Java字符串滚动的编写，效果如下：

开始：
abcdefg
之后是
bcdefga
之后是
cdefgab
...

String str = "abcdefg";
for(int i=1;i<str.length;i++){
   System.out.print(str.substring(i)+str.substring(0,1);
}

String before = "abcdefg";
for (int i = 0; i < 3; i++) {
        String end = before.substring(1) + before.substring(0, 1);
        System.out.println(end);
        before = end;
}