CODEWITHSUNDEEP
java
Shile
Shile

Reputation: 33

Arbitrary number of lists within a list java

Is there a way I can add an arbitrary number of lists within a list in java?

For example:

List<List<T>, List<T>, List<T>>

I know this is incorrect syntax, but I want to do something like that.

Upvotes: 1

Views: 272

Answers (3)

tobias_k
tobias_k

Reputation: 82919

In case you meant arbitrarily nested lists of lists of lists of lists... you might want to use a tree structure instead, something like this:

class Tree<T> {
    T element;
    List<Tree<T>> children;
}

Or this, if you want to separate intermediate layers and values:

interface Tree<T> { 
}

class TreeNode<T> implements Tree<T> {
    List<Tree<T>> children;
}

class TreeLeaf<T> implements Tree<T> {
    T element;
}

Upvotes: 1

Jon Newmuis
Jon Newmuis

Reputation: 26512

Assuming you have lists list1, list2, ..., listN, there are multiple ways you could go about this:

Create your own class for a n-tuple: This methodology will allow you to limit your tuple to a specific size, without having to re-implement the methods of the Collection or List classes.

public class ThreeTuple<A, B, C> {
    private final A first;
    private final B second;
    private final C third;

    public ThreeTuple(A first, B second, C third) {
        this.first = first;
        this.second = second;
        this.third = third;
    }

    public A getFirst() {
        return first;
    }

    public B getSecond() {
        return second;
    }

    public C getThird() {
        return third;
    }
}

public class OtherClass {
    public static void main(String[] args) {
        new ThreeTuple(list1, list2, list3);
    }
}

Add n lists to a list: This methodology is definitely the simplest, but does not bound the list.

List<List<T>> lists = new ArrayList<T>();
lists.add(list1);
lists.add(list2);
lists.add(list3);

Upvotes: 0

Roddy of the Frozen Peas
Roddy of the Frozen Peas

Reputation: 15189

List<List<T>> will hold any number of List<T>. For example:

List<List<T>> listOfLists = new ArrayList<List<T>>();

for (int i = 0; i < 10; i++) { // 10 is arbitrary here; just an example
    listOfLists.add(new ArrayList<T>());
}

Without being more information about use cases or why you'd want to do this, I can't be more specific.

Upvotes: 6

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