how to use addall() method of collections?

Question

i need to use it to merge two ordered list of objects.

Answer 1

From the API:

addAll(Collection<? extends E> c): Adds all of the elements in the specified collection to this collection (optional operation).

Here's an example using List, which is an ordered collection:

    List<Integer> nums1 = Arrays.asList(1,2,-1);
    List<Integer> nums2 = Arrays.asList(4,5,6);

    List<Integer> allNums = new ArrayList<Integer>();
    allNums.addAll(nums1);
    allNums.addAll(nums2);
    System.out.println(allNums);
    // prints "[1, 2, -1, 4, 5, 6]"

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On int[] vs Integer[]

While int is autoboxable to Integer, an int[] is NOT "autoboxable" to Integer[].

Thus, you get the following behaviors:

    List<Integer> nums = Arrays.asList(1,2,3);
    int[] arr = { 1, 2, 3 };
    List<int[]> arrs = Arrays.asList(arr);

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