Java Foundation--Set analysis

Java Collection

When does an array seem to be too weak to meet demand and need a collection class?

1. Don't know the exact length of the data
2. Need to sort automatically
3. Store key value pairs

Of course, the above situation is not absolute, but the array is more difficult to meet. The collection class (also known as the Container Class) shows its powerful features.

Classification of collection classes (Pictures from http://biancheng.dnbcw.info/1000wen/359774.html)

Does not contain the queue content, the implementation class for some maps is not given.

Common uses are list, Set, map, and their implementation classes.

List, Set, and map interfaces and the characteristics of each implementation class

Interface	Characteristics	Implementation class	Implementing Class Attributes	Member Requirements
List	Linear, ordered storage container that accesses elements through an index	ArrayList	Array implementations. Non-synchronous.
		Vector	Similar to ArrayList, synchronous.
		LinkedList	Doubly linked list. Non-synchronous.
Map	Save a key-value pair member	HashMap	The implementation of Map interface based on hash table to meet the common requirements	Any of the object objects, if you modify the Equals method, you need to modify the Hashcode method at the same time
		TreeMap	Sort by default according to natural order, or sort according to the comparator provided when the mapping is created	Key members require implementation of the Caparable interface, or use comparator to construct treemap. Key members are generally of the same type.
		Linkedhashmap	Similar to HashMap, but the order in which "key-value pairs" are obtained when iterating through is the order in which they are inserted or least recently used	Same as HashMap
		Identityhashmap	Hash map to compare "key value" with = = instead of equals ()	Members are judged equal by = =
		Weakhashmap	Weak key mapping, which allows you to release the object that the map points to
		Concurrenthashmap	Map of linear security
Set	Members cannot be duplicated	HashSet	Set for quick Find design	element must be defined hashcode ()
		TreeSet	The set of the hold order, the bottom is the tree structure	Element must implement comparable interface
		Linkedhashset	Internal use of the chain list to maintain the order of elements (inserted order)	element must be defined hashcode ()

In case of meeting the requirements, map should use Hashmap,set as far as possible using HashSet.

Basic use of collection classes

List

List basic operations

Comparison of efficiency between ArrayList and LinkedList

ArrayList the efficiency of adding elements

Execution Time Comparison

Number of executions (inserted at position No. No. 0)	ArrayList time (MS)	LinkedList Time (MS)
10000	31	0
20000	141	0
40000	484	16
80000	1985	0
160000	7906	0
320000	31719	16
Number of executions (insert at tail)	ArrayList time (MS)	LinkedList Time (MS)
10000	0	0
20000	15	0
40000	0	0
80000	0	0
160000	0	15
320000	0	16
Number of cyclic outputs (get (index) method)	ArrayList time (MS)	LinkedList Time (MS)
10000	93	204
20000	188	797
40000	328	2734
80000	38]	13328
160000	1594	62313
320000	2765	Too long ...

Because the ArrayList is implemented by an array, all elements of the list are moved when inserted at position No. 0, and no movement is required to insert the element at the end. LinkedList is a doubly linked list, and it takes the same amount of time to insert elements at any location. So you should use LinkedList to improve efficiency when there are more insertions and deletions in the list, while there are more index queries using ArrayList (using enhanced for loops or iterator traversal linkedlist efficiency will be much higher).

Arrays are a very common data structure, and most programs are related to arrays when you start to touch programming. Just beginning to touch Java is also always use the array to write some programs, and then more and more think that the array this thing can not meet the demand, then a "senior" to me said: Do not use the collection class is equal not learned java. Then we know that there is a collection class.

Think about 3, 4 years ago, time is like fleeting ah.

When does an array seem to be too weak to meet demand and need a collection class?

1. Don't know the exact length of the data
2. Need to sort automatically
3. Store key value pairs

Of course, the above situation is not absolute, but the array is more difficult to meet. The collection class (also known as the Container Class) shows its powerful features.

Classification of collection classes (Pictures from http://biancheng.dnbcw.info/1000wen/359774.html)

Does not contain the queue content, the implementation class for some maps is not given.

Common uses are list, Set, map, and their implementation classes.

List, Set, and map interfaces and the characteristics of each implementation class

Interface	Characteristics	Implementation class	Implementing Class Attributes	Member Requirements
List	Linear, ordered storage container that accesses elements through an index	ArrayList	Array implementations. Non-synchronous.
		Vector	Similar to ArrayList, synchronous.
		LinkedList	Doubly linked list. Non-synchronous.
Map	Save a key-value pair member	HashMap	The implementation of Map interface based on hash table to meet the common requirements	Any of the object objects, if you modify the Equals method, you need to modify the Hashcode method at the same time
		TreeMap	Sort by default according to natural order, or sort according to the comparator provided when the mapping is created	Key members require implementation of the Caparable interface, or use comparator to construct treemap. Key members are generally of the same type.
		Linkedhashmap	Similar to HashMap, but the order in which "key-value pairs" are obtained when iterating through is the order in which they are inserted or least recently used	Same as HashMap
		Identityhashmap	Hash map to compare "key value" with = = instead of equals ()	Members are judged equal by = =
		Weakhashmap	Weak key mapping, which allows you to release the object that the map points to
		Concurrenthashmap	Map of linear security
Set	Members cannot be duplicated	HashSet	Set for quick Find design	element must be defined hashcode ()
		TreeSet	The set of the hold order, the bottom is the tree structure	Element must implement comparable interface
		Linkedhashset	Internal use of the chain list to maintain the order of elements (inserted order)	element must be defined hashcode ()

In case of meeting the requirements, map should use Hashmap,set as far as possible using HashSet.

Basic use of collection classes

List

List basic operations

Comparison of efficiency between ArrayList and LinkedList

ArrayList the efficiency of adding elements

Execution Time Comparison

Number of executions (inserted at position No. No. 0)	ArrayList time (MS)	LinkedList Time (MS)
10000	31	0
20000	141	0
40000	484	16
80000	1985	0
160000	7906	0
320000	31719	16
Number of executions (insert at tail)	ArrayList time (MS)	LinkedList Time (MS)
10000	0	0
20000	15	0
40000	0	0
80000	0	0
160000	0	15
320000	0	16
Number of cyclic outputs (get (index) method)	ArrayList time (MS)	LinkedList Time (MS)
10000	93	204
20000	188	797
40000	328	2734
80000	688	13328
160000	1594	62313
320000	2765	Too long ...

Because the ArrayList is implemented by an array, all elements of the list are moved when inserted at position No. 0, and no movement is required to insert the element at the end. LinkedList is a doubly linked list, and it takes the same amount of time to insert elements at any location. So you should use LinkedList to improve efficiency when there are more insertions and deletions in the list, while there are more index queries using ArrayList (using enhanced for loops or iterator traversal linkedlist efficiency will be much higher).

Java Foundation--Set analysis