什么是Java原始数据类型修饰符?

Alright, I've been programming in Java for the better part of three years, now, and consider myself very experienced. However, while looking over the Java SE source code, I ran into something I didn't expect:

好吧，我已经用Java编程三年多了，我觉得自己很有经验。然而，在查看Java SE源代码时，我遇到了一些意想不到的东西:

in class Double:

在课堂上双:

public static final double MIN_NORMAL = 0x1.0p-1022; // 2.2250738585072014E-308

public static final double MIN_VALUE = 0x0.0000000000001P-1022; // 4.9e-324

I did not expect this and can't find out what it means. If you don't know, I'm referring to the p and P that are after these numbers, before the subtraction operator. I know you can use suffixes to force a number to be a double, long, float, etc., but I've never encountered a p or P. I checked the Java API, but it doesn't mention it. Is there a complete list of Java primitive number literal modifiers somewhere? Does anyone know them all?

我没有想到这一点，也不知道这是什么意思。如果你不知道，我指的是在这些数字后面的p和p，在减法运算符之前。我知道您可以使用后缀强制一个数字为双精度、长、浮点等，但我从未遇到过p或p。在某个地方有完整的Java原始数字修饰符列表吗?有人认识他们吗?

For reference, below are the ones I've used or encountered, with the ones whose purposes elude me in bold with question marks (# represents any arbitrary number within respective limits):

作为参考，以下是我使用过或遇到过的一些，它们的目的是用粗体用问号标记避开我(#表示在各自范围内的任意数字):

Suffixes:

后缀:

• # = 32-bit integer int
• # = 32位整数int
• #L = 64-bit integer long
• #L = 64位整数长
• #l = another 64-bit integer l?
• #l =另一个64位整数l?
• #f = 32-bit floating-point float
• #f = 32位浮点浮点数。
• #F = another 32-bit floating-point float?
• #F =另一个32位浮点浮点浮点浮点数?
• #d = 64-bit floating-point double
• #d = 64位浮点双精度浮点
• #D = another 64-bit floating-point double?
• 另一个64位浮点双精度浮点?
• #e# = scientific notation
• # # =科学记数法
• #E# = another scientific notation?
• 另一种科学符号?
• #p = ?
• # p = ?
• #P = ?
• # P = ?
• Any more?
• 有更多的吗?

Prefixes:

前缀:

• 0b# = binary (base 2) literal
• 0b# =二进制(以2为基数)文字
• 0B# = another binary (base 2) literal?
• 0B# =另一个二进制(以2为基数)文字?
• 0# = octal (base 8) literal
• 0# =八进制(以8为基数
• # = decimal (base 10) literal
• # =小数(以10为基数)。
• 0x# = hexadecimal (base 16) literal
• 0x# =十六进制(以16为基数)文字
• 0X# = another hexadecimal (base 16) literal?
• 0X# =另一个十六进制(基数16)的文字?
• Any more?
• 有更多的吗?

Other (are there suffixes or prefixes for these?):

其他(有后缀或前缀吗?)

• (byte)# = 8-bit integer byte
• (字节)# = 8位整数字节
• (short)# = 16-bit integer short
• (短)# = 16位整数短
• (char)# - 32-bit character char
• (char)# - 32位字符char

3 个解决方案

#1

P is the exponent. It does not matter if it's capital or not.

P是指数。它是否是资本并不重要。

According to the Javadoc for toHextString (which we know is being used because it begins with 0x:

根据toHextString的Javadoc(我们知道使用toHextString是因为它以0x开头:

public static String toHexString(double d) Returns a hexadecimal string representation of the double argument. All characters mentioned below are ASCII characters. If the argument is NaN, the result is the string "NaN". Otherwise, the result is a string that represents the sign and magnitude of the argument. If the sign is negative, the first character of the result is '-' ('\u002D'); if the sign is positive, no sign character appears in the result. As for the magnitude m:

公共静态字符串toHexString(双d)返回双参数的十六进制字符串表示形式。下面提到的所有字符都是ASCII字符。如果参数是NaN，则结果是字符串“NaN”。否则，结果是一个表示参数符号和大小的字符串。如果符号为负，则结果的第一个字符为'-' ('\u002D');如果符号为正，则结果中不会出现符号字符。至于震级m:

• If m is infinity, it is represented by the string "Infinity"; thus, positive infinity produces the result "Infinity" and negative
  infinity produces the result "-Infinity".

  如果m是无穷大，则用字符串“无穷大”表示;因此，正无穷产生结果“无穷大”，负无穷产生结果“-无穷大”。

• If m is zero, it is represented by the string "0x0.0p0"; thus, negative zero produces the result "-0x0.0p0" and positive zero produces the result "0x0.0p0".

  如果m为0，则用字符串“0x0.0p0”表示;因此，负0产生结果“-0x0.0p0”，正0产生结果“0x0.0p0”。

• If m is a double value with a normalized representation, substrings are used to represent the significand and exponent fields. The significand is represented by the characters "0x1." followed by a lowercase hexadecimal representation of the rest of the significand as a fraction. Trailing zeros in the hexadecimal representation are removed unless all the digits are zero, in which case a single zero is used. Next, the exponent is represented by "p" followed by a decimal string of the unbiased exponent as if produced by a call to Integer.toString on the exponent value.

  如果m是一个具有规范化表示法的双值，则使用子字符串表示含义域和指数域。它的含义是由“0x1”字符表示，后面是小写十六进制表示其余的意义和分数。在十六进制表示法中，除非所有数字都为零，否则将删除末尾的0，在这种情况下，将使用单个0。接下来，指数用“p”表示，后面跟着无偏指数的十进制字符串，就像调用整数一样。表示指数值。

• If m is a double value with a subnormal representation, the significand is represented by the characters "0x0." followed by a hexadecimal representation of the rest of the significand as a fraction. Trailing zeros in the hexadecimal representation are removed. Next, the exponent is represented by "p-1022". Note that there must be at least one nonzero digit in a subnormal significand.

  如果m是一个具有次正态表示法的双值，那么它的意义数由字符“0x0.”表示，然后是一个十六进制表示法，表示其余的意义数。十六进制表示法中的后置零被删除。然后，指数用“p-1022”表示。注意，在次常态的意义数中必须至少有一个非零的数字。

According to the JLS, the following pieces of grammar are accepted:

根据JLS的规定，以下的语法是可以接受的:

3.10.1. Integer Literals

3.10.1。整型常量

IntegerTypeSuffix:

IntegerTypeSuffix:

• l
• l
• L
• l

OctalNumeral:

OctalNumeral:

• 0 OctalDigits
• 0 OctalDigits
• 0 Underscores OctalDigits
• 0强调OctalDigits

HexNumeral:

HexNumeral:

• 0 x HexDigits
• 0 x HexDigits
• 0 X HexDigits
• 0 X HexDigits

BinaryNumeral:

BinaryNumeral:

• 0 b BinaryDigits
• 0 b BinaryDigits
• 0 B BinaryDigits
• 0 B BinaryDigits

3.10.2. Floating-Point Literals

3.10.2。浮点型常量

ExponentIndicator: one of

ExponentIndicator:

• e
• e
• E
• E

FloatTypeSuffix: one of

FloatTypeSuffix:

• f
• f
• F
• F
• d
• d
• D
• D

HexSignificand:

HexSignificand:

• HexNumeral
• HexNumeral
• HexNumeral .
• HexNumeral。
• 0 x HexDigitsopt . HexDigits
• 0 x HexDigitsopt。HexDigits
• 0 X HexDigitsopt . HexDigits
• 0 X HexDigitsopt。HexDigits

BinaryExponentIndicator: one of

BinaryExponentIndicator:

• p
• p
• P
• P

No other single character literals are specified for those purposes.

没有为这些目的指定其他单个字符文字。

#2

All of the legal ways to declare a literal are defined in the JLS.

所有声明文字的合法方法都在JLS中定义。

• p or P is the binary exponent of a number.
• p或p是一个数字的二进制指数。
• l or L defines a long.
• l或l定义了long。
• f or F defines a float.
• f或f定义了一个浮点数。
• d or D defines a double.
• d或d定义了一个double。
• 0B or 0b defines a binary literal.
• 0B或0B定义了二进制文字。
• 0x or 0X defines a hexadecimal literal.
• 0x或0x定义十六进制文字。
• e or E is also an exponent, but since e is a valid character in hexadecimal, p is also used.
• e或e也是一个指数，但由于e在十六进制中是一个有效字符，所以也使用p。

#3

P or p is a BinaryExponentIndicator. See the Java language specification.

P或P是一个二元指数指示器。请参阅Java语言规范。

See http://docs.oracle.com/javase/specs/jls/se5.0/html/lexical.html#3.10.2

看到http://docs.oracle.com/javase/specs/jls/se5.0/html/lexical.html 3.10.2