Java HashMap vs. C# Hashtable

One of the things I have found has been more frustrating while picking up C# .NET for the World Wind project is that some of the simple basic programming constructs that are automatic for me in Java don't seem to be directly parallel in C#. On top of that the online documentation at the MSDN site and other places is either not intuitive or I am looking in the wrong areas.

One of the basic data structures I depend on in Java are Maps. One of the simple classes that implement the Map interface in Java is java.util.HashMap.

Like other data structure objects in Java, there is no special syntax to interact with this object, it has methods like other objects where you pass in arguments and get return values.

The most basic usage of the HashMap generally goes like this:

//construct the new map
HashMap javaMap = new HashMap();
//enter a new key value pair
javaMap.put("key","value");
//to get the all values out of the map
Set keys = javaMap.keySet();
Iterator keyIter = keys.iterator();
while(keyIter.hasNext()){
String key = (String) keyIter.next();
String value = (String) javaMap.get(key);
System.out.println(key+" = "+value);
}

So it is pretty straightforward usage (in my mind), the put method "puts" data into the Map and the "get" method retrieves data from the Map given a key. Great

C# on the other hand uses a more elaborate syntax and combination of properties, keywords and methods. Not that this is more difficult but it took some time for me to figure out for example, that there was no equivalent to the "get" method in Hashtable, that you needed to use the "[]" syntax as if this were like an array

For the equivalent C# as the above, you can use the System.Collections.Hashtable class which implements the IDictionary interface:

//construct the Hashtable
Hashtable cSharpTable = new Hashtable();
//enter new key value pairs
cSharpTable.Add("key", "value");
cSharpTable.Add("hello", "world");
//for all Keys, a public property on Hashtable class, print out the key and value
foreach (String key in cSharpTable.Keys)
{
String value = (String) cSharpTable[key];
System.Console.WriteLine(key + " = " + value);
}

So in some ways the C# code is definitely more concise. But for a Java programmer it feels a bit strange, instead of 3 methods in Java(all with clear Javadoc descriptions of use, IDE auto-complete and tool tips, same syntax as all other method calls in Java etc..) for put(),get(),keySet(), C# requires you to use three different language features, a method, Add(), a property on the object Keys (why not just use a method?), and a [] operator. Granted in Visual Studio 2005 typing "cSharpTable." and you would see a list of the public methods and properties including the Add() and Keys, but you would only see the auto-assist tool-tip if you knew to type "cSharpTable[" and then it would give you the basic description of the syntax "object Hashtable[object key]".

I guess it is just something I'll have to learn.

I basically learned Java on the fly on my first job. I learned it fairly easily because once you got it that everything is just a method its pretty easy to find and locate what you need, plus the clear and standardized format of Javadoc based sites makes learning new classes or finding methods fairly simple. Try comparing the ease of use of Sun's Java API site with Microsoft's MSDN .NET Framework Reference(see link to HashMap and Hashtable classes above). Is it really an apples to oranges comparison? Or is the MSDN site just not very readable (for that one class there is no list of methods, just pages of examples in multiple languages.

References:
Holzner, Steven Microsoft Visual C# .NET 2003 Kick Start. Indianapolis: Sams Publishing, 2004. pp243-245