Question

I’m trying to set up a constructor where a the data structure used will be determined by a string in the parameter::

DictionaryI<IPAddress,String> ipD; //declaring main structure using interface

 // Constructor, the type of dictionary to use (hash, linkedlist, array)
 // and the initial size of the supporting dictionary
    public IPManager(String dictionaryType, int initialSize){
        if(st1.equals(dictionaryType))
            ipD = new LinkedListDictionary();
        if(st2.equals(dictionaryType))
            ipD = new HashDictionary(initialSize);
        if(st3.equals(dictionaryType))
            ipD = new ArrayDictionary(initialSize);
        else
            throw new UnsupportedOperationException();
    }

when running the code I get “UnsuportedOperationException” no matter what I put in. Any help or a point in the right direction would be greatly appreciated! (Code is in Java)

Answer 1

The obvious answer is

public IPManager(String dictionaryType, int initialSize){
    if(st1.equals(dictionaryType))
        ipD = new LinkedListDictionary();
    else if(st2.equals(dictionaryType))
        ipD = new HashDictionary(initialSize);
    else if(st3.equals(dictionaryType))
        ipD = new ArrayDictionary(initialSize);
    else
        throw new UnsupportedOperationException();
}

For st1 and st2 your code would fall through to the throw.

That said, this approach is generally bad. For reference look at the Java collection interfaces (Map<K,V> for instance) and its implementations (HashMap, TreeMap, etc).