LinkedHashMap in Java

LinkedHashMap in Java is Hash table and Linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. It maintains a linked list of the entries in the map, in the order in which they were inserted. This allows insertion-order iteration over the map. That is, when iterating through a collection-view of a LinkedHashMap, the elements will be returned in the order in which they were inserted. You can also create a LinkedHashMap that returns its elements in the order in which they were last accessed.

LinkedHashMap in Java is a generic class which has below declaration:

class LinkedHashMap<K, V>

Here, K specifies the type of keys, and V specifies the type of values.

LinkedHashMap defines the following constructors:

LinkedHashMap( )
LinkedHashMap(Map<? extends K, ? extends V> map)
LinkedHashMap(int capacity)
LinkedHashMap(int capacity, float fillRatio)
LinkedHashMap(int capacity, float fillRatio, boolean Order)

The first form constructs a default LinkedHashMap. The second form initializes the LinkedHashMap with the elements from map. The third form initializes the capacity. The fourth form initializes both capacity and fill ratio. The meaning of capacity and fill ratio are the same as for HashMap. The default capactiy is 16. The default ratio is 0.75. The last form allows you to specify whether the elements will be stored in the linked list by insertion order, or by order of last access. If Order is true, then access order is used. If Order is false, then insertion order is used.



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