What is the difference between ArrayList.clear() and ArrayList.removeAll() in java?

What is the difference between ArrayList.clear() and ArrayList.removeAll() in java?

In Java, ArrayList.clear() and ArrayList.removeAll(Collection<?> c) are two different methods provided by the ArrayList class for removing elements from an ArrayList. They serve different purposes and have distinct behaviors:

  1. ArrayList.clear():

    • The clear() method is used to remove all elements from the ArrayList, effectively making it an empty list.
    • It does not take any arguments and does not require you to specify which elements to remove.
    • After calling clear(), the ArrayList will be empty, but it will still retain its capacity (the underlying array's size will not be changed).

    Example:

    ArrayList<String> list = new ArrayList<>(); list.add("apple"); list.add("banana"); list.clear(); // Removes all elements, list is now empty

  2. ArrayList.removeAll(Collection<?> c):

    • The removeAll(Collection<?> c) method is used to remove all elements from the ArrayList that are also present in the specified collection c.
    • It takes a collection as an argument and removes elements from the list that are found in both the ArrayList and the specified collection c.
    • After calling removeAll(), the ArrayList will contain only elements that are not in the specified collection c.

    Example:

    ArrayList<String> list = new ArrayList<>(); list.add("apple"); list.add("banana"); list.add("cherry"); ArrayList<String> toRemove = new ArrayList<>(); toRemove.add("banana"); toRemove.add("cherry"); list.removeAll(toRemove); // Removes "banana" and "cherry" from the list

In summary:

  • clear() removes all elements from the ArrayList without considering any specific criteria. It empties the list.
  • removeAll(Collection<?> c) removes elements from the ArrayList that are also present in the specified collection. It is used for selective removal based on the elements in the provided collection.

Choose the method that fits your specific use case. If you need to remove all elements, use clear(). If you want to remove specific elements based on a criterion or another collection, use removeAll(Collection<?> c).

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