How to Get a Value from LinkedHashMap by Index in Java

Basically, If we will use linkedhashmap class we can retrieve or fetch the value which is mapped through a parameter which contains a key. So lets just look into a program on how to get value from linkedhashmap in java

LinkedHashMap is a Java predefined class that is similar to HashMap, which contains keys and their respective values. The order of insertion in LinkedHashMap is preserved.

Our objective here is to get a value from the LinkedHashMap by index. We can use many approaches to solve this problem. Let us have a look at the different approaches.

Approach and Algorithm 1 on how to get value from linkedhashmap in java

In this approach, we will convert all the LinkedHashMap keys to a set with the help of keySet() function and then will convert this newly created set to an array with the help of the toArray() function.

As of now, we have an array; we can get a value by index.

Syntax: Object [ ] toArray ( )

Parameters: This function does not take any parameters.

Return Value: The function returns a new array that contains the elements of the set.

Input

[ [1,2] , [3,4] , [5,6] ], Index of the element to be fetched – 2

Output

Value at index 2 is 4

Explanation: As we can see, at the 2^nd index, the key-value pair is [ 3, 4 ], so our output will be 4, the value at the 2^nd index.

Code Implementation on how to get value from linkedhashmap in java

import java.util.*;
import java.io.*;
  
public class PrepBytes {
  
    public static void main(String[] args)
    {

        LinkedHashMap<integer, integer=""> LinkedHMap
            = new LinkedHashMap<integer, integer="">();

        LinkedHMap.put(1, 2);
        LinkedHMap.put(3, 4);
        LinkedHMap.put(5, 6);

        Set<integer> keySet = LinkedHMap.keySet();
  
        Integer[] keyArray
            = keySet.toArray(new Integer[keySet.size()]);
  
        Integer index = 2;
        Integer key = keyArray[index - 1];

        System.out.println("Value at index " + index
                           + " is: " + LinkedHMap.get(key));
    }
}

Output

Value at index 2 is: 4

Time Complexity: The time complexity is O(N), as we are walking over the keyset to convert it to the array.

Space Complexity: The space complexity is O(N), as we are creating an array of N size.

Approach and Algorithm 2 on how to get value from linkedhashmap in java

In this approach, we will first convert the keys of the LinkedHashMap to a set using the LinkedHashMap.keySet() method and then will convert this newly created set to ArrayList using new ArrayList(keySet).

This method converts all the keys to a list-like structure – ArrayList or LinkedList.

Input

[ [1,2] , [3,4] , [5,6] ], Index of the element to be fetched – 2

Output

Value at index 2 is 4

Explanation: As we can see, at the 2^nd index, the key-value pair is [ 3, 4 ], so our output will be 4, the value at the 2^nd index.

Code Implementation on how to get value from linkedhashmap in java

import java.util.*;
import java.io.*;
  
public class PrepBytes {
  
    public static void main(String[] args)
    {

        LinkedHashMap<Integer, Integer> LinkedHMap
            = new LinkedHashMap<Integer, Integer>();

        LinkedHMap.put(1, 2);
        LinkedHMap.put(3, 4);
        LinkedHMap.put(5, 6);

        Set<Integer> keySet = LinkedHMap.keySet();

        List<Integer> listKeys
            = new ArrayList<Integer>(keySet);
  
        Integer index = 2; 
        Integer key = listKeys.get(index - 1);

        System.out.println("Value at index " + index
                           + " is: " + LinkedHMap.get(key));
    }
}

Output

Value at index 2 is: 4

Time Complexity: The time complexity is O(N), as we are walking over the KeySet to convert it to a list.

Space Complexity: The space complexity is O(N), as we are creating a list-like structure that consists of N keys.

Approach and Algorithm 3 on how to get value from linkedhashmap in java

In this approach, we will use Iterators. With the help of entrySet(), we can get all the entries of the LinkedHashMap. After this, we will iterate till the specified index and print the value at that index.

Input

[ [1,2] , [3,4] , [5,6] ], Index of the element to be fetched – 2

Output

Value at index 2 is 4

Explanation: As we can see, at the 2^nd index, the key-value pair is [ 3, 4 ], so our output will be 4, the value at the 2^nd index.

Code Implementation on how to get value from linkedhashmap in java

import java.util.*;
import java.io.*;
  
public class PrepBytes {
    public static void main(String[] args)
    {

        LinkedHashMap<Integer, Integer> LinkedHMap
            = new LinkedHashMap<Integer, Integer>();

        LinkedHMap.put(1, 2);
        LinkedHMap.put(3, 4);
        LinkedHMap.put(5, 6);


        Set<Map.Entry<Integer, Integer> > entrySet
            = LinkedHMap.entrySet();

        Iterator<Map.Entry<Integer, Integer> > iterator
            = entrySet.iterator();
  
        int i = 0;
        int index = 2;
        int value = 0;
  
        while (iterator.hasNext()) {
  
            if (index - 1 == i) {
                value = iterator.next()
                            .getValue(); 
                break;
            }
  
            iterator.next();
            i++;
        }

        System.out.println("Value at index " + index + " is: "
                           + value);
    }
}

Output

Value at index 2 is: 4

Time Complexity: The time complexity is O(N), as we are traversing till the specified index.

Conclusion

So, in the above article we tried to understand how to get the value from linkedhashmap in java. We have also learnt how to use a parameter and key in it to do mapping. The hashmap returns the value null when there is no such key mapping. If you want to solve more questions on Linked List, which are curated by our expert mentors at PrepBytes, you can follow this link Linked List.

FAQs

1. In the linked hash map does the order is preserved?


The Linkedhash map is a predefined class in java which preserves the order of insertion.


2. How to update the value in linked hashmap?


To update the value in linkedhashmap we can use replace method to replace the value through a parameter and the key in it by mapping.


3. Is linked hashmap thread-safe?


In Linkedhashmap we should synchronize the concurrent access to a multithreaded environment explicitly. So, linkedhashmap is not thread safe.