Sets differ from lists in that they are unordered and cannot contain duplicates of the same element. : Set « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. Set

import java.util.HashSet;
import java.util.Iterator;
   
public class MainClass {
 public static void main(String args[]){
    HashSet set = new HashSet();
    set.add("This");
    set.add("is");
    set.add("is");
    set.add("a");
    set.add("a");
    set.add(null);
    set.add("test");
    displaySet(set);
 }
 static void displaySet(HashSet set) {
  System.out.println("The size of the set is: "+set.size());
  Iterator i = set.iterator();
  while(i.hasNext()){
   Object o = i.next();
   if(o == null) System.out.println("null");
   else System.out.println(o.toString());
  }
 }
}