When elements get from the HashMap due to hashing the order they inserted is not maintained while retrieval. We can achieve the given task using LinkedHashMap. The LinkedHashMap class implements a doubly-linked list so that it can traverse through all the elements.
Example:
Input : HashMapInput = {c=6, a=1, b=2}
Output: HashMapPrint = {c=6, a=1, b=2}
Input : HashMapInput = {"first"=1, "second"=3}
Output: HashMapPrint = {"first"=1, "second"=3}
Syntax:
public LinkedHashMap(Map m)
It creates an object of the LinkedHashMap class with the same mappings specified in the original Map object.
Order Not Maintain Here: HashMap Implementation:
Java
// Java Program to maintain insertion order// of the elements in HashMap // Using HashMap (Order not maintain)import java.io.*;import java.util.*;class GFG { public static void main(String args[]) { // creating a hashmap HashMap<String, String> hm = new HashMap<>(); // putting elements hm.put("01", "aaaaaaa"); hm.put("03", "bbbbbbb"); hm.put("04", "zzzzzzz"); hm.put("02", "kkkkkkk"); System.out.println("Iterate over original HashMap"); // printing hashmap for (Map.Entry<String, String> entry : hm.entrySet()) { System.out.println(entry.getKey() + " => " + ": " + entry.getValue()); } }} |
Output
Iterate over original HashMap 01 => : aaaaaaa 02 => : kkkkkkk 03 => : bbbbbbb 04 => : zzzzzzz
Here, the original insertion order of HashMap is [01, 03, 04, 02], but the output is different [01, 02, 03, 04]. It did not maintain the original insertion order of the elements.
Order Maintain Here: LinkedHashMap implementation
Java
// Java Program to maintain insertion order// of the elements in HashMap // LinkedHashMapimport java.io.*;import java.util.*;class GFG { public static void main(String args[]) { // creating a hashmap HashMap<String, String> hm = new LinkedHashMap<>(); // putting elements hm.put("01", "aaaaaaa"); hm.put("03", "bbbbbbb"); hm.put("04", "zzzzzzz"); hm.put("02", "kkkkkkk"); // printing LinkedHashMap System.out.println("Iterate over LinkedHashMap"); for (Map.Entry<String, String> entry : hm.entrySet()) { System.out.println(entry.getKey() + " => " + ": " + entry.getValue()); } }} |
Output
Iterate over LinkedHashMap 01 => : aaaaaaa 03 => : bbbbbbb 04 => : zzzzzzz 02 => : kkkkkkk
