Question

Consider this code:

import java.util.regex.*;

public class Pattern3 {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here

        Pattern p = Pattern.compile("Our"); //line 1
        Matcher m = p.matcher("Our mom and Our dad"); //line 2

        //p.compile(mom); commented line

         StringBuffer s = new StringBuffer();



       boolean found = m.find();

        while (found){
            m.appendReplacement(s, "My"); //line 3
            found=m.find();
        }

       m.appendTail(s); //line 4
       System.out.println(s);
    }

}

a) Why do I need to call m.appendTrail(s) on line 4 to get the unchopped string?

b) Why doesn’t the output change when I uncomment and place "mom" as the new regex expression?

Answer 1

Just read the documentation for

Matcher.appendReplacement and

Matcher.appendTail

It’s all explained there what is the intention on using these two methods together.

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Changing the pattern after having created an instance of a matcher of course won’t influence the already created matcher. You have to change the pattern before you create the matcher.