String to Integer (atoi)

 1 private static final int maxDiv10 = Integer.MAX_VALUE / 10;
 2 
 3 public int atoi(String str) {
 4     int i = 0;
 5     int n = str.length();
 6     // 首先忽略字符串前面的空格
 7     while(i < n && Character.isWhitespace(str.charAt(i))) {
 8         i++;
 9     }
10 
11     int sign = 1;
12     if(i < n && str.charAt(i) == ‘+‘) {
13         i++;
14     } else if(i < n && str.charAt(i) == ‘-‘) {
15         sign = -1;
16         i++;
17     }
18 
19     int num = 0;
20     while(i < n && Character.isDigit(str.charAt(i))) {
21         int digit = Character.getNumericValue(str.charAt(i));
22         if(num > maxDiv10 || num == maxDiv10 && digit >= 8) {
23             return sign == 1?Integer.MAX_VALUE:Integer.MIN_VALUE;
24         }
25 
26         num = num * 10 + digit;
27         i++;
28     }
29 
30     return sign * num;
31 }