在java中的String replaceAll方法未提供预期的结果

Question

Following is the program which is not giving expecting result with replaceAll method.

public class HelloWorld{
     public static void main(String []args){
         String source = "Stack Overflow is a question and answer (site) for professional.";
         String txt1 = "question and answer (site) for";
        String text2 = "changed question and answer (site) for";
        source = source.replaceAll(txt1, text2);
        System.out.println(source);
     }
}

If I remove parenthesis (ie brackets) in source, text1 and text2 for a word "site" it is giving proper result. Can some one help me what would be the problem in it?

Answer 1

replaceAll method takes regular expression as arguements. And as the parentheses is a character used in regex so those are not recognized directly. you can do use Pattern.quote to get the literal string.

Answer 2

Parentheses are used for grouping. If you want them to be literal,

String txt1 = "question and answer \\(site\\) for";

This applies only to the pattern, not the replacement string.

Grouping is used in regex for accessing parts of the matched string if you use wildcards.

"abc(\\d+)def"

With this you can, after the match, determined the digits matched by the middle part.

Or you use

source = source.replace(txt1, text2);

without any regex wizardry. (It still replaces all occurrences.)

Answer 3

If you are just going to replace plain strings and are not using regular expressions at all, you don't need to change the parentheses. Instead you just let Java escape all special characters using Pattern.quote in the searched string like that:

public class HelloWorld{
     public static void main(String []args){
         String source = "Stack Overflow is a question and answer (site) for professional.";
         String txt1 = "question and answer (site) for";
        String text2 = "changed question and answer (site) for";
        source = source.replaceAll(Pattern.quote(txt1), text2);
        System.out.println(source);
     }
}