Java ArrayList Basics: Dynamic Array Operations, A Must-Learn for Beginners

The `ArrayList` in Java is a dynamic array class under the `java.util` package, which implements automatic expansion, has a variable length, and is more flexible than ordinary arrays, making it suitable for storing data with an uncertain length. Its core advantage is that it does not require manual specification of length and provides convenient methods for adding, deleting, modifying, querying, and traversing elements. Basic operations: To create an `ArrayList`, you need to import the package and specify the generic type (e.g., `<String>`). You can also specify an initial capacity (e.g., `new ArrayList<>(10)`). Elements are added using `add()` (either at the end or inserted at a specified position); elements are retrieved using `get(index)` (indexes start from 0, and an exception is thrown if out of bounds); modification is done with `set(index, e)`; deletion can be done using `remove(index)` or `remove(e)` (the latter deletes the first matching element). Traversal is supported via ordinary for loops, enhanced for loops, and iterators. Dynamic expansion: The initial capacity is 10. When the number of elements exceeds the capacity, it automatically expands to 1.5 times the original capacity without manual processing. Precautions: The index must be between 0 and `size()-1`. The generic types must be consistent, and only the first occurrence of a duplicate element is deleted. Mastering its operations can enable efficient handling of data collections with uncertain lengths.