java - Integer.parseInt はどのように機能しますか

Question

メソッド public static int parseInt(String str) および public static int parseInt(String str, int redix)

それはどのように機能しますか？

＆それらの違いは何ですか？

Answer 1

You can read the implementation here. And the documentation here.

As for the difference:

The first assumes the String to be a decimal representation, while the second expects another parameter which is the base of the representation (binary, hex, decimal etc.)

( parseInt(String str) is implemented as return parseInt(str, 10))

Answer 2

ああ、Java はオープン ソースです。JDK6の整数から：

 /**
 * Parses the specified string as a signed decimal integer value. The ASCII
 * character \u002d ('-') is recognized as the minus sign.
 *
 * @param string
 *            the string representation of an integer value.
 * @return the primitive integer value represented by {@code string}.
 * @throws NumberFormatException
 *             if {@code string} cannot be parsed as an integer value.
 */
public static int parseInt(String string) throws NumberFormatException {
    return parseInt(string, 10);
}

そして基数で：

/**
 * Parses the specified string as a signed integer value using the specified
 * radix. The ASCII character \u002d ('-') is recognized as the minus sign.
 *
 * @param string
 *            the string representation of an integer value.
 * @param radix
 *            the radix to use when parsing.
 * @return the primitive integer value represented by {@code string} using
 *         {@code radix}.
 * @throws NumberFormatException
 *             if {@code string} cannot be parsed as an integer value,
 *             or {@code radix < Character.MIN_RADIX ||
 *             radix > Character.MAX_RADIX}.
 */
public static int parseInt(String string, int radix) throws NumberFormatException {
    if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) {
        throw new NumberFormatException("Invalid radix: " + radix);
    }
    if (string == null) {
        throw invalidInt(string);
    }
    int length = string.length(), i = 0;
    if (length == 0) {
        throw invalidInt(string);
    }
    boolean negative = string.charAt(i) == '-';
    if (negative && ++i == length) {
        throw invalidInt(string);
    }

    return parse(string, i, radix, negative);
}

Answer 3

They are basically the same function. parseInt(String str) assumes base-10 (unless the string starts with 0x or 0). parseInt(String str, int radix) uses the given base. I haven't looked at the code but I bet the first simply calls parseInt(str, 10) (except in those two special cases where it'll use 16 and 8).