Java: How to convert HashMap to ArrayList?

Question

Hi in my program I was using HashMap to store some values of the type String and Object. I was hoping to convert this to an ArrayList so I wouldn't need to use a HashMap at all. Here's the snippets of my code that has HashMap in it:

private HashMap directions;

descriptions = new HashMap();

And then later, inside a method and in some if loops, I have:
directions.put("north", north);
directions.put("east", east);
directions.put("south", south);
directions.put("west", west);

And later I have:
Set keys = directions.keySet();

Is it possible to do this using an ArrayList instead?

Ratchetr · Answer

Why are you using HashMap() rather than HashMap<K,V>()?

Doesn't your IDE or compiler warn you that:

HashMap is a raw type. References to generic type HashMap<K,V> should be parameterized?

Right now, you are indexing into the hashmap using strings: north, south, etc.

For an ArrayList, you can only index by an integer, through the get method.

You can do list.get(1), but you can't do list.get("north") with an ArrayList. (You also can't do list[1], but that is just because Java is a mildly retarded language that doesn't have proper support for operator overloading).

What you can do is use an Enum:

public enum Direction { NORTH, SOUTH, EAST, WEST };

That will basically give you 4 symbolic names Direction.NORTH, Direction.SOUTH, etc. With values 0, 1 ,2 and 3. Since they are really just numbers, you can use them to index into an array:

directions.get(Direction.NORTH);

Oh...wait...that won't work. Good grief Java is just plain too pedantic sometimes.

This should work:

directions.get(Direction.NORTH.ordinal());

Gennie · Answer

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Java: How to convert HashMap to ArrayList?
Hi in my program I was using HashMap to store some values of the type String and Object. I was hoping to convert this to an ArrayList so I wouldn&#39;t need to use a HashMap at all. Here&#39;s the snippets of my code that has HashMap in it:

private HashMap directions;

descriptions = new...

Bob · Answer

The problem is that you've already stumbled upon the best solution for storing your data (a HashMap) so it's somewhat perverse to change it to an inferior structure.

I guess the underlying question is why do want to lose the HashMap?  It's a standard part of Java, it's fairly efficient and it's really useful.  So why not use it?

PS: You should use the generic version "HashMap<String, Object>() " rather than the raw version "HashMap()" which is now obsolete.

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Java: How to convert HashMap to ArrayList?

3 Answers