Interview Questions

Benefits of IOC

-       Minimises code – no need to worry about creation

-       Testable

-       Loose coupling – Factory pattern – more intrusive owing to explicitly requesting for compoenents

-       Eager instantiation and lazy loading

Dependency Injections vs JNDI

-       String based name

-       Lookup code is verbose

-       Retrieved objects are not checked at compile-time

Describe Spring framework?

Difference between Bean factory and Application Context?

Core Container provides the essential basic functionality. The basic package in the spring framework is the org.springframework.beans package. The Spring framework uses JavaBeans and there are two ways in which clients can use the functionality of Spring framework -- BeanFactory and ApplicationContext. BeanFactory applies the IOC pattern and separates an application’s configuration and dependency specification from the actual application code.

Spring Application Context is a configuration file that provides context information to Spring framework. The ApplicationContext builds on top of the BeanFactory and inherits all the basic features of Spring framework. In addition to basic features, ApplicationContext provides additional features like event management, internalization support, resource management, JNDI, EJB, email, and scheduling functionality.

BeanFactory is useful in low memory situations, which does not have the excess baggage an ApplicationContext has. ApplicationContext assist the user to use Spring in a framework oriented way while the BeanFactory offers a programmatic approach.

RMI vs JMS

Are messaging applications slow? While there is some overhead in all messaging systems, but this does not

mean that the applications that are using messaging are necessarily slow. Messaging systems can achieve a

throughput of 100 messages per second depending on the installation, messaging modes (synchronous versus

asynchronous, persistent versus non-persistent), and acknowledgment options such as auto mode, duplicates

okay mode, and client mode etc. The asynchronous mode can significantly boost performance by multi-tasking.

For example: In an Internet based shopping cart application, while a customer is adding items to his/her shopping

cart, your application can trigger an inventory checking component, and a customer data retrieval component to

execute concurrently.

Are messaging applications reliable? This is basically a trade-off between performance and reliability. If

reliability is more important then the:

• Acknowledgment option should be set to automode where once only delivery is guaranteed
• Message delivery mode should be set to persistent where the MOM writes the messages to a secure

storage like a database or a file system to insure that the message is not lost in transit due to a system

failure.

Exception Handling?

ACEGI Security Framework –

• Authentication
• authorization ((J2EE declarative & programmatic)
• Data Integrity
• Confidentiality and privacy
• Non-repudiation and auditing

Java concepts:

1)     When would we use Vector/hashtable vs ArrayList/HashMap?

2)     Can you tell me something about Garbage collection in Java.. When does it occur, how does it perform it?

3)     Describe any memory leak you have encountered and how to go about detecting and minimizing them? Weak references

4)     What is a singleton pattern? How do you code it in Java?

A singleton is a class that can be instantiated only one time in a JVM per class loader. Repeated calls always

return the same instance. Ensures that a class has only one instance, and provide a global point of access. It

can be an issue if singleton class gets loaded by multiple class loaders.

public class OnlyOne {

private static OnlyOne one = new OnlyOne();

private OnlyOne(){… } //private constructor. This class cannot be instantiated from outside.

public static OnlyOne getInstance() {

return one;

}

}

To use it:

//No matter how many times you call, you get the same instance of the object.

1)     OnlyOne myOne = OnlyOne.getInstance();

Program:

Write a JAVA function that deletes chars from a String. Any character in remove must be deleted from str. Justify any design decisions & discuss the time and space efficiency of the solution?

Good architecture?

1.1 Design Goals

Trial center must meet these above goals with a well designed architecture.  Specifically, the Trial Center architecture must be designed to meet the following goals and objectives.

• Performance – Trial Center must provide speedy response times and efficient navigation.
• Scalability – Must provide the ability to scale from low to high (thousands) of users.
• Maintainability – Trial Center must be easy to support and maintain.  The design must accommodate changes to the slicing/dicing of operational metrics without requiring changes to the source system publishers (to the degree possible).
• Availability – Since Trial Center will be a single point of entry for all studies, the product and metrics it displays must support 99.9% uptime.
• Near Real Time – Changes to operational metrics should be reflected in Trial Center within 3 – 5 seconds of being committed in a source system.
• Reliability – The operational data presented must be consistent with the data located in original systems.
• Aggregation – Trial Center establishes a platform for aggregating operational metrics across all the systems involved in a study. 

1.2 Performance

Trial Center will serve as a data aggregator across systems.  This data will grow in size as more studies come online.  The system must be designed to support strategies to provide efficient indexing of data for filtering and aggregation purposes. When appropriate, metric totals may need to be persisted and maintained in order to reduce the number of computation requests to the database.  The system must also take advantage of a caching strategy to improve performance and reduce the general number of database requests to the Trial Center repository.

1.3 Scalability

Trial Center’s application server must be able to scale horizontally.  Trial center must be able to be supported in a web farm environment.  In order to support this, trial center must not hold state full information in one app server.  Any data state must either be stored in the central repository or be distributed over an in-memory distributed cache server.  This will allow the system to be load balanced as the number of users requests grow.

1.4 Maintainability

Trial Center will be designed in a very modular manner.  Trial Center will adhere to a separation of concerns approach to modular design and approach a more interface based development philosophy.  Trial center will be tiered, whereby each tier will be responsible for specific functionality.  Dependency Injection will be used to decouple the tiers.  This will ensure a clean separation between the business layers.

Additionally, the web framework will be built using MVC architecture.  This will create a clean separation between HTML design and business logic.

1.5 Availability

Trial Center will support a clustering deployment option.  Clustering is generally defined as two or more web servers that closely cooperate with each other to ensure that each server in the group presents the same data to the end user.  High availability will be achieved through the use of creating redundant servers that can be switched over when a failure occurs on the main server.

1.6 Near Real-Time

Data that is presented using Trial Center will be sourced by other systems.  Other systems will push data to Trial Center when the transaction occurs in the source systems.  This will allow the consolidation of the data to be applied in a timely manner.  In general, data from source system must push the data into Trial Center within 3-5 seconds.

1.7 Reliability

Since data will be sourced from multiple systems, Trial Center must show data that represents the current state.  Counts in Trial Center must match the current counts in the source system.  In order to accomplish this, the data must arrive in a timely manner and the messaging transport must be reliable. No missed transactions can ever occur during transport.