Java: Java Collections

Difference between ArrayList and LinkedList ?

ArrayList	LinkedList
Random Access [Reading]	Sequential Access [Reading]
Add/Remove elements only at the end [Writing]	Add/Remove elements frequently from the middle of the list [Writing]
Insert/Deletion of the elements is slow.	Insert/Deletion is fast

Difference between ArrayList and Vector ?

ArrayList	Vector
ArrayList is NOT synchronized by default.	Vector List is synchronized by default.
ArrayList can use only Iterator to access the elements.	Vector list can use Iterator and Enumeration Interface to access the elements.
The ArrayList increases its array size by 50 percent if it runs out of room.	A Vector defaults to doubling the size of its array if it runs out of room
ArrayList has no default size.	While vector has a default size of 10.

Difference between List and Set?

List	Set
stores elements in an ordered way	stores elements in an unordered way
may contain duplicate elements	does not contain duplicate elements
allows multiple null element.	allows only one null element

Difference between HashSet and TreeSet ?

HashSet	TreeSet
HashSet does not guarantee for either sorted order or sequence order.	TreeSet provides elements in a sorted order (ascending order).
We can add any type of elements to hash set.	We can add only similar types of elements to tree set.
hashSet organizes data in a hash table (using a hash function).	A treeSet organizes data in a tree through use of Comparator (natural ordering)

TreeSet	HashSet	LinkedHashSet
public class TreeSet extends AbstractSet implements SortedSet, Cloneable, Serializable	public class HashSet extends AbstractSet implements Set,Cloneable,Serializable	public classLinkedHashSet extends HashSet implements Set,Cloneable,Serializable
unique values	unique values	Unique values
It stores its elements in a red-black tree through use of Comparator (natural ordering)	It stores its elements in a hash table(using a hash function).	is implemented as a hash table with a linked list running through it
Order : ascending order	undefined	insertion order
Performance : Slow	better than LinkedHashSet	has fast adding to the start of the list, and fast deletion from the interior via iteration
operations (add, remove and contains)	operations (add, remove,contains and size)	operations (add,contains and remove)

HashMap	HashTable	TreeMap	LinkedHashMap
public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable	public class Hashtable<K,V> extends Dictionary<K,V> implements Map<K,V>, Cloneable, Serializable	public class TreeMap<K,V> extends AbstractMap<K,V> implements NavigableMap<K,V>, Cloneable, Serializable	public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V>
Unidentified Order	Descending Order	Ascending Order	Insertion Order
UnSynchronized	Synchronized	UnSynchronized	UnSynchronized
HashMap allows multiple null values and one null as a key as the key should be unique	Hasttable does not allow any null value as either key or value.	The values can be null. But the key should be unique	The values can be null. But the key should be unique

What are the differences between the Comparable and Comparator interfaces ?

Comparable	Comparator
It uses the compareTo() method. int objectOne.compareTo(objectTwo).	t uses the compare() method. int compare(ObjOne, ObjTwo)
It is necessary to modify the class whose instance is going to be sorted.	A separate class can be created in order to sort the instances.
Only one sort sequence can be created.	Many sort sequences can be created.
It is frequently used by the API classes.	It used by third-party classes to sort instances.

Ref: http://ltiwww.epfl.ch/sJava/version2/Introduction/Collections/index.html

The symbols shown in the figure above define interfaces.

Corresponding Implementations