java 实现旋转字符串

给定一个字符串，要求把字符串前面的若干个字符移动到字符串的尾部如把字符串“abcdef”前面的2个字符'a'和'b'移动到字符串的尾部，使得原字符串变成字符串“cdefab”。目前的思路是：将字符串拼接一倍：如str1=abcdef拼接成str2=abcdefabcdef,然后取新拼接字符串(str2)的子字符串，长度为原来的字符串(str1)长度。具体用java中的java.lang.String库中的subSequence()函数 <无> .CodeEntity .code_pieces ul.piece_anchor{width:25px;position:absolute;top:25px;left:-30px;z-index:1000;}.CodeEntity .code_pieces ul.piece_anchor li{width:25px;background: #efe;margin-bottom:2px;}.CodeEntity .code_pieces ul.piece_anchor li{border-left:3px #40AA63 solid;border-right:3px #efe solid;}.CodeEntity .code_pieces ul.piece_anchor li:hover{border-right:3px #40AA63 solid;border-left:3px #efe solid;}.CodeEntity .code_pieces ul.piece_anchor li a{color: #333;padding: 3px 10px;}.CodeEntity .code_pieces .jump_to_code{visibility:hidden;position:relative;}.CodeEntity .code_pieces .code_piece:hover .jump_to_code{visibility:visible;}.CodeEntity .code_pieces .code_piece:hover .jump_to_code a{text-decoration:none;}.CodeEntity .code_pieces h2 i{float:right;font-style:normal;font-weight:normal;}.CodeEntity .code_pieces h2 i a{font-size:9pt;background: #FFFFFF;color:#00A;padding: 2px 5px;text-decoration:none;}