Java Generics Question

Question

How can I implement generics in this program so I do not have to cast to String in this line:

String d = (String) h.get ("Dave"); import java.util.*; public class TestHashTable { public static void main (String[] argv) { Hashtable h = new Hashtable (); // Insert a string and a key. h.put ("Ali", "Anorexic Ali"); h.put ("Bill", "Bulimic Bill"); h.put ("Chen", "Cadaverous Chen"); h.put ("Dave", "Dyspeptic Dave"); String d = (String) h.get ("Dave"); System.out.println (d); // Prints "Dyspeptic Dave" } }

cletus · Accepted Answer · 2010-02-23 05:54:33Z

You could use a Hashtable but its use is discouraged in favour of Map and HashMap:

public static void main (String[] argv) { Map<String, String> h = new HashMap<String, String>(); // Insert a string and a key. h.put("Ali", "Anorexic Ali"); h.put("Bill", "Bulimic Bill"); h.put("Chen", "Cadaverous Chen"); h.put("Dave", "Dyspeptic Dave"); String d = h.get("Dave"); System.out.println (d); // Prints "Dyspeptic Dave" }

You could replace the declaration with:

Map<String, String> h = new Hashtable<String, String>();

In general you want to use interfaces for your variable declarations, parameter declarations and return types over concrete classes if that's an option.

+1 for recommending use of interfaces for variable declarations, and return types where feasibile
Use Collections.synchronizedMap( new HashMap<...> () ) instead of hashtable.

Cornelius Dol · Accepted Answer · 2010-02-23 08:05:53Z

1

Hashtable<String,String> h = new Hashtable<String,String>();

edited Feb 23, 2010 at 8:05

answered Feb 23, 2010 at 5:54

Cornelius Dol

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2 Comments

polygenelubricants Over a year ago

Hashtable is genericized as Hashtable<K, V>. java.sun.com/javase/6/docs/api/java/util/Hashtable.html

cletus Over a year ago

While I recommend using Map as the type this answer is technically correct so +1 to cancel out a somewhat overzealous downvote.

Luhar · Accepted Answer · 2010-02-23 10:15:03Z

You could also use a ConcurrentHashMap, which like HashTable is Thread safe, but you can also use the 'generic' or parameterized form.

 Map<String, String> myMap = new ConcurrentHashMap<String,String>();

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