Integer源码(parseInt).md

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toUnsignedLong

/**
* 如果x>=0,返回x
* 如果x<0,返回 (2^32-x)
*/
public static long toUnsignedLong(int x) {return ((long) x) & 0xffffffffL;
}

toUnsignedString

/**
* 如果x>=0,返回x
* 如果x<0,返回 (2^32-x)
*/
public static String toUnsignedString(int i) {return Long.toString(toUnsignedLong(i));
}

parseInt

public static int parseInt(String s, int radix)throws NumberFormatException
{if (s == null) {throw new NumberFormatException("null");}//当进制radix<2if (radix < Character.MIN_RADIX) {throw new NumberFormatException("radix " + radix +" less than Character.MIN_RADIX");}//当进制radix>36if (radix > Character.MAX_RADIX) {throw new NumberFormatException("radix " + radix +" greater than Character.MAX_RADIX");}int result = 0;//这是最后要返回的结果boolean negative = false;//符号标志int i = 0, len = s.length();//len--输入字符串s的长度int limit = -Integer.MAX_VALUE; //  -(2^31-1)int multmin;int digit;if (len > 0) {char firstChar = s.charAt(0);//字符串的第一个字符，用于判断是不是负数if (firstChar < '0') { // Possible leading "+" or "-"   '0' == 48if (firstChar == '-') {  //字符 '-' ==  45negative = true;limit = Integer.MIN_VALUE; //如果是负数，那么 limit =  -2^31} else if (firstChar != '+') // '+' == 43throw NumberFormatException.forInputString(s);//如果输入的字符串是 '+'  或者 '-'if (len == 1) // Cannot have lone "+" or "-"throw NumberFormatException.forInputString(s);i++;//待会循环时，就会跳过符号位，从数字开始。}multmin = limit / radix;//这里为什么这么处理？很难懂//下面这个循环是核心，但是超级难懂，以后有机会再回来看吧~~~~~~~~~~while (i < len) {// Accumulating negatively avoids surprises near MAX_VALUEdigit = Character.digit(s.charAt(i++),radix); //把字符转换成 int值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);}return negative ? result : -result;
}

valueOf

//调用的还是上面的parseInt
public static Integer valueOf(String s, int radix) throws NumberFormatException {return Integer.valueOf(parseInt(s,radix));
}

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