/*Java Hashtable example. This Java Hashtable example describes the basic operation performed on the hashtable.*/import java.util.Hashtable;import java.util.Enumeration;public class HashtableExample{public static void main(String args[]){// constructs a new empty hashtable with default initial capacityHashtable hashtable = new Hashtable();/* To specify initial capacity, use following constructor.燞ashtable hashtable = new Hashtable(100);燭o create hashtable from map use following constructor燞ashtable hashtable = new Hashtable(Map myMap);?/hashtable.put( "One", new Integer(1) ); // adding value into hashtablehashtable.put( "Two", new Integer(2) );hashtable.put( "Three", new Integer(3) );/*IMPORTANT : We CAN NOT add primitives to the hashtable. We have to wrap it into one of the wrapper before adding.*//*To copy all key - value pairs from Map to Hashtable use putAll method.Signature of putAll method is,void putAll(Map m)*///get number of keys present in the hashtableSystem.out.println("Hashtable contains " + hashtable.size() + " key value pair."); /*To check whether Hashtable is empty or not, use isEmpty() method.isEmpty() returns true is Hashtable is empty, otherwise false.*//*Finding particular value from the Hashtable : Hashtable's contains method returns boolean depending upon the presense of the value in given hashtableSignature of the contains method is,boolean contains(Object value)*/if( hashtable.contains( new Integer(1) ) ){System.out.println("Hashtable contains 1 as value");}else{System.out.println("Hashtable does not contain 1 as value");}/*Finding particular Key from the Hashtable : Hashtable's containsKey method returns boolean depending upon the presense of the key in given hashtableSignature of the method is,boolean containsKey(Object key)*/if( hashtable.containsKey("One") ){System.out.println("Hashtable contains One as key");}else{System.out.println("Hashtable does not contain One as value");}/*Use get method of Hashtable to get value mapped to particular key.Signature of the get method is,Object get(Object key)*/Integer one = (Integer) hashtable.get("One");System.out.println("Value mapped with key \"One\" is " + one);/*IMPORTANT:?get method returns Object, so we need to downcast it.*//*To get all keys stored in Hashtable use keys method.Signature of the keys method is,Enumeration keys()To get Set of the keys use keySet() method instead.Set keySet()*/System.out.println("Retriving all keys from the Hashtable");Enumeration e = hashtable.keys();while( e. hasMoreElements() ){System.out.println( e.nextElement() );}/*To get all values stored in Hashtable牋牋 use elements method.Signature of the elements method is,Enumeration elements()To get Set of the values use entrySet() method instead.Set entrySet()*/System.out.println("Retriving all values from the Hashtable");e = hashtable.elements();while( e. hasMoreElements() ){System.out.println( e.nextElement() );}/*To remove particular key - value pair from the Hashtable use remove method.Signature of remove methid is,Object remove(Object key)This method returns value that had mapped to the given key, otherwise null if mapping not found.*/System.out.println( hashtable.remove("One") + " is removed from the Hashtable.");}}/*OUTPUT of the above given Java Hashtable Example would be :Hashtable contains 3 key value pair.Hashtable contains 1 as valueHashtable contains One as keyValue mapped with key "One" is 1Retriving all keys from the HashtableOneThreeTwoRetriving all values from the Hashtable1321 is removed from the Hashtable.*/
是数据结构。