Java LinkedHashMap类

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📜 Java LinkedHashMap类

📅 最后修改于: 2020-10-12 10:06:46 🧑 作者: Mango

Java LinkedHashMap类是Map接口的Hashtable和Linked list实现，具有可预测的迭代顺序。它继承了HashMap类并实现了Map接口。

要记住的要点

Java LinkedHashMap包含基于键的值。
Java LinkedHashMap包含唯一元素。
Java LinkedHashMap可以具有一个null键和多个null值。
Java LinkedHashMap不同步。
Java LinkedHashMap维护插入顺序。
Java HashMap类的初始默认容量为16，负载因子为0.75。

LinkedHashMap类声明

我们来看一下java.util.LinkedHashMap类的声明。

public class LinkedHashMap extends HashMap implements Map

LinkedHashMap类参数

让我们看一下java.util.LinkedHashMap类的参数。

K ：这是此映射维护的键的类型。
V ：这是映射值的类型。

Java LinkedHashMap类的构造方法

Constructor	Description
LinkedHashMap()	It is used to construct a default LinkedHashMap.
LinkedHashMap(int capacity)	It is used to initialize a LinkedHashMap with the given capacity.
LinkedHashMap(int capacity, float loadFactor)	It is used to initialize both the capacity and the load factor.
LinkedHashMap(int capacity, float loadFactor, boolean accessOrder)	It is used to initialize both the capacity and the load factor with specified ordering mode.
LinkedHashMap(Map m)	It is used to initialize the LinkedHashMap with the elements from the given Map class m.

Java LinkedHashMap类的方法

Method	Description
V get(Object key)	It returns the value to which the specified key is mapped.
void clear()	It removes all the key-value pairs from a map.
boolean containsValue(Object value)	It returns true if the map maps one or more keys to the specified value.
Set> entrySet()	It returns a Set view of the mappings contained in the map.
void forEach(BiConsumer action)	It performs the given action for each entry in the map until all entries have been processed or the action throws an exception.
V getOrDefault(Object key, V defaultValue)	It returns the value to which the specified key is mapped or defaultValue if this map contains no mapping for the key.
Set keySet()	It returns a Set view of the keys contained in the map
protected boolean removeEldestEntry(Map.Entry eldest)	It returns true on removing its eldest entry.
void replaceAll(BiFunction function)	It replaces each entry’s value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception.
Collection values()	It returns a Collection view of the values contained in this map.

Java LinkedHashMap示例


import java.util.*;
class LinkedHashMap1{
 public static void main(String args[]){
 
  LinkedHashMap hm=new LinkedHashMap();

  hm.put(100,"Amit");
  hm.put(101,"Vijay");
  hm.put(102,"Rahul");

for(Map.Entry m:hm.entrySet()){
   System.out.println(m.getKey()+" "+m.getValue());
  }
 }
}

Output:100 Amit
       101 Vijay
       102 Rahul

Java LinkedHashMap示例：键值对


import java.util.*;
class LinkedHashMap2{
 public static void main(String args[]){
   LinkedHashMap map = new LinkedHashMap();         
  map.put(100,"Amit");  
 map.put(101,"Vijay");  
 map.put(102,"Rahul");  
   //Fetching key
   System.out.println("Keys: "+map.keySet());
   //Fetching value
   System.out.println("Values: "+map.values());
   //Fetching key-value pair
   System.out.println("Key-Value pairs: "+map.entrySet());
 }
}

Keys: [100, 101, 102]
Values: [Amit, Vijay, Rahul]
Key-Value pairs: [100=Amit, 101=Vijay, 102=Rahul]

Java LinkedHashMap示例：remove()

import java.util.*;
public class LinkedHashMap3 {
   public static void main(String args[]) {
   Map map=new LinkedHashMap();    
 map.put(101,"Amit");  
 map.put(102,"Vijay");  
 map.put(103,"Rahul");  
 System.out.println("Before invoking remove() method: "+map);   
map.remove(102);
System.out.println("After invoking remove() method: "+map);  
   }    
}

输出：

Before invoking remove() method: {101=Amit, 102=Vijay, 103=Rahul}
After invoking remove() method: {101=Amit, 103=Rahul}

Java LinkedHashMap示例：书籍

import java.util.*;  
class Book {  
int id;  
String name,author,publisher;  
int quantity;  
public Book(int id, String name, String author, String publisher, int quantity) {  
    this.id = id;  
    this.name = name;  
    this.author = author;  
    this.publisher = publisher;  
    this.quantity = quantity;  
}  
}  
public class MapExample {  
public static void main(String[] args) {  
    //Creating map of Books  
    Map map=new LinkedHashMap();  
    //Creating Books  
    Book b1=new Book(101,"Let us C","Yashwant Kanetkar","BPB",8);  
    Book b2=new Book(102,"Data Communications & Networking","Forouzan","Mc Graw Hill",4);  
    Book b3=new Book(103,"Operating System","Galvin","Wiley",6);  
    //Adding Books to map 
    map.put(2,b2);
    map.put(1,b1);
    map.put(3,b3);
    
    //Traversing map
    for(Map.Entry entry:map.entrySet()){  
    int key=entry.getKey();
    Book b=entry.getValue();
        System.out.println(key+" Details:");
        System.out.println(b.id+" "+b.name+" "+b.author+" "+b.publisher+" "+b.quantity); 
    }  
}  
}

输出：

2 Details:
102 Data Communications & Networking Forouzan Mc Graw Hill 4
1 Details:
101 Let us C Yashwant Kanetkar BPB 8
3 Details:
103 Operating System Galvin Wiley 6