Difference between HashMap, LinkedHashMap and TreeMap

In Java, HashMap, LinkedHashMap, and TreeMap are all implementations of the Map interface. They are used to store key-value pairs, where the key is used to look up the corresponding value.

Here are some differences between these three implementations:

1. HashMap: HashMap is the most basic implementation of the Map interface. It stores key-value pairs in a hash table, which allows for fast insertion, deletion, and lookup. However, the order of the elements in a HashMap is not guaranteed to be the same as the order in which they were added.

2. LinkedHashMap: LinkedHashMap is a subclass of HashMap that maintains the insertion order of the elements. This means that the elements are iterated in the same order in which they were added to the map. LinkedHashMap is slightly slower than HashMap, but it is useful if you need to maintain the insertion order of the elements.

3. TreeMap: TreeMap is a sorted map implementation that maintains the elements in ascending order based on the keys. TreeMap uses a red-black tree to store the elements, which ensures that the elements are always sorted. TreeMap is slower than HashMap and LinkedHashMap, but it is useful if you need to iterate the elements in a sorted order.

Here is a summary of the differences between these three implementations:

Note that all three implementations are not thread-safe, meaning that they are not suitable for use in multi-threaded environments without external synchronization. To use these implementations in a thread-safe manner, you can use the Collections.synchronizedMap method to wrap the map in a thread-safe wrapper.