回文

[实验任务二]：递归方法
（1）    使用递归方式判断某个字串是否是回文（ palindrome ）；
“回文”是指正着读、反着读都一样的句子。比如“我是谁是我”
使用递归算法检测回文的算法描述如下：
A single or zero-character string is a palindrome.
Any other string is a palindrome if the first and last characters are the same, and the string that remains, excepting those characters, is a palindrome.

package palindrome;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
/*
 * 使用递归方式判断某个字串是否是回文（ palindrome ）
 * 从文件中读入
 */
public class palindrome {
     
    public static void main(String[] args) throws IOException {
        String url = "test.txt";
        File file = new File(url);// 指定操作文件
        if (!file.exists() || file.isDirectory()) {
            System.out.println("文件不存在！");
            return;
        } else
            System.out.println("文件导出成功");
        StringBuffer sb0 = new StringBuffer();
        BufferedReader br;
        try {
            br = new BufferedReader(new FileReader(file));
            String temp = null;
            //sb = new StringBuffer();
            temp = br.readLine();
            while (temp != null) {
                sb0.append(temp + "\r");
                temp = br.readLine();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        String sb = sb0.toString();
        boolean flag = find(sb,0,sb.length());
        
        System.out.println(flag);
    }
 
    private static boolean find(String sb, int start, int length) {
        
        if(length<=1)
            return true;
        else if(sb.toCharArray()[start]==sb.toCharArray()[length-1]){
            return find(sb,start+1,length-1);
        }
        return false;
    }
}