如何使用某些分隔符拆分String但不在Java中删除该分隔符？ [英] How to split String with some separator but without removing that separator in Java?

问题描述

我在拆分字符串时遇到问题。

我想拆分 String 带有一些分隔符，但不会丢失该分隔符。

I want to split a String with some separator but without losing that separator.

当我们使用 somestring.split（String separator） Java中的方法它会拆分 String ，但会从 String 中删除​​分隔符部分。我不希望这种情况发生。

When we use somestring.split(String separator) method in Java it splits the String but removes the separator part from String. I don't want this to happen.

我想要如下结果：

String string1="Ram-sita-laxman";
String seperator="-";
string1.split(seperator);

输出：

[Ram, sita, laxman]

但我希望结果如下所示相反：

but I want the result like the one below instead:

[Ram, -sita, -laxman]

有没有办法得到这样的输出？

Is there a way to get output like this?

推荐答案

string1.split("(?=-)");

这可行，因为 split 实际需要< a href =http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html>正则表达式。你实际看到的是零宽度正向前瞻。

This works because split actually takes a regular expression. What you're actually seeing is a "zero-width positive lookahead".

我想解释更多，但我女儿想参加茶话会。 ：）

I would love to explain more but my daughter wants to play tea party. :)

编辑：返回！

为了解释这一点，我会先说显示不同的拆分操作：

To explain this, I will first show you a different split operation:

"Ram-sita-laxman".split("");

这会在每个零长度字符串上拆分字符串。每个字符之间都有一个零长度的字符串。因此，结果是：

This splits your string on every zero-length string. There is a zero-length string between every character. Therefore, the result is:

["", "R", "a", "m", "-", "s", "i", "t", "a", "-", "l", "a", "x", "m", "a", "n"]

现在，我修改我的正则表达式（）以仅匹配零长度字符串如果后跟短划线。

Now, I modify my regular expression ("") to only match zero-length strings if they are followed by a dash.

"Ram-sita-laxman".split("(?=-)");
["Ram", "-sita", "-laxman"]

例如，？= 表示前瞻。更具体地说，它意味着积极的先行。为什么积极？因为您还可以否定预测（？！），它将在不的每个零长度字符串上拆分然后是破折号：

In that example, the ?= means "lookahead". More specifically, it mean "positive lookahead". Why the "positive"? Because you can also have negative lookahead (?!) which will split on every zero-length string that is not followed by a dash:

"Ram-sita-laxman".split("(?!-)");
["", "R", "a", "m-", "s", "i", "t", "a-", "l", "a", "x", "m", "a", "n"]

您还可以拥有积极的外观（？< = ），它将在每个零长度字符串上分割，前面有一个破折号：

You can also have positive lookbehind (?<=) which will split on every zero-length string that is preceded by a dash:

"Ram-sita-laxman".split("(?<=-)");
["Ram-", "sita-", "laxman"]

最后，你也可以有负面的背后隐藏（？<！），它会在不以破折号开头：

Finally, you can also have negative lookbehind (?<!) which will split on every zero-length string that is not preceded by a dash:

"Ram-sita-laxman".split("(?<!-)");
["", "R", "a", "m", "-s", "i", "t", "a", "-l", "a", "x", "m", "a", "n"]

这四个表达式统称为 lookaround 表达式。

These four expressions are collectively known as the lookaround expressions.

我只想展示一个我最近遇到的结合了两个外观表达式的例子。假设您希望将CapitalCase标识符拆分为其标记：

I just wanted to show an example I encountered recently that combines two of the lookaround expressions. Suppose you wish to split a CapitalCase identifier up into its tokens:

"MyAwesomeClass" => ["My", "Awesome", "Class"]

您可以使用此正则表达式完成此操作：

You can accomplish this using this regular expression:

"MyAwesomeClass".split("(?<=[a-z])(?=[A-Z])");

这会在每个零长度字符串上拆分，前面带有小写字母（（？< = [az]））后跟一个大写字母（（？= [AZ]））。

This splits on every zero-length string that is preceded by a lower case letter ((?<=[a-z])) and followed by an upper case letter ((?=[A-Z])).

此技术也适用于camelCase标识符。

This technique also works with camelCase identifiers.

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