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7.
8. hash.put("Jiangsu","Nanjing");
9. //将字符串对象“Jiangsu”给定一关键字“Nanjing”,并将它加入hash
10.hash.put("Beijing","Beijing");
11.hash.put("Zhejiang","Hangzhou");
12.
13.System.out.println("The hashtable hash1 is: "+hash);
14.System.out.println("The size of this hash table is "+hash.size());
15.//打印hash的内容和大小
16.
17.Enumeration enum1=hash.elements();
18.System.out.print("The element of hash is: ");
19.while(enum1.hasMoreElements())
20.System.out.print(enum1.nextElement()+" ");
21.System.out.println();
22.//依次打印hash中的内容
23.if(hash.containsKey("Jiangsu"))
24.System.out.println("The capatial of Jiangsu is "+hash.get("Jiangsu"));
25.hash.remove("Beijing");
26.//删除关键字Beijing对应对象
27.System.out.println("The hashtable hash2 is: "+hash);
28.System.out.println("The size of this hash table is "+hash.size());
29.}
30.}
31.
32.运行结果：
33.The hashtable hash1 is: {Beijing=Beijing, Zhejiang=Hangzhou, Jiangsu=Nanjing}
34.The size of this hash table is 3
35.The element of hash is: Beijing Hangzhou Nanjing
36.The capatial of Jiangsu is Nanjing
37.The hashtable hash2 is: {Zhejiang=Hangzhou, Jiangsu=Nanjing}
38.The size of this hash table is 2
Hashtable是Dictionary(字典)类的子类。在字典类中就把关键字对应到数据值。字典类是一个抽象类。在java.util中还有一个类Properties，它是Hashtable的子类。用它可以进行与对象属性相关的操作。
1.8 位集合类BitSet
位集合类中封装了有关一组二进制数据的操作。
我们先来看一下例8.6 BitSetApp.java。