Day_ seventeen

1. LinkedList

Basic use

Introduce

LinkedList : The bottom layer is a two-way linked list , Because it's not continuous storage

It's just that you can find the address of the next element , Therefore, adding and deleting operations are efficient

But the query efficiency is low , Because you can only find one by one from the first

Use

1.1 Underlying implementation

LinkedList : The bottom layer is a two-way linked list , A linked list consists of nodes , Because it's a two-way list , So there are three attributes in the node

1 Saved data Object

2 Next node object   Node type

3 Previous node object   Node type

 

 1.1.2 obtain

get Method

Simulate how subscripts are obtained , It is essentially a traversal operation

 

 2. set

Set characteristic Disordered and unrepeatable , Unordered means that the order of addition and extraction are not guaranteed to be the same

classification : 

HashSet :   At the bottom is a hash table

 TreeSet : At the bottom are red and black trees , The added elements must be sorted according to a certain format

( Numbers : Default from small to large ,    character string : Per person ASCII Code to sort ,    date : Natural date , Yesterday today tomorrow )

Be careful : 

Use TreeSet When , The element must implement Comparable Interface , Because when adding , This interface will be called automatically compareTo Methods for comparison

Add string , Numbers , When it comes to dates , Automatically sort , Because Integer,String,Date Both implement the interface and the method

If we want to store custom types , You need to let this class implement the corresponding interfaces and methods to store

2.1 TreeSet

 

3. Sort

Use TreeSet When , The element must implement Comparable Interface , Because when adding , This interface will be called automatically compareTo Methods for comparison

Add string , Numbers , When it comes to dates , Automatically sort , Because Integer,String,Date Both implement the interface and the method

If we want to store custom types , You need to let this class implement the corresponding interfaces and methods to store

3.1 compareble and comparator

Comparator It is also a comparator class Comparable It's also for comparison , If these two exist at the same time , be Comparator High priority

usage : 

Comparable : If treeSet When saving our own defined types in , Use Comparable

Comparator : If treeSet When the type we write is not saved in , Then use Comparator To specify the collation

such as Integer The default is ascending sort , If we need to sort in descending order , We can only use Comparator, Because we can't change Integer Source code

But this time Integer There is Comparable The implementation of the interface , Equal to two comparisons exist , however Comparator High priority

So it will be sorted according to the rules we define

3.2 List Sort