Java String.split() 在元字符处 +
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String.split() at a meta character +
提问by apache
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
我正在制作一个简单的程序，该程序将处理来自方程的字符串输入的方程 但是，当我运行它时，由于尝试将“+”替换为“+”，因此我可以拆分字符串，因此出现异常在空间。我应该如何使用
the string replaceAll method to replace these special characters? Below is my code
字符串 replaceAll 方法来替换这些特殊字符？下面是我的代码
Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta character '+' near index 0 + ^
线程“main”中的异常 java.util.regex.PatternSyntaxException：在索引 0 + 附近悬空元字符 '+'
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);
采纳答案by Reimeus
replaceAllaccepts a regular expression as its first argument.
replaceAll接受一个正则表达式作为它的第一个参数。
+is a special character which denotes a quantifier meaning one or more occurrences. Therefore it should be escaped to specify the literal character +:
+是一个特殊字符，它表示一个表示一个或多个出现的量词。因此应该转义以指定文字字符+：
rightside = rightside.replaceAll("\+", " +");
(Strings are immutable so it is necessary to assign the variable to the result of replaceAll);
（字符串是不可变的，因此有必要将变量分配给replaceAll）；
An alternative to this is to use a character classwhich removes the metacharacter status:
对此的替代方法是使用删除元字符状态的字符类：
rightside = rightside.replaceAll("[+]", " +");
The simplest solution though would be to use the replacemethod which uses non-regex Stringliterals:
最简单的解决方案是使用replace使用非正则表达式String文字的方法：
rightside = rightside.replace("+", " +");
回答by Subhrajyoti Majumder
String#replaceAllexpects regexas input, and +is not proper pattern, \\+would be pattern. rightside.replaceAll("\\+", " +");
String#replaceAll期望regex作为输入，而+不是正确的模式，\\+将是模式。rightside.replaceAll("\\+", " +");
回答by Aniket Thakur
I had similar problem with regex = "?". It happens for all special characters that have some meaning in a regex. So you need to have "\\"as a prefix to your regex.
我有类似的问题regex = "?"。它发生在所有在正则表达式中具有某种意义的特殊字符上。因此，您需要将其"\\"作为正则表达式的前缀。
rightside = rightside.replaceAll("\+", " +");
