题目要求：将String字符串转换成数字，不能用java自带的方法转换字符串，要求自己写一个atoi(String s)，如果输入的不是数字则返回0。

import java.util.Scanner;/** * Created by Dell on 2014/7/14. * * 面试题 * 将字符串转换成数字，不用java自带的方法 */public class MianShi_01 {    public static void main(String[] args) {        Scanner input = new Scanner(System.in);        System.out.print("str = ");        String str = input.nextLine();        System.out.println(new MianShi_01().atoi(str));    }    public int atoi(String s) {        int[] num = new int[10];        int j = 0;        String tmp = null;        for (int i = 0; i < s.length(); i++) {            if (s.charAt(0) == '-' || Character.isDigit(s.charAt(i))) {                if (s.charAt(0) == '-') {                    tmp = "-";                }                switch (s.charAt(i)) {                    case '0':                        num[j] = 0;                        j++;                        continue;                    case '1':                        num[j] = 1;                        j++;                        continue;                    case '2':                        num[j] = 2;                        j++;                        continue;                    case '3':                        num[j] = 3;                        j++;                        continue;                    case '4':                        num[j] = 4;                        j++;                        continue;                    case '5':                        num[j] = 5;                        j++;                        continue;                    case '6':                        num[j] = 6;                        j++;                        continue;                    case '7':                        num[j] = 7;                        j++;                        continue;                    case '8':                        num[j] = 8;                        j++;                        continue;                    case '9':                        num[j] = 9;                        j++;                        continue;                }            }            else {                return 0;            }        }        int NUM = (int) Math.pow(10, j);        int a = 0;        for (int i = 0; i < num.length; i++) {            NUM = NUM / 10;            a += num[i] * NUM;        }        if (tmp != null) {            return -a;        }        return a;    }}