Java中Integer的parseInt和valueOf的区别详解

String str = "1";
System.out.println(Integer.valueOf(str));//1
System.out.println(Integer.parseInt(str));//1

public static int parseInt(String s, int radix) throws NumberFormatException {
        /* 警告：在初始化IntegerCache之前，VM初始化期间可能会提前调用此方法。
         * 必须注意不要使用valueOf方法。
         * WARNING: This method may be invoked early during VM initialization
         * before IntegerCache is initialized. Care must be taken to not use
         * the valueOf method.
         */
        //字符串为空则抛出NumberFormatException
        if (s == null) {
            throw new NumberFormatException("null");
        }
        //传的进制参数小于2，抛出NumberFormatException，
        //并且提示进制小于最小进制
        if (radix < Character.MIN_RADIX) {
            throw new NumberFormatException("radix " + radix +
                    " less than Character.MIN_RADIX");
        }
        //传的进制参数大于36，抛出NumberFormatException，
        //并且提示进制大于最大进制
        if (radix > Character.MAX_RADIX) {
            throw new NumberFormatException("radix " + radix +
                    " greater than Character.MAX_RADIX");
        }
        int result = 0;
        //negative 用来判断结果是否为负数
        boolean negative = false;
        //获取字符串长度
        int i = 0, len = s.length();
        //limit = -2147483647
        int limit = -Integer.MAX_VALUE;
        //用于在添加下一位数字的前判断是否溢出的值
        int multmin;
        //需要追加的数字
        int digit;
        //字符长度大于0
        if (len > 0) {
            //判断字符串是否有符号
            char firstChar = s.charAt(0);
            if (firstChar < '0') { // Possible leading "+" or "-"
                if (firstChar == '-') {
                    //第一个符号是负号，所以结果是负数
                    negative = true;
                    limit = Integer.MIN_VALUE;
                } else if (firstChar != '+')
                    //不为负数或正数，抛出NumberFormatException
                    throw NumberFormatException.forInputString(s);
                //长度为1，抛出NumberFormatException
                if (len == 1) // Cannot have lone "+" or "-"
                    throw NumberFormatException.forInputString(s);
                i++;
            }
            //计算 multmin ，注意负数和正数的limit是不一样的,
            //负数的limit = -2147483648，正数的limit = -2147483647
            multmin = limit / radix;
            while (i < len) {
                // 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 {
            //字符不为空，但是字符长度等于0，抛出NumberFormatException
            throw NumberFormatException.forInputString(s);
        }
        //根据正负数的标识来判断结果取正还是取反
        return negative ? result : -result;
    }