Difference between Arrays.asList(array) and new ArrayList<Integer>(Arrays.asList(array)) in java

Difference between Arrays.asList(array) and new ArrayList<Integer>(Arrays.asList(array)) in java

In Java, both Arrays.asList(array) and new ArrayList<Integer>(Arrays.asList(array)) are used to convert an array to a List. However, there is a subtle but significant difference between the two:

  1. Arrays.asList(array):

    • This method is a static method of the java.util.Arrays class.
    • It returns a fixed-size list backed by the original array. The returned list cannot be resized (adding or removing elements) because it is a view of the original array.
    • Any changes made to the returned list (e.g., modifying elements) will also affect the original array, and vice versa.
    • This is an efficient way to create a read-only view of the array as a list.
    • It does not create a new ArrayList object.

    Example:

    Integer[] array = {1, 2, 3}; List<Integer> list = Arrays.asList(array); list.set(0, 99); // Modifies the original array

  2. new ArrayList<Integer>(Arrays.asList(array)):

    • This code creates a new ArrayList<Integer> object and initializes it with the elements from the array obtained by Arrays.asList(array).
    • The resulting ArrayList is a completely separate object from the original array.
    • You can modify the ArrayList independently without affecting the original array, and vice versa.
    • It provides a mutable ArrayList that can be resized by adding or removing elements.

    Example:

    Integer[] array = {1, 2, 3}; List<Integer> list = new ArrayList<Integer>(Arrays.asList(array)); list.add(4); // Does not modify the original array

So, the key difference is that Arrays.asList(array) returns an immutable list view of the array, while new ArrayList<Integer>(Arrays.asList(array)) creates a new mutable ArrayList containing the elements of the array. Depending on your use case, you should choose the one that best suits your requirements.

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