問題描述

是否有一種本地方式(最好不實現自己的方法)來檢查字符串是否可以用 Double.parseDouble() 解析?

Is there a native way (preferably without implementing your own method) to check that a string is parseable with Double.parseDouble()?

推薦答案

常見的方法是使用正則表達式檢查它，就像 Double.valueOf(String) 文檔.

The common approach would be to check it with a regular expression like it's also suggested inside the Double.valueOf(String) documentation.

那里提供(或包含在下面)的正則表達式應該涵蓋所有有效的浮點情況，所以你不需要擺弄它，因為你最終會錯過一些更好的點.

The regexp provided there (or included below) should cover all valid floating point cases, so you don't need to fiddle with it, since you will eventually miss out on some of the finer points.

如果您不想這樣做，try catch 仍然是一種選擇.

If you don't want to do that, try catch is still an option.

JavaDoc 建議的正則表達式如下:

The regexp suggested by the JavaDoc is included below:

final String Digits     = "(\p{Digit}+)";
final String HexDigits  = "(\p{XDigit}+)";
// an exponent is 'e' or 'E' followed by an optionally 
// signed decimal integer.
final String Exp        = "[eE][+-]?"+Digits;
final String fpRegex    =
    ("[\x00-\x20]*"+ // Optional leading "whitespace"
    "[+-]?(" +         // Optional sign character
    "NaN|" +           // "NaN" string
    "Infinity|" +      // "Infinity" string

    // A decimal floating-point string representing a finite positive
    // number without a leading sign has at most five basic pieces:
    // Digits . Digits ExponentPart FloatTypeSuffix
    // 
    // Since this method allows integer-only strings as input
    // in addition to strings of floating-point literals, the
    // two sub-patterns below are simplifications of the grammar
    // productions from the Java Language Specification, 2nd 
    // edition, section 3.10.2.

    // Digits ._opt Digits_opt ExponentPart_opt FloatTypeSuffix_opt
    "((("+Digits+"(\.)?("+Digits+"?)("+Exp+")?)|"+

    // . Digits ExponentPart_opt FloatTypeSuffix_opt
    "(\.("+Digits+")("+Exp+")?)|"+

    // Hexadecimal strings
    "((" +
    // 0[xX] HexDigits ._opt BinaryExponent FloatTypeSuffix_opt
    "(0[xX]" + HexDigits + "(\.)?)|" +

    // 0[xX] HexDigits_opt . HexDigits BinaryExponent FloatTypeSuffix_opt
    "(0[xX]" + HexDigits + "?(\.)" + HexDigits + ")" +

    ")[pP][+-]?" + Digits + "))" +
    "[fFdD]?))" +
    "[\x00-\x20]*");// Optional trailing "whitespace"

if (Pattern.matches(fpRegex, myString)){
    Double.valueOf(myString); // Will not throw NumberFormatException
} else {
    // Perform suitable alternative action
}

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