Java Map equivalent in C#


Question

I'm trying to hold a list of items in a collection with a key of my choice. In Java, I would simply use Map as follows:

class Test {
  Map<Integer,String> entities;

  public String getEntity(Integer code) {
    return this.entities.get(code);
  }
}

Is there an equivalent way of doing this in C#? System.Collections.Generic.Hashset doesn't uses hash and I cannot define a custom type key System.Collections.Hashtable isn't a generic class
System.Collections.Generic.Dictionary doesn't have a get(Key) method

1
146
1/8/2013 6:33:49 AM

Accepted Answer

You can index Dictionary, you didn't need 'get'.

Dictionary<string,string> example = new Dictionary<string,string>();
...
example.Add("hello","world");
...
Console.Writeline(example["hello"]);

An efficient way to test/get values is TryGetValue (thanx to Earwicker):

if (otherExample.TryGetValue("key", out value))
{
    otherExample["key"] = value + 1;
}

With this method you can fast and exception-less get values (if present).

Resources:

Dictionary-Keys

Try Get Value

176
10/15/2014 1:26:15 PM

Dictionary<,> is the equivalent. While it doesn't have a Get(...) method, it does have an indexed property called Item which you can access in C# directly using index notation:

class Test {
  Dictionary<int,String> entities;

  public String getEntity(int code) {
    return this.entities[code];
  }
}

If you want to use a custom key type then you should consider implementing IEquatable<> and overriding Equals(object) and GetHashCode() unless the default (reference or struct) equality is sufficient for determining equality of keys. You should also make your key type immutable to prevent weird things happening if a key is mutated after it has been inserted into a dictionary (e.g. because the mutation caused its hash code to change).


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