ArrayList
implements List and RandomAccess
- Underlying Data Structure: Resizable Array
- Duplicates - Allowed
- Insertion Order - Preserved
- null insetion - Allowed
- Best choice for: Frequent Retrieval (Random Access)
- Worst choice for: Frequent Insertion/deletion in middle -> Several shift operations are required
- Constructors:
ArrayList l = new ArrayList();ArrayList l = new ArrayList(int initialCapacity);ArrayList l = new ArrayList(Collection C);
- Default initial capacity: 10
- Load factor/fill ratio:
- New Capacity: 1.5C + 1
References are stored contiguously (not the objects).
Comparison with Arrays
| data.structure.primary.array (Private) | ArrayList | |
|---|---|---|
| Definition | An array is a dynamically-created object. It serves as a container that holds the constant number of values of the same type. It has a contiguous memory location. | The ArrayList is a class of Java Collections framework. |
| Size | Static - fixed-length data structure | Dynamic - variable length data structure - can resize itself when needed |
| Size specification | Mandatory to provide size while initializing | Size can be left unspecified - default initial capacity will be used |
| Performance | Fixed size => Faster | Internally backed by array. Resize operation slows down the performance |
| Primitive/generic type | Can store both primitives and objects | Can't store primitives - automatically converts them to objects. For example, int is converted to Integer. |
| Getting the length | arr.length | arr.size() |
| Adding elements | Can add elements using assignment operator | add() function |
| Multiple dimensions | Can be multi-dimensional | CAN'T be multi-dimensional |
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