DATABASE FUNDAMENTALS
BASICS OF BIG DATA
|
Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
|
|
|
Null values
|
|
|
one null key
|
|
|
None of these
|
|
|
All of these
|
Detailed explanation-1: -A HashMap allows the existence of null keys and values, while a Hashtable doesn’t allow neither null keys, nor null values.
Detailed explanation-2: -Duplicates : ArrayList allows duplicate values while HashSet doesn’t allow duplicates values.
Detailed explanation-3: -An Iterator is an object that enables you to traverse through a collection and to remove elements from the collection selectively, if desired. You get an Iterator for a collection by calling its iterator method. The following is the Iterator interface.
Detailed explanation-4: -No Duplicate Key on HashMap You cannot store duplicate keys in HashMap. However, if you try to store duplicate key with another value, it will replace the value.
Detailed explanation-5: -Q. Which of the following statement is not correct about HashMap class ? HashMap class extends AbstractMap and implements Map interface. HashMap class is not synchronized.