代码来源于 https://svn.apache.org/repos/asf/harmony/enhanced/classlib/archive/java6/modules/luni/src/main/java/java/lang/Integer.java
public static int parseInt(char[] chars) { return parseInt(chars, 0, chars.length); } public static int parseInt(char[] chars, int offset, int length) { return parseInt(chars, offset, length, 10); } public static int parseInt(char[] chars, int offset, int length, int radix) throws NumberFormatException { if (chars == null || radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) { throw new NumberFormatException(); } if (length == 0) { throw new NumberFormatException("Unable to parse"); } int i = 0; boolean negative = (chars[i + offset] == '-'); if (negative && ++i == length) throw new NumberFormatException("Unable to parse"); if (negative) { offset++; length--; } return parseInt(chars, offset, length, radix, negative); } /** * 这个方法把要解析的字符数组映射到了负数的范围内。因为java int 的取值范围是 -2^32 ~ 2^31,负数的取值范围比正数要大 * @param chars 字符数组 * @param offset 有效的字符起始 idx * @param len 有效字符长度 * @param radix 基数,比如 10 进制,2 进制啥的 * @param negative 这个数是不是负数 * @return * @throws NumberFormatException */ public static int parseInt(char[] chars, int offset, int len, int radix, boolean negative) throws NumberFormatException { //这里的 max 取值是负数,下面解析出来的数都是负数。这里的 max 是绝对值最大,而不是实际值最大 int max = Integer.MIN_VALUE / radix; int result = 0; for (int i = 0; i < len; i++) { //解析出来的第一个数字 int digit = Character.digit(chars[i + offset], radix); if (digit == -1) { throw new NumberFormatException("Unable to parse"); } if (max > result) { throw new NumberFormatException("Unable to parse"); } //映射到负数的范围内,解析出来的数字要被减去。next 的值要比已经保存的值(next) 小 int next = result * radix - digit; if (next > result) { throw new NumberFormatException("Unable to parse"); } result = next; } if (!negative) { result = -result; if (result < 0) { throw new NumberFormatException("Unable to parse"); } } return result; }