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Understanding Greedy Quantifier * and +

techbro asked
Last Modified: 2012-06-21
I ran these arguments given below:

[wow]* "wow its cool"
Output: 0 "wow" 3 "" 4 "" 5 "" 6 "" 7 "" 8 "" 9 "oo" 11 "" 12 ""

[wow]+ "wow its cool"
Output: 0 "wow" 9 "oo"

I know that * is a greedy quantifier which matches as many as it can and must be zero or more, so there are empty strings after "wow". But can you tell me the reason I got "oo" in the output for both + and *?

I find greedy quantifiers hard to understand. I know + means 1 or more, and * mean zero or more, but I am not sure under what situation I am supposed to use each of them?
Can you simplify the difference between them? (Any analogy or examples would helpful)

I used the code below to try those greedy quantifiers:

import java.util.regex.*;
public class TestClass
	public static void main(String[] args)
		Pattern p = Pattern.compile(args[0]);
		Matcher m = p.matcher(args[1]);
		boolean b = false;
		while(b = m.find())
		    System.out.print(m.start()+" \""+m.group()+"\" ");

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I will appreciate your response.
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