Java LinkedHashMap类

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<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：这是此地图维护的键的类型。
• V：这是映射值的类型。

Java LinkedHashMap类的构造方法

Java LinkedHashMap类的方法

Java LinkedHashMap示例

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

  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<Integer, String> map = new LinkedHashMap<Integer, String>();         
	  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<Integer, String> map=new LinkedHashMap<Integer, String>();  	  
	 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<Integer, Book> map=new LinkedHashMap<Integer, Book>();  
    //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<Integer, Book> 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