Is LinkedHashMap ordered?

Yes. See: LinkedHashMap: This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order).

How do I reverse the order of a HashMap?

Method 1: ( Using reverse() method) This method is used to reverse the elements or mappings order in the LinkedHashMap. Parameters: myList is the List provided to the Collections. reverse(myList) method. Returns: It does not return anything but modifies the list internally.

How does LinkedHashMap maintain insertion order?

LinkedHashMap in Java LinkedHashMap maintains the order of insertion. So while iterating over its keys, the elements are returned in the order they were inserted. LinkedHashMap uses a doubly-linked list to maintain the order of insertion. If a key is reinserted, its insertion order is not affected.

What is ordering mode in LinkedHashMap?

A special constructor is provided to create a linked hash map whose order of iteration is the order in which its entries were last accessed, from least-recently accessed to most-recently (access-order). This kind of map is well-suited to building LRU caches.

Is LinkedHashMap values ordered?

So, yes, keySet() , values() , and entrySet() (the three collection views mentioned) return values in the order the internal linked list uses. And yes, the JavaDoc for Map and LinkedHashMap guarantee it.

Why do we use LinkedHashMap?

LinkedHashMap can be used to maintain insertion order, on which keys are inserted into Map or it can also be used to maintain an access order, on which keys are accessed. This provides LinkedHashMap an edge over HashMap without compromising too much performance.

Is LinkedHashMap synchronized?

Most LinkedHashMap operations require synchronization in a multi-threaded environment, even the ones that look pure like get(key) , get(key) actually mutates some internal nodes. The easiest you could do is using Collections. synchronizedMap . Map map = Collections.

What are IdentityHashMap and WeakHashMap?

IdentityHashMap stores strong key reference. WeakHashMap stores the weak key reference. EnumMap stores the strong key reference. Search and get the values. It uses equality operator (==) to search and get the values.

What is the difference between Map and LinkedHashMap?

The key difference between HashMap and LinkedHashMap is order. Elements of a HashMap are not in order, totally random, whereas elements of LinkedHashMap are ordered. The entries of a LinkedHashMap are in key insertion order, which is the order in which the keys are inserted in the Map.

What is load factor in LinkedHashMap?

The load factor is the measure that decides when to increase the capacity of the Map. The default load factor is 75% of the capacity. The threshold of a HashMap is approximately the product of current capacity and load factor.

What is the purpose of LinkedHashMap?

What is a WeakHashMap?

Simply put, the WeakHashMap is a hashtable-based implementation of the Map interface, with keys that are of a WeakReference type. An entry in a WeakHashMap will automatically be removed when its key is no longer in ordinary use, meaning that there is no single Reference that point to that key.

What is IdentityHashMap?

The IdentityHashMap implements Map interface using Hashtable, using reference-equality in place of object-equality when comparing keys (and values). This class is not a general-purpose Map implementation.