Zero-width RegEx does not match in Java

I am studying the zero-width RegEx. First, I test my pattern and text at http://testregex.com/ and it works well. Then I test them in my Java program, but they don't match. So I'd like to make it clear the cause of problem. Any reply would be appreciated. Thanks!

pattern:`\w*(?=ing)`

text:I’m singing while you’re dancing

Java code:

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


public class RegexDemo {

  public static void main(String[] args) {
    RegexDemo demo = new RegexDemo();
    System.out.printf("%b%n", demo.zeroWidthAssertionEarly());
  }

  public boolean zeroWidthAssertionEarly()  
  {  
    String reg="\\w*(?=ing)";
    String word = "I’m singing while you’re dancing";
    boolean tem=false;  

    Pattern pattern = Pattern.compile(reg);  
    Matcher matcher = pattern.matcher(word);  

    tem = matcher.matches(); 

    return tem;  
  } 
}

Thank you in advance. Now I hope I do better understand the difference between match() and find(), and I modified my code as follows:

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

public class RegexDemo {
  public static void main(String[] args) {
    RegexDemo demo = new RegexDemo();
    System.out.printf("%b%n", demo.zeroWidthAssertionEarly());
  }

  public boolean zeroWidthAssertionEarly()  
  {  
    //匹配以ing结尾的单词
    String reg="\\w*(?=ing)";
    String word = "I’m singing while you’re dancing";//
    boolean tem=false;  

    Pattern pattern = Pattern.compile(reg);  
    Matcher matcher = pattern.matcher(word);  

    while(matcher.find()){
      System.out.printf("start = %d%n", matcher.start());
      System.out.printf("end = %d%n", matcher.end());
    }        
    return tem;  
  } 
}

Its output confused me:

start = 4
end = 8
start = 8
end = 8
start = 25
end = 29
start = 29
end = 29
false

So my new question is: Why the output is not as follows?

start = 4
end = 8
start = 25
end = 29
false