使用 Collections 类 的collection.add() 来添加数据并使用 collection.size()来计算集合的长度

完整代码

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();}
}

结果输出

集合实例!集合数据: White Yellow Blue Green 
集合长度: 4