CODEWITHSUNDEEP
javagethashtable
user2987516
user2987516

Reputation:

Does Hashtable get method returns more than one value?

I was converting some code from java to C#, I encountered ArrayList<Integer> values = hashtable.get(h);. Question aroused Does Hashtable get method returns more than one value?

Upvotes: 0

Views: 566

Answers (5)

mvieghofer
mvieghofer

Reputation: 2896

It does only return a list of values if you put that list in the map (under the certain key). 

Map<String, List<Object>> map = new HashMap<>();
... // init map
List<Object> list = map.get(KEY);

but

Map<String, Object> map = new HashMap<>();
map.put(KEY, obj1);
map.put(KEY, obj2);
Object obj = map.get(KEY);

Upvotes: 0

Areo
Areo

Reputation: 938

If you wold like to have many values for one key use Guava => Multimap Documentation: http://guava-libraries.googlecode.com/svn-history/r13/trunk/javadoc/com/google/common/collect/Multimap.html

Upvotes: 0

Suresh Atta
Suresh Atta

Reputation: 122018

The return type of get() method is Object. So it is a single Object. But the type can be a List or Any Class in Java.

So the returning Object purely depends on What you inserted before.

Upvotes: 0

JoeC
JoeC

Reputation: 1850

An ArrayList is one value (an arraylist) by itself

HashTable<something, ArrayList<Integer>> hashtable = new HashTable<something, ArrayList<Integer>>();

So it's gonna map the "something" to an arraylist of integers (i.e. a list)

Upvotes: 0

christopher
christopher

Reputation: 27346

A HashTable returns one value. If that value happens to be an object of type Collection, then that one value will point to several other values.

For example 

HashTable<String, ArrayList<Integer>> table = new HashTable<String, ArrayList<Integer>>();

// Populate it with values.

ArrayList<Integer> value = table.get("KEY");

How is this possible?

Simple. Java Generics. This is where you declare a Generic type in a class, and you define it's type at run time. For example:

public class Test<T>
{
      private T instance;

      public Test(T instance)
      {
          this.instance = instance;
      }
}

That means you can declare this class any way you want.

Test<String> test = new Test<String>();
Test<Integer> test2 = new Test<Integer>();

And the type of instance will be whatever you declare it as.

And because T defaults to type Object, you can even put a Collection in there.

Test<ArrayList<String>> test3 = new Test<ArrayList<String>>();

Upvotes: 1

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