CODEWITHSUNDEEP
java
Iron
Iron

Reputation: 49

How to initiate multidimensional arraylist with different objects?

I'm having trouble trying to initiate an arraylist in which the first column I want to be a string, and the second column be a custom object.

For example column [0] be String, and column[1] be an Integer. Convention attempts of creating a multidimensional arraylist as in those used by int[][] or String[][] don't seem to work :( I would welcome any help. At this point I don't think it's something java allows. I can make it work for just one type of object but it's not what I want. Thanks!

Upvotes: 1

Views: 292

Answers (4)

hd1
hd1

Reputation: 34677

Sure it does, but you weaken/eliminate type-checking:

Map myMap<String>, Integer> myData = new HashMap<String, Integer>();

Now your list of strings can be retrieved by myMap.keySet() and values can be retrieved by myMap.values(). Each of these return a Set, which you can easily convert to a List using the following code:

List<String> strings = new ArrayList<String>(myMap.keySet()); // get your strings
List<Integer> numbers = new ArrayList<Integer>(myMap.values(); // get your numbers

Good luck and if you should run into problems, do leave a comment.

Upvotes: 1

Makoto
Makoto

Reputation: 106450

Arrays are geared towards one specific type of thing - be they Object or String or int. Despite the fact that you're adding multiple dimensions to them, they still only hold one type of information.

What you would rather have is a mapping between two objects. This allows you to do the following:

  • Associate any key to a particular value
  • Eliminate duplicate key entries
  • Be much easier to access instead of array indexing

Here's an example. Say your custom object is a Cat, and you want to map the name of the owner to a particular Cat. You create a new instance of a Map.

Map<String, Cat> catOwners = new HashMap<>();

You can then put elements into it...

catOwners.put("Jamie", new Cat("Tycho"));

...and retrieve them with relative ease.

Cat currentCat = catOwners.get("Jamie"); // gets Jamie's cat

if you really want to, you can even iterate over them using the Map.Entry object provided with all Maps:

for(Map.Entry<String, Cat> element : catOwners.entrySet()) {
    System.out.println(element.getKey()
        + " owns " + element.getValue().getName());
}

Upvotes: 1

jh314
jh314

Reputation: 27802

What you can do is use the generic Object type, and cast accordingly.

Upvotes: 0

user745733
user745733

Reputation:

Do you need an arraylist? You could create a Map<String, Object> or Map<String, Integer> or whatever you need..

Upvotes: 2

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