HashMap Class in Java

What is HashMap in Java?

Java's HashMap class is a Hash Table implementation of Map interface. It stores data in key-value pairs. 

When to use HashMap in Java?

Unlike an ArrayList, HashMap implementations don't use indices to sort values. Therefore to access each entry, one must know the key of the entry/object.

So if you have several key-value pairs or data that can be identified using keys, then Java's HashMap class is for you.

More about HashMap

The keys used to store data must be unique, which means multiple entries with same key is not possible in HashMap. Also, there's no order to those entries.
The HashMap class extends AbstractMap class and implements the Map interface in Java.

Output

Enter ID:
npl
Enter Password for npl
nplpass
Enter ID:
pkr
Enter Password for pkr
pkrpass
Enter ID:
ktm
Enter Password for ktm
ktmpass
Enter ID:
btl
Enter Password for btl
btlpass
Enter ID:
bkt
Enter Password for bkt
bktpass
Enter ID:
llt
Enter Password for llt
lltpass
Enter ID to query the Password:
pkr
The password for ID: pkr is: pkrpass