Difference : ArrayList Vs HashMap

ArrayList and HashMap differ based on following parameters:

1.      Approach

ArrayList stores only the value of the element.

HashMap applies different mechanism as it stores value of the element along with a unique keyassociated to the stored value.

2.      Memory requirement

As ArrayList only stores the value of the element so it requires less memory space in comparision to HashMap.

On other hand HashMap needs to store a unique key for each value so memory requirement increases.

3.      Implementation

ArrayList implements List interface.

HashMap implements Map interface.

4.      Order maintainence

ArrayList ensures that the insertion order is maintained.

HashMap doesn’t guarantee of maintaining insertion order (if you care about order, use LinkedHashMap).

*In case where insertion order is maintained we get the elements returned in same order in which they were inserted while retrieving them.

5.      Null value

Any number of null values can be stored in ArrayList.

Only one null key is allowed in HashMap. But you can store any number of null values.

6.      Duplicate value

ArrayList accepts duplicate values while storing.

HashMap doesn’t accept duplicate Key. But duplicate values are allowed.

7.      Retrieve element

In ArrayList elements can be retrieved specifying index of the element.

In HashMap elements can be retrieved by specifying its Key.

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