Question

Code:public class duplicate

{

public static void main(String[] args)throws IOException

  {

  System.out.println("Enter words separated by spaces ('.' to quit):");

  Set<String> s = new HashSet<String>();

  Scanner input = new Scanner(System.in);

  while (true)

  {

  String token = input.next();

  if (".".equals(token))

  break;

  if (!s.add(token))

  System.out.println("Duplicate detected: " + token);

  }

  System.out.println(s.size() + " distinct words:\n" + s);
 Set<String> duplicatesnum = new HashSet<String>();

String token = input.next();
if (!s.add(token))
{
duplicatesnum.add(token);
System.out.println(“Duplicate detected: ” + token);
}

System.out.println(duplicatesnum.size());

}
}
the output is:
Enter words separated by spaces (‘.’ to quit):
one two one two .
Duplicate detected: one
Duplicate detected: two
2 distinct words:
[two, one]

Answer 1

I assume you want to know the number of different duplicate words. You can use another HashSet<String> for the duplicates.

//Outside the loop
Set<String> duplicates = new HashSet<String>();

//Inside the loop
if (!s.add(token))
{
    duplicates.add(token);
    System.out.println("Duplicate detected: " + token);
}

//Outside the loop
System.out.println(duplicates.size());

Also if you care for the occurences of each word declare a HashMap<String, Integer> as in others posts is mentioned.

But if you want the number of all duplicate words(not different) just declare a counter:

//Outside the loop
int duplicates = 0;    

//Inside the loop
if (!s.add(token))
{
    duplicates++;
    System.out.println("Duplicate detected: " + token);
}

//Outside the loop
System.out.println(duplicates);