Java——String.split()函数

在java doc里有

  String[] java. lang. String.split( String regex)

Splits this string around matches of the given regular expression.

This method works as if by invoking the two-argument split method with the given expression and a limit argument of zero. Trailing empty strings are therefore not included in the resulting array.

The string "boo:and:foo", for example, yields the following results with these expressions:

Regex	Result
:	{ "boo", "and", "foo" }
o	{ "b", "", ":and:f" }

Parameters:

regex the delimiting regular expression

Returns:

the array of strings computed by splitting this string around matches of the given regular expression

Throws:

PatternSyntaxException - if the regular expression's syntax is invalid

Since:

1.4

See Also:

java.util.regex.Pattern

@spec

JSR-51

但是要注意以下几点：

(1)如果用“.”作为分隔的话必须是如下写法String.split("\\."),这样才

能正确的分隔开不能用String.split(".");

比如这段代码：

	String str="123.456";

	String []arrStr=str.split(".");

	System.out.println(arrStr.length);

结果为：

而：

	String str="123.456";

	String []arrStr=str.split("\\.");

	System.out.println(arrStr.length);

结果为：

　

原因是

Splits this string around matches of the given regular expression.要求的是一个正则表达式所以必须满足正则表达式的形式，

因此需要进行转义才行。

下面给出split()函数的源代码供参考：

 public String[] split(String regex, int limit) {

        /* fastpath if the regex is a

         (1)one-char String and this character is not one of the

            RegEx's meta characters ".$|()[{^?*+\\", or

         (2)two-char String and the first char is the backslash and

            the second is not the ascii digit or ascii letter.

         */

        char ch = 0;

        if (((regex.value.length == 1 &&

             ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||

             (regex.length() == 2 &&

              regex.charAt(0) == '\\' &&

              (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&

              ((ch-'a')|('z'-ch)) < 0 &&

              ((ch-'A')|('Z'-ch)) < 0)) &&

            (ch < Character.MIN_HIGH_SURROGATE ||

             ch > Character.MAX_LOW_SURROGATE))

        {

            int off = 0;

            int next = 0;

            boolean limited = limit > 0;

            ArrayList<String> list = new ArrayList<>();

            while ((next = indexOf(ch, off)) != -1) {

                if (!limited || list.size() < limit - 1) {

                    list.add(substring(off, next));

                    off = next + 1;

                } else {    // last one

                    //assert (list.size() == limit - 1);

                    list.add(substring(off, value.length));

                    off = value.length;

                    break;

                }

            }

            // If no match was found, return this

            if (off == 0)

                return new String[]{this};



            // Add remaining segment

            if (!limited || list.size() < limit)

                list.add(substring(off, value.length));



            // Construct result

            int resultSize = list.size();

            if (limit == 0)

                while (resultSize > 0 && list.get(resultSize - 1).length() == 0)

                    resultSize--;

            String[] result = new String[resultSize];

            return list.subList(0, resultSize).toArray(result);

        }

        return Pattern.compile(regex).split(this, limit);

    }

　　public String[] split(String regex) {
　　return split(regex, 0);
　　}