import java.util.*;

public class Main {
   public static void main(String [] args) {   
      System.out.println( "集合实例!\n" ); 
      int size;
      HashSet collection = new HashSet ();
      String str1 = "Yellow", str2 = "White", str3 = 
      "Green", str4 = "Blue";  
      Iterator iterator;
      collection.add(str1);    
      collection.add(str2);   
      collection.add(str3);   
      collection.add(str4);
      System.out.print("集合数据: ");  
      iterator = collection.iterator();     
      while (iterator.hasNext()){
         System.out.print(iterator.next() + " ");  
      }
      System.out.println();
      size = collection.size();
      if (collection.isEmpty()){
         System.out.println("集合是空的");
      }
      else{
         System.out.println( "集合长度: " + size);
      }
      System.out.println();
   }
}

集合实例!

集合数据: White Yellow Blue Green 
集合长度: 4