1 @Beta
 2 @Nullable
 3 @CheckForNull
 4 public static Long tryParse(String string) {
 5   if (checkNotNull(string).isEmpty()) {
 6     return null;
 7   }
   
   
   
   
 8   boolean negative = string.charAt(0) == '-';
 9   int index = negative ? 1 : 0;
10   if (index == string.length()) {
11     return null;
12   }
13   int digit = string.charAt(index++) - '0';
14   if (digit < 0 || digit > 9) {
15     return null;
16   }
17   long accum = -digit;
   
   
   
18   while (index < string.length()) {
19     digit = string.charAt(index++) - '0';
20     if (digit < 0 || digit > 9 || accum < Long.MIN_VALUE / 10) {
21       return null;
22     }
23     accum *= 10;
24     if (accum < Long.MIN_VALUE + digit) {
25       return null;
26     }
27     accum -= digit;
28   }
29 
30   if (negative) {
31     return accum;
32   } else if (accum == Long.MIN_VALUE) {
33     return null;
34   } else {
35     return -accum;
36   }
37 }
38 

 1 @Beta
 2 @Nullable
 3 @CheckForNull
 4 public static Long tryParse(String string, int radix) {
 5   if (checkNotNull(string).isEmpty()) {
 6     return null;
 7   }
 8   if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) {
 9     throw new IllegalArgumentException(
10         "radix must be between MIN_RADIX and MAX_RADIX but was " + radix);
11   }
12   boolean negative = string.charAt(0) == '-';
13   int index = negative ? 1 : 0;
14   if (index == string.length()) {
15     return null;
16   }
17   int digit = digit(string.charAt(index++)) ;
18   if (digit < 0 || digit >= radix) {
19     return null;
20   }
21   long accum = -digit;
22 
23   long cap = Long.MIN_VALUE / radix;
24 
25   while (index < string.length()) {
26     digit = digit(string.charAt(index++));
27     if (digit < 0 || digit >= radix || accum < cap) {
28       return null;
29     }
30     accum *= radix;
31     if (accum < Long.MIN_VALUE + digit) {
32       return null;
33     }
34     accum -= digit;
35   }
36 
37   if (negative) {
38     return accum;
39   } else if (accum == Long.MIN_VALUE) {
40     return null;
41   } else {
42     return -accum;
43   }
44 }
45