 'z') { return a; }/*from www . j a va 2s.c o m*/ if (a >= 'A' && a <= 'Z') { return (char) (a + ('a' - 'A')); } return Character.toLowerCase(a); } }