My notes about Java collection types comparison.
ArrayList vs. LinkedList
| # | ArrayList | LinkedList |
|---|
| Behavior | Implement List interface, so it can act as a list. | Implement List and Dequeue interface, so it can act as a list and queue both. |
| Storing | Data are stored in a dynamic array. | Data are stored in a doubly-linked list. |
| Manipulation | Slow because it internally uses an array. If any element is removed from the array, all the bits re shifted in the memory. | Faster because it uses a doubly-linked list, so no bit shifting is required in the memory, only the reference link is changed. |
| When to use? | ArrayList is better for storing and accessing data. | LinkedList is better for manipulating data. |
ArrayList vs. Vector
| # | ArrayList | Vector |
|---|
| Synchronization | Non-synchronized, which means that multiple threads can operate on ArrayList at the same time. | Synchronized, which means that only one thread can access the code at a time. |
| Legacy | ArrayList is not legacy class, it was introduced in JDK 1.2. | Vector is legacy class. |
| Size | ArrayList increments 50% of its current size if element added exceeds its capacity. | Vector increments 100% of its current size if element added exceeds its capacity. |
| Speed | ArrayList is fast because it is non-synchronized. | Vector is slow because it is synchronized, i.e., in a multithreading environment, it holds the other threads in runnable or non-runnable state until current thread releases the lock of the object. |
| Iteration | ArrayList uses Iterator interface to traverse through elements. | Vector can use both Iterator or Enumerator interface to traverse through elements. |
| When to use? | ArrayList is use mostly in single-thread applications. | Collections.synchronizedList() is preferred to Vector nowadays. |
List vs. Set
| # | List | Set |
|---|
| Order | Order sequence | Unorder sequence |
| Duplication | Allowed | Disallowed |
| Null element | It is possible to store several null elements. | A null element can only be stored once. |
| Accessing | Elements can be accessed based on their position. | Access to items from a certain position is not permitted. |
| When to use? | Use it when you want to frequently access the elements by using the index. | Set is used when you want to design a collection of distinct elements. |
Set vs. Map
| # | Set | Map |
|---|
| Duplication | Duplicate values are not permitted | Unique key, but repeatable values |
| Traversing | Use Using the keyset() and entryset() methods | Not possible, you must convert Map to Set |
| Insertion Order | Both Set and Map don’t keep the insertion order, however, some of Set’s classes, such as LinkedHashSet, keep the insertion order. | |
HashMap vs. TreeMap
| # | HashMap | TreeMap |
|---|
| Implementation | The Java HashMap implementation of the Map interface is based on hash tables. | Java TreeMap is a Map interface implementation based on a Red-Black Tree structure, which is a self balancing binary search tree. |
| Interface | The Map, Cloneable, and Serializable interfaces are implemented by HashMap. | NavigableMap, Cloneable, and Serializable interfaces are implemented by TreeMap. |
| Null Keys/ Values | null key: allow only one null key, null value: allow multiple. | null key: not permitted, null value: allow multiple. |
| Data Types | HashMap does not perform sorting on keys, so it allows for heterogeneous elements. | TreeMap allows homogeneous values as a key because of sorting. |
| Performance | HashMap is faster than TreeMap because it provides constant time performance that is O(1) for the basic operation like get() and put() | TreeMap is slow in comparison to HaskMap because it provides the performance of O(log(n) for most operation like add(), remove(), and contains(). |
| Order of elements | HashMap does not maintains any order. | TreeMap elements are sorted in natural ordering (ascending). |
| When to use? | Use HashMap when we does not require key-value pair in sorted order | Use TreeMap when we require key-value pair in ascending order. |
