Using LinkedList Java Class

Question

I am am trying to use the LinkedList class to load an array of anything. I was looking at the documentation of addAll method and it seem to me that I could load an array of stuff with very little effort.

addAll(int index, Collection<? extends E> c) 
      Inserts all of the elements in the specified collection into this list,
      starting at the specified position.

But I am not so sure on how to structure it.

Let's just say I have an array of Objects and I am trying to load the objects into a link list.
How would I write this?

NOTE: I am trying to load it to a list because I will be deleting and adding at multiple times.

I used below code but I get an error:

    int[] a = new int[5];
    for(int index = 0; index<5; index++){
        a[index] = index;

    }

    List<Integer> list = new LinkedList<Integer>();
    list.addAll(Arrays.asList(a)); //error Here won't take a[]

I went with an ArrayList but I am itching to know why this is not working??? — Tags
– Tags, Commented Dec 11, 2011 at 9:55

Premraj · Accepted Answer · 2011-12-25 07:07:50Z

2

If you need specifically LinkedList or mutable collection class (you mentioned add/delete operations) then Arrays.asList(T...) won't help as it returns a fixed-size list backed by the specified array and hence not mutable and Arrays.asList(T...).add(T) call will always fail.

If you don't need an array, use collection classes from start only(like ArrayList or LinkedList). In case if it's not possible this collection tutorial will give you fair idea about usage and other aspects.

if you wanto to create an ArrayList (or LinkedList) you can use (and it will copy all the elements of an array to List)-

new ArrayList<Element>(Arrays.asList(array))

EDIT -

If the array itself is a primitive array (which you shown in example) then above approach will not work either because Arrays.asList(int[]) will actually return single element List<int[]> and that's why you're getting error in your example.
If you find yourself working heavily with collection of primitives then I would suggest to look at Trove or may be Guava which provides awesome utilities pertaining to collections and other day to day needs(it has Ints.asList() method which satisfy your requirement, see doc).

edited Dec 25, 2011 at 7:07

answered Dec 11, 2011 at 9:10

Premraj

7,9208 gold badges47 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Tags Over a year ago

I understand what you are saying and thank you for your help. Its just that my team mates decided to use Arrays for the project(I didnt agree). I will be removing and adding objects because the list will be increasing and decreasing randomly. But I need to get their array in to my list.

Premraj Over a year ago

@Henry then new ArrayList<Element>(Arrays.asList(array)) is a way to go :)

Tags Over a year ago

Thank you Premraj, I will go with an ArrayList. It does make sense and it will do what I need.

JB Nizet · Accepted Answer · 2011-12-11 09:14:54Z

1

Start by transforming the array into a list, and then add all the elements of this list to your linked list:

List<Foo> list = new LinkedList<Foo>();
list.addAll(Arrays.asList(myArray());

Or just iterate through the array yourself, and add every element:

List<Foo> list = new LinkedList<Foo>();
for (Foo foo : myArray) {
    list.add(foo);
}

which requires just one more line of code, is straightforward, and more efficient.

Note that ArrayList is more efficient than LinkedList in most situations.

answered Dec 11, 2011 at 9:14

JB Nizet

694k94 gold badges1.3k silver badges1.3k bronze badges

Comments

Dino · Accepted Answer · 2011-12-11 08:45:48Z

0

You can use the java.util.Arrays class:

List<MyType> list = Arrays.asList(array);

answered Dec 11, 2011 at 8:45

Dino

1,58612 silver badges12 bronze badges

5 Comments

Spoike Over a year ago

...or the OP could've used ArrayList<Object> instead of an array.

Tags Over a year ago

This only adds the instance of the array to the list not the content of the array.

Tags Over a year ago

I cant do anything on the array side. This project is being done individually by people. I want a list because I dont have to shift or worry about dead spots(nulls).

JB Nizet Over a year ago

@Henry: Arrays.asList transforms the array into a list backed by this array. But you won't be able to add or remove alements from the returned list.

Artem Over a year ago

Henry, you should not do this if you want to modify resulting List! Arrays.asList() returns not a regular List implementation(ArrayList or LinkedList from java.util package), but unmodifiable static ArrayList class from java.util.Arrays. You should use new ArrayList<MyType>(Arrays.asList(array)) in this situation.

Collectives™ on Stack Overflow

Using LinkedList Java Class

3 Answers 3

3 Comments

Comments

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related