ArrayLists and indexers in Java

Question

Is it possible to do this in Java? Maybe I'm using the wrong syntax?

ArrayList<Integer> iAL = new ArrayList<Integer>();
iAL.addAll(Arrays.asList(new Integer[] {1, 2, 3, 4, 5 }));

for (int i = 0; i < iAL.size(); ++i) {
    System.out.println(iAL[i]); //<-------- HERE IS THE PROBLEM
}

Also, is it possible to do something like

iAL.addAll( new int[] {1, 2, 3, 4, 5} );

as is seen on c#?

Thanks

Answer 1

Try System.out.println(iAL.get(i));. Because it's a List, not array

Answer 2

ArrayList<Integer> iAL = new ArrayList<Integer>();
iAL.addAll(Arrays.asList(new Integer[] {1, 2, 3, 4, 5 }));

for (int i = 0; i < iAL.size(); ++i) {
    System.out.println(iAL.get(i)); 
}

AFAIK

iAL.addAll(Arrays.asList(new Integer[] {1, 2, 3, 4, 5 })); // this is the shortest solution

Answer 3

In addition, I would add two other notes about your code:

• You may find the for-each syntax appealing.
  
• Consider the advantages of coding to the interface.

For example, combining several helpful suggestions from other answers

List<Integer> list = new ArrayList<Integer>();
list.addAll(Arrays.asList(1, 2, 3, 4, 5 ));

for (Integer i : list) {
    System.out.println(i);
}

Addendum: The question of coding to the interface is interesting, and Carl's comment is particularly apropos. Using the interface type, List, minimizes your obligation to use a specific implementation. If the need arises, you can later switch to any class that implements List.

Answer 4

Also, is it possible to do something like

iAL.addAll( new int[] {1, 2, 3, 4, 5} );

Close enough:

iAL.addAll(Arrays.asList(1, 2, 3, 4, 5));

No need for the new Integer[] in your code.

Answer 5

No, you must use .get(i); [i] is for arrays only. However, if you don't need the index variable for something else, the for-each syntax is preferable (as per trashgod's answer).

For the second, if you aren't resizing the List (it is still fine to mutate individual elements), it would be perfectly reasonable to do the following:

List<Integer> iAL = Arrays.asList(1, 2, 3, 4, 5);

Note, that Arrays.asList() accepts a varargs parameter, so no reason to explicitly construct the array.

If you want a resizable List, the following is probably the shortest:

List<Integer> iAL = new ArrayList<Integer>(Arrays.asList(1, 2, 3, 4, 5));

Answer 6

I will refactor your entire code to :

List<Integer> iAL = Arrays.asList(1, 2, 3, 4, 5 );

for (int i : iAL) {
  System.out.println(i);
}