How to match duplicate words in a regular expression using Java

Problem Description

How to match duplicate words in a regular expression?

Solution

Following example shows how to search duplicate words in a regular expression by using p.matcher() method and m.group() method of regex.Matcher class.

import java.util.Scanner;
import java.io.*;
import java.util.regex.*;
import java.util.ArrayList;

public class dupl {
   public static void main(String[] args) {
      ArrayList <String> manyLines = new ArrayList<String>();
      ArrayList <String> noRepeat = new ArrayList<String>(); 
      try { 
         String s1 = "Hello hello Hello there there past pastures ";
         Scanner myfis = new Scanner(s1);
         while(myfis.hasNext()) { 
            String line = myfis.nextLine();
            String delim = System.getProperty("line.separator");
            String [] lines = line.split(delim);
            
            for(String s: lines) { 
               if(!s.isEmpty() && s != null) { 
                  manyLines.add(s);
               } 
            } 
         }
         if(!manyLines.isEmpty()) { 
            System.out.print("Original text is:\n");
            for(String s: manyLines) { 
               System.out.println(s);
            } 
         } 
         if(!manyLines.isEmpty()) { 
            for(String s: manyLines) { 
               String result = s.replaceAll("(?i)\\b([a-z]+)\\b(?:\\s+\\1\\b)+", "$1");
               noRepeat.add(result);
            } 
         } 
         if(!noRepeat.isEmpty()) { 
            System.out.print("After Remove duplicates:\n");
            for(String s: noRepeat) { 
               System.out.println(s);
            } 
         } 
      } catch(Exception ex) { 
         System.out.println(ex);
      } 
   }
}

Result

The above code sample will produce the following result.

Original text is:
Hello hello Hello there there past pastures 
After Remove duplicates:
Hello there past pastures