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
the string replaceAll method to replace these special characters? Below is my code
Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta character '+' near index 0 + ^
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);
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.replaceAll
accepts a regular expression as its first argument.+
is a special character which denotes a quantifier meaning one or more occurrences. Therefore it should be escaped to specify the literal character+
:(Strings are immutable so it is necessary to assign the variable to the result of
replaceAll
);An alternative to this is to use a character class which removes the metacharacter status:
The simplest solution though would be to use the
replace
method which uses non-regexString
literals:String#replaceAll
expectsregex
as input, and+
is not proper pattern,\\+
would be pattern.rightside.replaceAll("\\+", " +");