This is a helpfull website to start https://www.bigocheatsheet.com/

Basic Data Structures

Arrays

https://docs.oracle.com/javase/specs/jls/se8/html/jls-10.html https://www.javatpoint.com/array-in-java#:~:text=Java%20array%20is%20an%20object,in%20a%20contiguous%20memory%20location.&text=Java%20array%20inherits%20the%20Object,in%20an%20array%20in%20Java. Arrays in Java

• fixed size
• sequential in memory
• similar data types
• inherits the Object, implements the Serializable and Cloneable interfaces
• int numbers[]=new int[5]; declaration and instantiation
• int numbers[]={33,3,4,5}; declaration, instantiation and initialization

ArrayList

https://www.javatpoint.com/difference-between-arraylist-and-linkedlist

• It store data on an internal array transient Object[] elementData
• It can not store primitive types

• It has 3 constructors in Java 8, Java 7 has version only has 1 constructor

  1. ArrayList someArray = new ArrayList();
  2. new ArrayList(7) //default capacity is 10
  3. new ArrayList(new LinkedList())
• Manipulation is slow because it internally uses an array. If any element is removed from the array, all array will be shifted
• It grows dynamically, If arraylist is full it create a new arraylist with %50 more capacity and copy all elements the bits are shifted in memory.
• better for storing and accessing

LinkedList

• internally uses a doubly linked list to store the elements
• better for manipulating
• it implements List, Deque, Cloneable, java.io.Serializable

https://javaconceptoftheday.com/hashset-vs-linkedhashset-vs-treeset-in-java/

HashSet

• All items are unique
• implements Set interface backend by hashtable which is actually hashmap
• doesn’t preserve the order
• objects are inserted as based on their hashcode
• NULL is not allowed
• implements Serializable and Cloneable interfaces

LinkedHashSet

TreeSet

ConcurrentHashMap

• it uses volatile semantics for get(key)

  ConcurrentSkipListMap

• isn’t so fast, but is useful when you need sorted thread-safe map

• expected average log(n) time cost for the containsKey, get, put and remove operations and their variants

  TreeMap

  computeIfAbsent

  computeIfPresent