Both the HashMap and LinkedHashMap data structures are used to map keys to values. However, there are some key differences between these two data structures. The hashmap is a more basic data structure, while the LinkedHashMap allows for more flexibility in how the keys and values are mapped. In general, the hashmap is faster than the LinkedHashMap, but the LinkedHashMap offers greater stability in terms of preserving the order of the key.
What is HashMap?
A HashMap is a data structure that allows you to store key-value pairs. The key is used to retrieve the value from the map. The key can be any data type, but the value must be a reference type. A HashMap uses a hashing algorithm to generate a hashcode for each key. This hashcode is used to index into an array, which stores the values.
When you insert a new key-value pair into the map, the hashing algorithm is used to generate a hashcode for the key. The value is then stored at that index in the array. To retrieve a value from the map, you use the key to generate a hashcode. The value is then retrieved from the array at that index. Hashmaps are often used because they provide efficient lookup time.
What is LinkedHashMap?
A LinkedHashMap is a HashMap with two new features: the order in which elements are added to the map is maintained, and each key can be associated with a value (which can be retrieved later by calling get). LinkedHashMaps are useful for applications that need to keep track of the order in which elements are added or accessed.
Note that a LinkedHashMap does not guarantee that elements will be inserted in the order they were added. If the order is important, you should use an ordered data structure such as a TreeMap instead. The advantage of using a LinkedHashMap is that it provides fast access to elements, even if the number of entries is large.
Difference Between HashMap and LinkedHashMap
Both HashMap and LinkedHashMap are Class in Java that implements Map Interface. Both classes store key/value pairs in a hash table.
- In a HashMap, elements are stored in key/value pair format. In order to store these key/value pairs, HashMap uses the buckets concept. Each key is stored as an object and mapped to its value by using a hashing function.
- LinkedHashMap maintains the insertion-order iteration, which means elements will be returned in the order they were inserted into the map. That’s the only difference between these two Map implementations in Java.
- Another difference between HashMap and LinkedHashMap is that LinkedHashMap provides more options for ordering keys: access order and insertion order but HashMap only provides one: insertion order (the default).
The access-order option maintains a doubly-linked list running through all of the entries in the map, whereby an entry is added to this list after each time it is accessed by calling get(). This option might be beneficial if we have a cache where we want to remove the entry least recently accessed from the cache.”
Conclusion
The HashMap class is part of the Java Collections Framework. The LinkedHashMap extends HashMap and adds a linked list that maintains the order in which entries are added to the map. Both classes store key-value pairs (entries) and both have a get() method that returns the value associated with a given key.
These two data structures differ in how they maintain their ordering – hash tables do not have any specific order, while linked hashmaps use an insertion order. When choosing between these two implementations, it is important to consider your access patterns – if you need fast lookup times and don’t care about the ordering, go with HashMap. If you want entries to be stored and iterated in the order in which they were added, choose LinkedHashMap.
