Day-17 connection set

Examination supplement
geter/seter Use of methods
for example Declare a variable private String name;
seter Is to set the attribute value , Therefore, it is necessary to enter , Don't worry if you set it up , No need to participate , Therefore, the return value type is void
public void setName(String name){
this.name=name;
}
geter Is to get the attribute value , Therefore, it is necessary to participate （ Return value ）, No input is required , Just get value , It is not to modify the value
public String getName(){
return name;
}

1.LinkedList
① Concept ：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 , So add and delete High efficiency , But the query efficiency is low , Because you can only find one by one from the first
② Common operations ：

 stay LinkedList list=new LinkedList();
    	//ArrayList list=new ArrayList();
    	// Add to tail 
    	list.add(1);
    	list.add(11);
    	list.add(2);
    	list.add(13);
    	// Add to specified location 
    	//list.add(index,element);
    	// Add to head 
    	//list.push(e);
    	//list.addFirst(e);
    	// Tail add 
    	//list.addLast(e);
    	// Number 
    	System.out.println(list.size());
    	// Determine whether it is null 
    	System.out.println(list.isEmpty());
    	// Delete... According to subscript 
    	list.remove(0);
    	// Delete according to data 
    	list.remove(new Integer(11));
    	// Empty 
    	list.clear();
    	// change 
    	list.set(1, 521);
    	// obtain 
    	list.get(2);
    	// Traverse 
    	for(Object object:list){
    
    		
    	}
    } Insert the code chip here 

1.2 Underlying implementation
1.2.1 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

1.2.2 LinkedList class
In order to add more efficiency from beginning to end , stay LinkedList The first and last nodes are saved in the class
1.2.3 add to -add、 obtain -get、
among Get Method just simulates the subscript acquisition method , It is essentially a traversal operation , Just made a certain judgment , Judge whether the first half is fast or the second half is fast

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

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 ASCLL Code to sort
date ： Natural date , Yesterday today tomorrow
2.1 TreeSet

public static void main(String[] args) {
    
		//  Create objects 
		TreeSet set = new TreeSet();
		//  add to 
		set.add(1);
		set.add(2);
		//  because treeSet The elements must be in order , This means that the element types must be unified 
		//  Without unity, there is no comparability , You can't sort 
		// set.add("xxx");
		set.add(22);
		set.add(12);
		set.add(24);
		//  Do not repeat , Do not add if repeated 
		set.add(12);
		System.out.println(set.size());
		System.out.println(set);
		//  Delete by content ,  Cannot delete from index , Because there's no index 
		set.remove(22);
		//  Traverse 
		for (Object object : set) {
    
			System.out.println(object);
		}
		
		set = new TreeSet();
		//  every ASCII Compare 
		set.add("aadddd");
		set.add("aa");
		set.add("acadas");
		set.add("caa");
		set.add("d");
		// a,aa,aadddd,acadas,caa,d
		System.out.println(set);
		
		set = new TreeSet();
		set.add("1");
		set.add("2");
		set.add("3");
		set.add("4");
		set.add("5");
		set.add("6");
		set.add("7");
		set.add("8");
		set.add("9");
		set.add("10");
		// [1, 10, 2, 3, 4, 5, 6, 7, 8, 9]
		System.out.println(set);
	}

2.2Comparable
 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 

2.3 Comparator
Comparator It is also a comparator class Comparable It's also quite , If these two exist at the same time , be Comparator High priority
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
Opening and closing principle : Turn off for changes , For extension development
2.4List Sort

 Here public static void main(String[] args) {
    
		List list = new ArrayList();
		list.add(1);
		list.add(22);
		list.add(3);
		list.add(11);
		//  This method will call the... Of the object Comparable Medium compareTo Method or Comparator Methods in interfaces 
		//  because Integer There is compareTo Method , And in ascending order , That's why you can use sort Method 
		//  For example, if you want to descending order, you can use sort Method overloading 
		// Collections.sort(list);
		Collections.sort(list, new Comparator() {
    

			@Override
			public int compare(Object o1, Object o2) {
    
				// o1  Is the element to be added 
				// o2  It's the elements of the collection 
				Integer i1 = (Integer) o1;
				Integer i2 = (Integer) o2;
				//  The method   return  0  Repeated description , Don't add 
				//  return   Greater than 0 Value   Indicates that the element to be added is larger than that in the collection , Just put it back 
				//  return   Less than 0 Value   Indicates that the element to be added is smaller than the element in the collection , Just put it forward 
				return i2 - i1;
			}
		});
		System.out.println(list);

		list = new ArrayList();
		list.add(new Student1(18));
		list.add(new Student1(11));
		list.add(new Student1(15));
		list.add(new Student1(4));
		//  because Student1 It didn't come true comparable Interface   So it can't be used sort Method 
		// Collections.sort(list);
		//  But you can use overloaded methods 
		Collections.sort(list,new Comparator () {
    
			@Override
			public int compare(Object o1, Object o2) {
    
				return 0;
			}
		});
	}
}

class Student1 {
    
	int age;

	public Student1(int age) {
    
		super();
		this.age = age;
	}
 Insert a piece of code into 

3 summary
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
Opening and closing principle : Turn off for changes , For extension development