An array in Java is a fixed-size data structure that stores elements of the same type. Arrays are a fundamental feature in Java, and they provide efficient storage and access to a sequence of elements. The primary functions of arrays include:
Fixed Size: Once an array is created, its size cannot be changed. This means that you must know in advance how many elements you need to store.
Indexed Access: Elements in an array can be accessed directly via their index, allowing for fast retrieval and update operations. The index is zero-based, meaning the first element is at index 0.
Homogeneous Elements: All elements in an array must be of the same type, ensuring type safety.
Iteration: Arrays can be iterated over using loops, such as for or while loops, or using enhanced for-each loops.
Memory Efficiency: Arrays are stored in contiguous memory locations, which can lead to more efficient memory usage and faster access times due to locality of reference.
An ArrayList is a part of Java’s java.util package and provides a resizable array implementation. Unlike arrays, ArrayList can dynamically grow and shrink as elements are added or removed. The primary functions of ArrayList include:
Dynamic Sizing: ArrayList can automatically resize itself when elements are added or removed. This makes it more flexible compared to arrays.
Indexed Access: Similar to arrays, ArrayList allows indexed access to its elements, enabling fast retrieval and updates.
Generic Support: ArrayList supports generics, allowing for the creation of lists that can hold elements of a specific type, providing type safety at compile-time.
Multiple Utility Methods: ArrayList provides various methods like add(), remove(), get(), set(), size(), clear(), and contains() that simplify many common operations, making it easier to work with compared to arrays.
Iteration: Like arrays, ArrayList can be iterated over using loops, and it also supports iteration through the Iterator and ListIterator interfaces, providing more flexible iteration options.
Size Flexibility: The most significant difference between arrays and ArrayList is size flexibility. Arrays have a fixed size, meaning that once you define the number of elements it can hold, you cannot change it. On the other hand, ArrayList can dynamically resize, allowing you to add or remove elements without worrying about running out of space.
Type Safety: Arrays are type-specific from the start, while ArrayList is generic, allowing the type to be defined when the ArrayList is instantiated. This generic nature of ArrayList provides additional type safety at compile-time.
Performance: Due to the dynamic resizing capability of ArrayList, it can be slower than arrays, especially when dealing with large datasets or frequent additions and deletions. Arrays, with their fixed size, can be more efficient in terms of memory usage and access time since they don't need to resize or reallocate memory.
Primitive Types: Arrays can hold primitive types (e.g., int, char, boolean), whereas ArrayList can only hold objects. This means if you need to store primitives in an ArrayList, they must be wrapped in their corresponding wrapper class (e.g., Integer, Character, Boolean).
Utility Methods: ArrayList provides a broader range of built-in methods for list manipulation, making it more versatile and easier to work with compared to the basic array.