Java教程-Java LinkedHashMap类

Java LinkedHashMap类

Java LinkedHashMap类是Map接口的Hashtable和链表实现，具有可预测的迭代顺序。它继承自HashMap类并实现了Map接口。

需要记住的要点

• Java LinkedHashMap根据键存储值。
• Java LinkedHashMap包含唯一元素。
• Java LinkedHashMap可以有一个null键和多个null值。
• Java LinkedHashMap是非同步的。
• Java LinkedHashMap保持插入顺序。
• Java HashMap类的初始默认容量为16，负载因子为0.75。

LinkedHashMap类声明

让我们看一下java.util.LinkedHashMap类的声明。

1. public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V>

LinkedHashMap类参数

让我们看一下java.util.LinkedHashMap类的参数。

• K：这是该映射维护的键的类型。
• V：这是映射的值的类型。

Java LinkedHashMap示例

1. **import** java.util.*; 
2. **class** LinkedHashMap1{ 
3.  **public** **static** **void** main(String args[]){ 
4.   
5.  LinkedHashMap<Integer,String> hm=**new** LinkedHashMap<Integer,String>(); 
6.  
7.  hm.put(100,"Amit"); 
8.  hm.put(101,"Vijay"); 
9.  hm.put(102,"Rahul"); 
10.  
11. **for**(Map.Entry m:hm.entrySet()){ 
12.   System.out.println(m.getKey()+" "+m.getValue()); 
13.  } 
14.  } 
15. } 
Copy code
输出：
100 Amit
101 Vijay
102 Rahul

Java LinkedHashMap示例：键-值对

1. **import** java.util.*; 
2. **class** LinkedHashMap2{ 
3.  **public** **static** **void** main(String args[]){ 
4.   LinkedHashMap<Integer, String> map = **new** LinkedHashMap<Integer, String>();      
5.    map.put(100,"Amit");  
6.    map.put(101,"Vijay");  
7.    map.put(102,"Rahul");  
8.     //获取键 
9.     System.out.println("Keys: "+map.keySet()); 
10.     //获取值 
11.     System.out.println("Values: "+map.values()); 
12.     //获取键值对 
13.     System.out.println("Key-Value pairs: "+map.entrySet()); 
14.  } 
15. } 
mathematicaCopy code
输出：
Keys: [100, 101, 102]
Values: [Amit, Vijay, Rahul]
Key-Value pairs: [100=Amit, 101=Vijay, 102=Rahul]

Java LinkedHashMap示例：remove()

1. **import** java.util.*; 
2. **public** **class** LinkedHashMap3 { 
3.   **public** **static** **void** main(String args[]) { 
4.   Map<Integer,String> map=**new** LinkedHashMap<Integer,String>();    
5.    map.put(101,"Amit");  
6.    map.put(102,"Vijay");  
7.    map.put(103,"Rahul");  
8.    System.out.println("Before invoking remove() method: "+map);   
9.   map.remove(102); 
10.   System.out.println("After invoking remove() method: "+map);  
11.   }   
12. } 

输出：

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

Java LinkedHashMap示例：Book

1. **import** java.util.*;  
2. **class** Book {  
3. **int** id;  
4. String name,author,publisher;  
5. **int** quantity;  
6. **public** Book(**int** id, String name, String author, String publisher, **int** quantity) {  
7.   **this**.id = id;  
8.   **this**.name = name;  
9.   **this**.author = author;  
10.   **this**.publisher = publisher;  
11.   **this**.quantity = quantity;  
12. }  
13. }  
14. **public** **class** MapExample {  
15. **public** **static** **void** main(String[] args) {  
16.   //Creating map of Books  
17.   Map<Integer,Book> map=**new** LinkedHashMap<Integer,Book>();  
18.   //Creating Books  
19.   Book b1=**new** Book(101,"Let us C","Yashwant Kanetkar","BPB",8);  
20.   Book b2=**new** Book(102,"Data Communications & Networking","Forouzan","Mc Graw Hill",4);  
21.   Book b3=**new** Book(103,"Operating System","Galvin","Wiley",6);  
22.   //Adding Books to map  
23.   map.put(2,b2); 
24.   map.put(1,b1); 
25.   map.put(3,b3); 
26.    
27.   //Traversing map 
28.   **for**(Map.Entry<Integer, Book> entry:map.entrySet()){  
29.     **int** key=entry.getKey(); 
30.     Book b=entry.getValue(); 
31.     System.out.println(key+" Details:"); 
32.     System.out.println(b.id+" "+b.name+" "+b.author+" "+b.publisher+" "+b.quantity);  
33.   }  
34. }  
35. }  

输出：