String.split（）处于元字符+ [英] String.split() at a meta character +

问题描述

我正在编写一个简单的程序来处理方程式的字符串输入中的方程式
然而，当我运行它时，我得到一个例外，因为我试图用+替换+ 所以我可以在空格处拆分字符串。我该如何使用

I'm making a simple program that will deal with equations from a String input of the equation When I run it, however, I get an exception because of trying to replace the " +" with a " +" so i can split the string at the spaces. How should I go about using

字符串replaceAll方法来替换这些特殊字符？下面是我的代码

the string replaceAll method to replace these special characters? Below is my code

线程main中的异常java.util.regex.PatternSyntaxException：在索引0附近悬挂元字符'+'
+
^

 public static void parse(String x){
       String z = "x^2+2=2x-1";

       String[] lrside =  z.split("=",4);
       System.out.println("Left side: " + lrside[0] + " / Right Side: " + lrside[1]);
       String rightside = lrside[0];
       String leftside = lrside[1];

       rightside.replaceAll("-", " -");
       rightside.replaceAll("+", " +");
       leftside.replaceAll("-", " -"); leftside.replaceAll("+", " +");
       List<String> rightt = Arrays.asList(rightside.split(" "));
       List<String> leftt = Arrays.asList(leftside.split(" "));

       System.out.println(leftt);
       System.out.println(rightt);

推荐答案

replaceAll 接受正则表达式作为其第一个参数。

replaceAll accepts a regular expression as its first argument.

+ 是一个特殊字符，表示一次或多次出现的量词。因此，它应该转义为指定文字字符 + ：

+ is a special character which denotes a quantifier meaning one or more occurrences. Therefore it should be escaped to specify the literal character +:

rightside = rightside.replaceAll("\\+", " +");

（字符串是不可变的，所以有必要将变量赋给 replaceAll ）;

(Strings are immutable so it is necessary to assign the variable to the result of replaceAll);

另一种方法是使用字符类，删除元字符状态：

An alternative to this is to use a character class which removes the metacharacter status:

rightside = rightside.replaceAll("[+]", " +");

最简单的解决方案是使用 replace 使用非正则表达式的方法字符串文字：

The simplest solution though would be to use the replace method which uses non-regex String literals:

rightside = rightside.replace("+", " +"); 

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