Here you can find the source of length(Object string)
public static final int length(Object string)
//package com.java2s; /*/*from w w w . ja v a2s . c o m*/ * This file is part of the Jose Project * see http://jose-chess.sourceforge.net/ * (c) 2002-2006 Peter Sch?fer * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * */ public class Main { public static final int length(Object string) { if (string instanceof String) return ((String) string).length(); if (string instanceof StringBuffer) return ((StringBuffer) string).length(); throw new IllegalArgumentException("expecting String or StringBuffer"); } }