In this post, we will explore different ways to remove a slice from a list in Java between two specified indexes, using both built-in methods and custom logic. We will also compare the performance and trade-offs of each approach.

1. Using clear() and subList() methods

One of the simplest and most efficient ways to remove a slice from a list in Java is to use the subList() and clear() methods. The List interface provides a clear() method that removes all elements from the list. We can use it with the subList() method (that returns a view of a portion of the original list) to remove a range of elements from a list, as follows:

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The advantage of this approach is that it is very fast and concise. It does not create a new list object or copy any elements. It simply modifies the original list by removing the references to the sliced elements.

2. Using removeAll() and subList() method

Another way to remove a slice from a list in Java is to use the removeAll() method that removes all elements in the list that are contained in the specified collection. We can pass a sublist returned by the subList() method to remove elements between specified indexes. However, this works only if list contains all distinct elements.

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The advantage of this approach is that it is very fast and concise. It does not create a new list object or copy any elements. It simply modifies the original list by removing the references to the sliced elements.

3. Using Custom Logic

We can also write custom logic to iterate over the list and remove the elements that match our criteria. The idea is to move backwards in the list using a for-loop and remove all elements from the specified range. It is important to move backward in the list and not forward, since moving forward might skip a few elements in the list, leading to undesired results. For example, to remove the elements from index 1 to 3 (inclusive), we can do:

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The advantage of this approach is that it gives us more control and flexibility over the logic and criteria of removing the slice. However, it may be more verbose and error-prone than using built-in methods, and it may offer poor performance depending on the type of list and the size of the slice.

For example, for an ArrayList, this approach will also shift all the elements after the slice to the left by one position after each removal. This will take O(n * m) time complexity where n is the number of elements after the slice and m is the length of the slice. For a LinkedList, this approach will also traverse the nodes until it reaches the index to be removed and then unlink it. This will take O(n * m) time complexity where n is the average position of the index to be removed and m is the length of the slice.

Note that all above methods modifies the original list. To preserve the original list or work with multiple threads, we may need to create a copy of the list before removing the slice. That’s all about removing the slice from a List in Java.