Here you can find the source of charAt(CharSequence chars, int index, boolean ignoreCase)
private static final char charAt(CharSequence chars, int index, boolean ignoreCase)
//package com.java2s; public class Main { private static final char charAt(String chars, int index, boolean ignoreCase) { return (ignoreCase ? Character.toLowerCase(chars.charAt(index)) : chars.charAt(index)); }/*from w w w . j a v a 2 s. c om*/ private static final char charAt(CharSequence chars, int index, boolean ignoreCase) { return (ignoreCase ? Character.toLowerCase(chars.charAt(index)) : chars.charAt(index)); } }