Emptying an ArrayList in Java

Question

I have an ArrayList:

ArrayList<OrderItem> orderItems = new ArrayList<OrderItem>();

It is filled with objects. I want to press a button that would effectively delete all the objects in this list. How can I do this?

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score 4 · Answer 1 · edited May 23 '17 at 12:08

4

Use clear() method

 orderItems.clear();

And

The main thing to be concerned about is what other code might have a reference to the list.

Prefer to read @Skeets answer : Better practice to re-instantiate a List or invoke clear()

edited May 23 '17 at 12:08

Community

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answered Jul 24 '13 at 12:17

Suresh Atta

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score 3 · Answer 2 · answered Jul 24 '13 at 12:17

3

Use clear() method like this orderItems.clear()
It Removes all of the elements from this list. The list will be empty after this call returns.

answered Jul 24 '13 at 12:17

Prabhaker A

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AllTooSir · Answer 3 · 2013-07-24T12:22:39.503

3

You can use ArrayList#clear() .

Removes all of the elements from this list. The list will be empty after this call returns.

With clear() , you don't need to create a new ArrayList object . It just empties the ArrayList.

orderItems.clear();
orderItems.trimToSize();

edited Jul 24 '13 at 12:22

answered Jul 24 '13 at 12:17

AllTooSir

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score 1 · Answer 4 · answered Jul 24 '13 at 12:20

Collection interface itself defines a void clear(); method.

/**
 * Removes all of the elements from this collection (optional operation).
 * The collection will be empty after this method returns.
 *
 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
 *         is not supported by this collection
 */

In your buttons actionListner just use orderItems.clear();. This will remove all elements of that Collection(ArrayList in your case).

    myButton.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            orderItems.clear();

        }
    });

Adrian Jandl · Answer 5 · 2013-07-24T12:30:50.843

0

Add an ActionListener to your button where you set

orderItems = new ArrayList();

That would delete every item in the list.

edited Jul 24 '13 at 12:30

answered Jul 24 '13 at 12:16

Adrian Jandl

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That's a new variable with the same name --> would not compile. – jlordo Jul 24 '13 at 12:18
@jlordo it would definitely compile, but you'd shadow the orderItems field and not much would happen at all. – kritzikratzi Jul 24 '13 at 12:26
@kritzikratzi: that's correct. – jlordo Jul 24 '13 at 12:28
@jlordo Edited. Don't know how that happened. – Adrian Jandl Jul 24 '13 at 12:32
@AdrianJandl: revoked my downvote, even though it is still not precise. This won't delete any item out of a list, it creates a new list and assigns it to the variable. If the other list isn't referenced any more, it is eligible for garbage collection. – jlordo Jul 24 '13 at 12:33
@jlordo You're right. Though it depends on what the OP means by "delete". It will provide him with an empty ArrayList. – Adrian Jandl Jul 24 '13 at 12:35

score 0 · Answer 6 · answered Jul 24 '13 at 12:20

0

There is one inbuilt method in ArrayList.So you can implement it on orderdItems like:

orderedItems.clear()

Also check this: http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html

answered Jul 24 '13 at 12:20

Manish Doshi

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score 0 · Answer 7 · answered Jul 24 '13 at 12:20

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You can empty the ArrayList by calling the clear method

orderItems.clear();

answered Jul 24 '13 at 12:20

Prabhakaran Ramaswamy

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Emptying an ArrayList in Java

7 Answers7