how to find the No. of matches if i use patterns and matcher in java?

Question

i have the following code

    Pattern keyPattern = Pattern.compile(key);
    Matcher matcher = keyPattern.matcher(str);
    return matcher.replaceAll(value);

this will replaces the key in the str with value; but i want to know how many instances of key's has been replaced with value. so how to know that?

Answer 1

You can use the find method in a loop to count. There is an example in the Java tutorial:

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class MatcherDemo {

    private static final String REGEX = "\\bdog\\b";
    private static final String INPUT = "dog dog dog doggie dogg";

    public static void main(String[] args) {
       Pattern p = Pattern.compile(REGEX);
       Matcher m = p.matcher(INPUT); // get a matcher object
       int count = 0;
       while(m.find()) {
           count++;
           System.out.println("Match number "+count);
           System.out.println("start(): "+m.start());
           System.out.println("end(): "+m.end());
       }
    }
}

While you are calling find, you can at the same time collect the parts of the string and manually build the result in a StringBuffer. Or if performance is not an issue, you can first count and then afterwards scan the string again with replaceAll.

Answer 2

instead you could do:

int num = 0;
Pattern keyPattern = Pattern.compile(key);
Matcher matcher = keyPattern.matcher(str);
while(matcher.find()){
    str = matcher.replaceFirst();
    matcher = keyPattern.matcher(str); //don't know if this line is necessary
    num++;
}