Java Collection: List, set, MAP, hashmap, hashtable, Vector

List, set, MAP, hashmap, hashtable, VectorCollection interface: In general development, the collection interface is usually not directly used to store data for clear purposes.

· Sub-interface: List

· Sub-interface: Set

Since list is an interface, you must use the subclass-> arraylist

If you want to use list, the format is: List L = new arraylist ();

 

★Difference between list and set:

1. List-element sequence, set-class set without repeated Elements

2. The basic usage of the set is the same as that of the list, but the hashset sub-classes are unordered during storage (Hash Storage)

3. Differences between element duplication and order:

· The data in the list can be retained by repeated elements.

· Duplicate elements are not allowed for data in the Set, and duplicate elements are replaced. // duplicate elements are overwritten, leaving only one

If hashset is used in a set, it is stored unordered by hash. If you want to store it in sequence, use the treeset subclass. Sort by comparable Interface

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★Map:

Save a pair of values (MAP ):

|-Hashmap: asynchronous processing, new class

|-Hashtable: synchronous processing, old class

|-Treemap: A set sorted by key

Elements are a collection of binary even pairs and cannot be repeated.

Each time you store a pair of values:Key-> Value

The main function of map is to use it as search, rather than as output. (Map for search data)

* Data Storage Method:

-Put (Object key, object value)

* Get content (based on the key ):

-Cobject get (Object key)

Objects of the map interface cannot be output directly using iterator.

To use iterator to output the content of the map interface object, follow these steps:
Map-> set-> iterator-> map. Entry-> key, values

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★Hashmap class

-The hashmap class uses a hash to implement the map interface.

-Hashmap is a ing Class (key-> value: Key-Value Pair)

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★Hashtable

-Similar to hashmap, but hashtable is synchronous

-Ing (key-> value: Key-Value Pair)

-Hashtable does not support iterative functions.

Properties class

-The properties class is a subclass of the hashtable class (hashtable <-properties)

-List of values to be kept

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☆Property class-Properties

(Properties-> string; hashtable-> Object)

Unlike hashtable, the properties class stores strings while hashtable stores objects.

-Setproperty (string key, string value)

-Getproperty (string key)

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★Treemap class(Sort by key)

-The treemap class can sort data.

-Quick Search

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★Vector

|-List: Repeated elements are allowed.

|-Arraylist: asynchronous processing. The new class can only be output using iterator.

|-Vector: synchronous processing. The old class can be output simultaneously with iterator and enumeration.

Neither list nor set can use enumeration output.

Another subclass of list: vector can use enumeration to output

Vector

-Implement Dynamic Array Using Vector

-The vector is synchronized.

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