比如:parseInt(1010,2)
意思就是:输出2进制数1010在十进制下的数.
更直白地说: parseInt(String s,int radix)就是求“int radix”进制数“String s”的十进制数是多少。
-----------------------
我们平时用到Integer.parseInt("123");其实默认是调用了int i =Integer.parseInt("123",10);
其中10代表的默认是10进制的,转换的过程可以看成:
i= 1*10*10+2*10+3
若是
int i = Integer.parseInt("123",16);
即可以看成:
i = 1*16*16+2*16+3 = 291
根据:Character.MIN_RADIX=2和Character.MAX_RADIX=36 则,parseInt(String s, int radix)参数中
radix的范围是在2~36之间,超出范围会抛异常。其中s的长度也不能超出7,否则也会抛异常。
源码如下:
public static int parseInt(String s, int radix) throws NumberFormatException { if (s == null) { throw new NumberFormatException("null"); } if (radix < Character.MIN_RADIX) { throw new NumberFormatException("radix " + radix + " less than Character.MIN_RADIX"); } if (radix > Character.MAX_RADIX) { throw new NumberFormatException("radix " + radix + " greater than Character.MAX_RADIX"); } int result = 0; boolean negative = false; int i = 0, max = s.length(); int limit; int multmin; int digit; if (max > 0) { if (s.charAt(0) == '-') { negative = true; limit = Integer.MIN_VALUE; i++; } else { limit = -Integer.MAX_VALUE; } multmin = limit / radix; if (i < max) { digit = Character.digit(s.charAt(i++),radix); if (digit < 0) { throw NumberFormatException.forInputString(s); } else { result = -digit; } } while (i < max) { // Accumulating negatively avoids surprises near MAX_VALUE digit = Character.digit(s.charAt(i++),radix); if (digit < 0) { throw NumberFormatException.forInputString(s); } if (result < multmin) { throw NumberFormatException.forInputString(s); } result *= radix; if (result < limit + digit) { throw NumberFormatException.forInputString(s); } result -= digit; } } else { throw NumberFormatException.forInputString(s); } if (negative) { if (i > 1) { return result; } else { /* Only got "-" */ throw NumberFormatException.forInputString(s); } } else { return -result; } }
网络摘录