JavaSE－将字符串转换为数字

import java.util.*;
public class Solution {
    /**
     * 
     * @param str string字符串 
     * @return int整型
     */
  public  int atoi(String str) {
		if (str == null || str.trim().length() < 1)
			return 0;
		char[] c = str.trim().toCharArray();
		int sign = 1;
		int index = 0;
		if (c[0] == '+')
			index++;
		if (c[0] == '-') {
			sign = -1;
			index++;
		}
		int num = 0;
		for (int i = index; i < c.length; i++) {
			if (c[i] - '0' >= 0 && c[i] - '9' <= 0) {
				if (num > Integer.MAX_VALUE / 10 || num == Integer.MAX_VALUE / 10 && c[i] - '7' > 0) {
					if (sign > 0)
						return Integer.MAX_VALUE;
					else
						return Integer.MIN_VALUE;
				}
				num = 10 * num + c[i] - '0';
			} else
				break;
		}
		return num * sign;
	}
}