Array
An array is a set of elements of the same data type that are arranged in an array of fixed size. The index or key of each member in the array uniquely identifies it. The majority of computer languages have static arrays, which means that their size is fixed and cannot be altered while the program is running.
- Declaration: An array's size is specified when it is declared, for example, int[] numbers = new int[5];.
- Size: The size of the elements is fixed and must be known ahead of time.
- Type: Homogeneous; each component needs to have the same kind of data.
- Memory Allocation: Constant memory allocation has the potential to waste memory.
- Flexibility: Limited ability to change size while the program is running.
ArrayList
In Java (and other languages where such structures exist), an ArrayList is a dynamic data structure that resembles an array and has the ability to dynamically expand or contract in size. The Java Collections Framework includes it.
- Declaration: ArrayLists, like ArrayList<Integer> numbers = new ArrayList<>();, are defined without mentioning their size.
- Size: dynamic; subject to change while the program runs.
- Type: Heterogeneous; capable of storing several data kinds' components.
- Memory Allocation: More memory-efficient, non-contiguous memory allocation.
- Flexibility: Greater flexibility due to the ease of adding and removing components.
What are the Differences between an Array and an Arraylist?
- Size Flexibility: The size of an array is fixed and set at declaration time. Whereas The size of an arraylist is dynamic and can be changed in real-time.
- Memory Allocation: Contiguous memory allocation in an array has the potential to waste memory. On the other hand, non-contiguous memory allocation is more memory-efficient in Arraylist.
- Syntax: Fixed-size array declared as int[] numbers = new int[5];. On the other hand, arraylists like ArrayList<Integer> numbers = new ArrayList<>(); are declared without a size specified.
- Type of Elements: Arrays are homogeneous in the sense that all elements must be of the same data type, whereas arraylists are heterogeneous in the sense that they can store elements of different data types.
- Performance: Since elements of arrays are kept in contiguous memory locations, arrays generally have faster access times than arraylists, which are slower due to non-contiguous memory allocation and additional functionality.
Conclusion
Arrays are static, homogeneous data structures with contiguous memory allocation, whereas ArrayLists are dynamic, heterogeneous data structures with non-contiguous memory allocation. The choice depends on the program's specific requirements, such as the need for a fixed or dynamic size and the type of elements to be stored. ArrayLists offer greater flexibility and functionality than arrays but at a slight performance cost.