Using the Pattern Matcher regular expression classes

Question

In the following example:

class ZiggyTest2{  
        public static void main(String[] args){  

            Pattern p = Pattern.compile("Water water WATER everywhere");
            Matcher m = p.matcher("water");

            while(m.find()){
                System.out.println(m.start() + " " + m.group());
            }

            System.out.println("[Done]");
        }    
    }  

The m.find() method is always false so it is not finding the string "water". What is the reason for this?

Answer 1

You have inverted the strings:

• Pattern compiles the regex,
• Matcher applies on an input.

You should have:

        Pattern p = Pattern.compile("water");
        Matcher m = p.matcher("Water water WATER everywhere");

Also note that if you want case insensitive matching, you want to initialize your pattern with either of:

        Pattern p = Pattern.compile("water", Pattern.CASE_INSENSITIVE);
        // or:
        Pattern p = Pattern.compile("(?i)water");