Java 集合大小

import java.util.*;

public class CollectionTest {
   public static void main(String [] args) {   
      System.out.println( "Collection Example!\n" );
      int size;
      HashSet <String>collection = new HashSet <String>();
      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("Collection data: ");  
      iterator = collection.iterator();     

      while (iterator.hasNext()) {
         System.out.print(iterator.next() + " ");  
      }
      System.out.println();
      size = collection.size();

      if (collection.isEmpty()) {
         System.out.println("Collection is empty");
      } else {
         System.out.println( "Collection size: " + size);
      }
      System.out.println();
   }
}