Software Development

Lambda Expressions
Lambda expression helps us to write our code in functional style. It provides a clear and concise way to implement SAM interface(Single Abstract Method) by using an expression. It is very useful in collection library in which it helps to iterate, filter and extract data.

Method References
Java 8 Method reference is used to refer method of functional interface . It is compact and easy form of lambda expression. Each time when you are using lambda expression to just referring a method, you can replace your lambda expression with method reference.

Functional Interface
An Interface that contains only one abstract method is known as functional interface. It can have any number of default and static methods. It can also declare methods of object class. Functional interfaces are also known as Single Abstract Method Interfaces (SAM Interfaces).

Optional
Java introduced a new class Optional in Java 8. It is a public final class which is used to deal with NullPointerException in Java application. We must import java.util package to use this class. It provides methods to check the presence of value for particular variable.

Date/Time API
Java has introduced a new Date and Time API since Java 8. The java.time package contains Java 8 Date and Time classes.

HashMap in Java is basically an array of buckets (also known as bucket table of HashMap) where each bucket uses linked list to hold elements. A linked list is a list of nodes where each node contains a key-value pair.
In simple words, a bucket is a linked list of nodes where each node is an object of class Node. The key of the node is used to obtain the hash value and this hash value is used to find the bucket from Bucket Table.
HashMap works on the principle of hashing data structure or technique that uses an object’s hashcode to place that object inside the map.
Hashing involves Bucket, Hash function (hashCode() method), and Hash value. It provides the best time complexity of O(1) for insertion and retrieval of objects.
Therefore, it is the best-suited data structure for storing key-value pairs that later on can be retrieved in minimum time.

Hash code of key may be large enough to create an array. hash code generated may be in the range of integer and if we create arrays for such a range, then it will easily cause outOfMemoryException. So we generate index to minimize the size of array. Basically following operation is performed to calculate index. 
index = hashCode(key) & (n-1).
where n is number of buckets or the size of array.

The hashCode() method should return the same integer value for the same object for each calling of this method unless the value stored in the object is modified.
If two objects are equal(according to equals() method) then the hashCode() method should return the same integer value for both the objects.
But, it is not necessary that the hashCode() method will return the distinct result for the objects that are not equal (according to equals() method).

Tip 1 : The cross questioning can go intense some time, think before you speak.

Tip 2 : Be open minded and answer whatever you are thinking, in these rounds I feel it is important to have opinion.

Tip 3 : Context of questions can be switched, pay attention to the details. It is okay to ask questions in these round, like what are the projects currently the company is investing, which team you are mentoring. How all is the work environment etc.