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List vs Queue vs Set vs Map

June 27, 2021 Ravi Yasas

	List	Queue	Set	Map
Duplicates	Yes	Yes	No	No(Allow duplicate values not keys)
Order	Yes	Yes	No	No
Null values	Yes	Priority queue doesn't allow, but queue using LinkedList allows null	Single null	Single null key and many null values

HashMap vs HashTable

June 27, 2021 Ravi Yasas

HashMap	HashTable
Not synchronized	Synchronized
Allows one null key and many null values	Doesn't allow null values
No order LinkedHashMap - Insertion order TreeMap - order by keys	No order
No duplicates	No duplicates

June 27, 2021 Ravi Yasas

	ArrayList	LinkedList	Vector
Data structure	Index-based dynamic array	Doubly linked list	Growable array
Increment size	50%	No initial size	100%
Traverse	Uses iterator	Uses iterator	Uses enumeration
Memory usage	Less memory usage	More memory usage
Accessibility	Random and fast	Sequential and slow	Random and fast
Order	Insertion order	Insertion order	Insertion order
Duplicates	Allow	Allow	Allow
Insert / Delete	Slow	Fast	Slow
Synchronized	No	No	Yes
Implements	RandomAccess interface	NA	RandomAccess interface & Serializable interface
Null values	Yes	Yes	Yes

June 27, 2021 Ravi Yasas

Array	ArrayList
Fixed-size	Size is not fixed
Not type-safe	Type-safe
Allow both primitives and objects	Doesn't allow primitives. But after Java 5 auto-boxing will convert primitives to objects

Type safety means the compiler will validate the types while compiling and throw an error if you do anything wrong.

June 26, 2021 Ravi Yasas

Collections	Streams
The collections are used to store & group data in data structures like List, Set, Map...etc.	Streams are used to perform complex operations like filtering, matching, mapping, etc... on stored data
Data modification can be done. You can add or remove data from a Collection	Data cannot be modified
External iterations need to be done	Internal iterations are being used
Collections can be traversed	Streams can be traversed only once. If you need another traverse, you need to create a new stream
Collections are eagerly constructed	Streams are lazily constructed