Java Interview @ GalaxE India

Hi All,

I hope you all have read my previous Java Interview posts:

• Java Interview @ OrangeMantra
• Java Interview @ SAP
• Java Interview @ Concirrus
• Java Interview @ NexGen Solutions
• Java Interview @ Capgemini
• Java Interview @ Dew Solutions
• Java Interview @ Birdeye
• Java Interview @ RBS
• Java Interview @ Rocketalk

Here, I'm sharing java Interview questions-answers asked in GalaxE.


Question 1:

What are Binary Literal?  How to use them in java?

Answer:

Binary Literals were introduced in java 7. Now using them, we don't need to convert binary to decimal or hexadecimal.

Binary Literals must be started with 0b or 0B.

Binary Literals are used in Protocols, Processors and bitmapped hardware devices.

Example showing their usage:

public class BLiterals{

     public int a = 0b0110;
     public byte b  = (byte) 0b0110;
     public long l = (long) 0b0110L;


    System.out.println("a = "+a);
    System.out.println("b = "+b);
    System.out.println("l = "+l);

}

Output:

a = 6
b = 6
l = 6

Question 2:

Which Application server have you used? Where does it occur in multi-tier architecture?
What benefits we get while using an Application server?

Answer:

I have used Weblogic server.

Weblogic server provide support for Network protocols [HTTPS, SOAP etc.]  It also provides data access and persistence from database server. It also supports SQL transactions for data integrity.

Weblogic also provides security.

So means, when we use Weblogic server , we don't have to care about protocol, security, database integrity, transactions etc. All these are handled by Weblogic itself.
We just have to  focus on business logic.



Question 3:

Write algorithm for Level-Order traversal of a Binary tree.

Answer:

Level-Order traversal means moving from root to leaf step-by step horizontally.

Algorithm for Level-Order Traversal:

1. Check if root node is empty. If yes, then return.
2. If root not null, create a queue and put root node in the queue.
3. Take a while loop on if Queue is not empty.
4. store the size of queue in a variable named size. 
5. Create another while loop inside outer loop. IN this loop, check the value of size variable. It should be > 0. Use size-- in while loop.
6. Now print element[node] from queue. And put all child nodes of that node on queue if these are not null. 
7. Continue from step 5 until it is false and then continue from step 3.

Question 4:

Explain Java Memory Model.

Answer:

Question 5:

Explain JVM memory structure.

Answer:

As per the spec, JVM is divided into 5 virtual memory segments:

• Heap

• Method [Non-heap]

• JVM Stack

• PC Registers

• Native Stack

JVM Stack:

• Has a lot to do with methods in java classes
• Stores local variables and regulates method invocation, partial result and return values.
• Each thread in java has it's own copy of stack and is not accessible to other threads.
• Tuned using -Xss JVM option. 

Native Stack:

• Used for native methods [Non-java code]

Question 6:

What are the common Java Heap related issues?
Answer:

Below is the list of all java heap related issues which occur in java applications at runtime.

• 'OutOfMemory' error due to insufficient Heap
• To identify it, we can use JvisualVM
• To fix it, we can increase heap size or we can revisit the code to see why the demand is high in first place.

• Poor application response time due to long garbage collection pauses
• TO identify it, we can use JvisualVM
• To fix this, we can tune GC [Garbage Collector].

• OutOfMemory error due to memory leak
• To identify it, we can use JvisualVM
• To fix it, we need to analyse the code and correct it.

• Heap Fragmentation
• It is due to when , small and large objects are allocated in a mixed fashion. To some extent, we cannot avoid heap fragmentation -- over time, heap will get fragmented.
• To identify, we see poor application response times, longer GC pauses and in some cases 'OutOfMemory' errors.
• To fix it, tuning can help.

Question 7:

What are the ways to capture Java Heap dump?


Answer:

There are great tools like Eclipse MAT and Heap Hero to analyze Heap dumps. However we need to provide these tools with heap dumps captured in the correct format.

Options to capture  heap dump are:

• Jmap

• Jcmd

• JvisualVM

• JMX

Question 8:

Why reflection is slow? 

Answer:

Reflection needs to inspect metadata in bytecode  instead of just using precompiled addresses and constants.

Everything requires to be searched. That's why reflection is slow.



That's all for this interview post.
Hope this post helps everybody in their java interviews.
Thanks for reading!!