倒序输出一组字符串。例如输入：“478.abc”，输出：“cba.874”

public class Test {

    public String getReturnNum(String num){
            StringBuffer sb = new StringBuffer();
            while(num.length() > 0){
            sb.append(num.charAt(num.length() - 1));
            num = (String) num.subSequence(0, num.length() - 1);
        }
        return sb.toString();
    }

    public static void main(String[] args) {
        Test t = new Test();
        String num = "478.abc";
        System.out.println(t.getReturnNum(num));
    }

}

打印结果：cba.874

如果不明白，可以单独测试String的下面几个方法就明白了：

charAt(int i);

subSequence(int begin, int end);