The difference between java map and list

The difference between java map and list

Map (mapping)

Map is a collection that maps key objects and value objects. Each element of it contains a key object and a value object. Map mainly has the following two implementation classes:

HashMap: HashMap is implemented based on a hash table. The cost of inserting and querying is fixed and can be adjusted by setting the capacity and load factor through the constructor. Container performance.

LinkedHashMap: Similar to HashMap, but when iterating through it, the order in which is obtained is its insertion order, or the least recently used (LRU) order.

TreeMap: TreeMap is implemented based on red-black trees. When viewing , they will be sorted. TreeMap is the only Map with a subMap() method, which can return a subtree.

List (list)

The elements of List are stored in a linear manner and can store repeated objects. List mainly has the following two implementation classes:

ArrayList: An array with variable length, which allows random access to elements. Inserting and deleting elements into ArrayList is slow. The implementation of ArrayList expansion in JDK8 is to use the statement newCapacity = oldCapacity (oldCapacity >> 1) (i.e. 1.5 times expansion) in the grow() method to calculate the capacity, and then call the Arrays.copyof() method to copy the original array.

LinkedList: Using linked list data structure, insertion and deletion are fast, but access speed is slow.

Compare	List	Map
Inherited interface	Collection
Common implementation classes	AbstractList (its common subclasses include ArrayList, LinkedList, and Vector)	HashMap, HashTable
Common methods	add( ), remove( ), clear( ), get( ), contains( ), size ( )	put( ), get( ), remove( ), clear( ), containsKey( ), containsValue( ), keySet( ), values( ), size( )
Element	Repeatable	Non-repeatable
Sequence	Ordered
Thread safety	Vector thread safety	Hashtable thread safety

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