关于Integer的parseInt(String s, int radix)方法的使用
最近看了一些别人写的java程序,其中就用到Integer.parseInt("23f34d",16);这个方法,当时很不解。
在网上搜了一下,才明白原来是这样的。
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首先可以看一下jdk中 java.lang.Integer中的源码如下:
public static int parseInt(String s) throws NumberFormatException {return parseInt(s,10); }?
public static int parseInt(String s, int radix)throws NumberFormatException { if (s == null) { throw new NumberFormatException("null"); }if (radix < Character.MIN_RADIX) { //Character.MIN_RADIX=2 throw new NumberFormatException("radix " + radix + " less than Character.MIN_RADIX");}if (radix > Character.MAX_RADIX) { //Character.MAN_RADIX=36 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_VALUEdigit = 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;} }
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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。