Prevent program runtime errors: Understand common exceptions of Java List interface

In Java programming, the List interface is a very commonly used interface, which provides an ordered, variable-size data structure. We often use List to store and operate a series of elements. However, just because of its common use, we are also prone to encounter various abnormal situations during use. This article will introduce in detail some common exceptions of the Java List interface and how to avoid these exceptions to ensure the normal operation of the program.

1. IndexOutOfBoundsException (out-of-bounds exception)
   When we try to access an index that does not exist in the List, an IndexOutOfBoundsException exception will be thrown. This usually happens in the following two situations:
   a) When we try to get an index that does not exist in the List using the get(int index) method.
   b) When we try to use the add(int index, E element) method to insert an element at an index position that does not exist in the List.

In order to avoid this exception, we should always pay attention to the index range when using List. We can ensure that the index does not go out of bounds by getting the size of the List using the size() method. In addition, when adding elements using the add(E element) method, you do not need to specify an index, which can avoid out-of-bounds exceptions.

2. NullPointerException (null pointer exception)
   When we try to operate on an uninitialized List object, a NullPointerException exception will be thrown. This usually happens in the following situations:
   a) When we use the add(E element) method to add elements to an uninitialized List.
   b) When we use other List methods (such as get(int index), remove(int index), etc.) to operate on an uninitialized List.

In order to avoid this exception, we need to initialize the List object before using the List. That is, create a new instance through the List constructor.

3. UnsupportedOperationException (unsupported operation exception)
   Some methods of the List interface are optional, and whether they are supported depends on the specific implementation class. When we try to operate on an unsupported operation, an UnsupportedOperationException is thrown. This usually happens in the following situations:
   a) When we try to use modification operations such as add(E element) or remove(int index) on an immutable List.
   b) When we try to use the add(int index, E element) method of List to perform an insertion operation on a List that does not support insertion operations.

In order to avoid this exception, when we use List, we need to first determine whether the specific implementation class supports the corresponding operation. You can determine the specific implementation class by using the instanceof keyword, and then handle it according to the specific situation.

4. ConcurrentModificationException (Concurrent Modification Exception)
   When we use an iterator (Iterator) to traverse the List, if a modification operation is performed during the traversal process (such as using the add(E element) of the List Or remove(int index) and other methods), a ConcurrentModificationException exception will be thrown.

In order to avoid this exception, we should use the Iterator's remove() method to perform the deletion operation when traversing the List, instead of directly using the List's remove(int index) method. In addition, if you need to add an operation, you need to complete the traversal first and then add it.

In summary, it is very important to master the common exceptions of the Java List interface, which can help us write more stable and reliable programs. By avoiding these exceptions, we ensure that errors do not occur while the program is running. I hope this article will help you understand and master the method of handling List interface exceptions, and can use it in the actual programming process.

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