Last Updated on June 11, 2024 by Abhishek Sharma
In Java, the LinkedHashMap class is a powerful data structure that combines the unique key-value mapping of a HashMap with the predictable iteration order of a LinkedList. This makes it an excellent choice for scenarios where the order of insertion matters, such as maintaining a cache with a defined access order. However, LinkedHashMap does not provide a direct way to access values by index, as it is fundamentally a map rather than a list. Despite this, there are several approaches to retrieve a value by its position in the map. This article explores these methods, providing practical examples and discussing the trade-offs of each approach.
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 2nd index, the key-value pair is [ 3, 4 ], so our output will be 4, the value at the 2nd 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 2nd index, the key-value pair is [ 3, 4 ], so our output will be 4, the value at the 2nd 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 2nd index, the key-value pair is [ 3, 4 ], so our output will be 4, the value at the 2nd 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
Accessing a value by index in a LinkedHashMap requires additional steps since the class itself is not designed for index-based retrieval. By using approaches like iterating through the map’s entry set, converting the map’s values to a list, or leveraging streams, you can achieve this functionality while preserving the benefits of LinkedHashMap. Each method has its pros and cons, and the best choice depends on the specific requirements of your application, such as performance considerations and code readability. Understanding these techniques enhances your ability to utilize LinkedHashMap effectively in various programming scenarios.
FAQs Related to How to Get a Value from LinkedHashMap by Index in Java
Below are some of the FAQs related to How to Get a Value from LinkedHashMap by Index in Java:
Q1: What is a LinkedHashMap in Java?
A LinkedHashMap is a combination of a HashMap and a LinkedList. It maintains the insertion order of its elements, unlike a regular HashMap, which does not guarantee any order.
Q2: Can you directly access an element by index in a LinkedHashMap?
No, LinkedHashMap does not support direct access by index. It is designed to be accessed by keys, not indices.
Q3: How can you get a value from a LinkedHashMap by index?
You can retrieve a value by index by iterating through the map’s entry set, converting the values to a list, or using streams to skip to the desired index.
Q4: What is the most efficient way to access a value by index in a LinkedHashMap?
The most efficient way depends on the size of the map and the frequency of access. Iterating through the entry set is straightforward but may be slower for large maps. Converting to a list provides direct access but involves additional memory usage. Using streams can be concise but might not offer significant performance benefits over iteration.
Q5: Are there any performance considerations when accessing LinkedHashMap values by index?
Yes, accessing values by index is generally less efficient than accessing by key, as it typically requires linear traversal of the map. The performance impact varies based on the size of the map and the method used.
Q6: Can the order of elements in a LinkedHashMap change?
The order of elements in a LinkedHashMap is determined by their insertion order, unless you use a specific access order configuration. Insertion order remains consistent unless elements are removed and reinserted.
Q7: Is LinkedHashMap suitable for large datasets when index-based access is frequently needed?
For large datasets where index-based access is frequently required, LinkedHashMap might not be the best choice due to its lack of direct index-based access. Consider using a different data structure, such as an ArrayList, depending on the use case.