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Hibernate Interview Question and Answers- Part 6

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1. Explain about version field?

Application level data integrity constants are important if you are making changes to offline information which is again backed by the database. Higher level locking or versioning protocol is required to support them. Version field usage comes at this stage but the design and implementation process is left to the developer.

2. Explain about addClass function?

This function translates a Java class name into file name. This translated file name is then loaded as an input stream from the Java class loader. This addclass function is important if you want efficient usage of classes in your code.

3. Explain about add jar() and add directory() methods?

These methods are the most convenient to use in hibernate. These methods allow you to load all your Hibernate documents at a time. These methods simplify code configuration, refactoring, layout, etc. These functions help you to add your hibernate mapping to Hibernate initialization files.

4. Explain about the id field?

The id field corresponds to the surrogate key which is generated by the database. These fields are handled by the id field. Name attribute is used to specify the names of the field and it should correspond to the method name of get id. This also should correspond to long type and the values should be stored in the database in the long column.

5. What is lazy initialization in hibernate?

Lazy setting decides whether to load child objects while loading the Parent Object. You need to specify parent class. Lazy = true in hibernate mapping file. By default the lazy loading of the child objects is true. This makes sure that the child objects are not loaded unless they are explicitly invoked in the application by calling getChild() method on parent. In this case, hibernate issues a fresh database call to load the child when getChild() is actually called on the Parent object. But in some cases, you do need to load the child objects when a parent is loaded. Just make the lazy=false and hibernate will load the child when a parent is loaded from the database. Examples: Address child of User class can be made lazy if it is not required frequently. But you may need to load the Author object for Book parent whenever you deal with the book for the online bookshop.

Hibernate does not support lazy initialization for detached objects. Access to a lazy association outside of the context of an open Hibernate session will result in an exception.

6. What is DAO?

The Java Data Access Object (Java DAO) is an important component in business applications. Business applications almost always need access to data from relational or object databases and the Java platform offers many techniques for accessing this data. The oldest and most mature technique is to use the Java Database Connectivity (JDBC)API, which provides the capability to execute SQL queries against a database and then fetch the results, one column at a time. Although this API provides everything a developer needs to access data and to persist application state, it is a cumbersome API to develop against – which makes a Java DAO code generator particularly useful.

7. Explain the important feature of DAO?

The Data Access Object design pattern provides a technique for separating object persistence and data access logic from any particular persistence mechanism or API. There are clear benefits to this approach from an architectural perspective. The Java DAO approach provides flexibility to change an application’s persistence mechanism over time without the need to re-engineer application logic that interacts with the Data Access Object tier. For example, there may be performance benefits in changing an application’s performance mechanism from using Entity Beans to using direct JDBC calls from a session bean or even move to an alternative persistence framework, such as Hibernate. Without a Java DAO tier in place, this sort of transition would require extensive re-engineering of existing code.

8. What is connection pooling?

Connection pooling is a technique of creating and managing a pool of connections that are ready for use by any thread that needs them.

This technique of pooling connections is based on the fact that most applications only need a thread to have access to a JDBC connection when they are actively processing a transaction, which usually take only milliseconds to complete. When not processing a transaction, the connection would otherwise its idle. Instead, connection pooling allows the idle connection to be used by some other thread to do useful work.

In practice, when a thread needs to do work against a MySQL or other database with JDBC, it requests a connection from the pool. When the thread is finished using the connection, it returns it to the pool, so that it may be used by any other threads that want to use it.

When the connection is loaned out from the pool, it is used exclusively by the thread that requested it. From a programming point of view, it is the same as if your thread called DriverManager.getConnection() every time it needed a JDBC connection, however with connection pooling, your thread may end up using either a new, or already-existing connection.

9. What is the necessity of connection polling?

Benefits of Connection Pooling:

Connection pooling can greatly increase the performance of your Java application while reducing overall resource usage. The main benefits to connection pooling are:

Reduced connection creation time:

While this is not usually an issue with the quick connection setup that MySQL offers compared to other databases, creating connections still has networking and JDBC driver overhead that will be avoided if connections are recycled.

Simplified programming model:

When using connection pooling, each individual thread can act as though it has created its own JDBC connection, allowing you to use straight-forward JDBC programming techniques.

Controlled resource usage:

If you don’t use connection pooling, and instead create a new connection every time a thread needs one, your application’s resource usage can be quite wasteful and lead to unpredictable behavior under load.

Remember that each connection to MySQL has overhead (memory, CPU, context switches, etc) on both the client and server side. Every connection limits how many resources there are available to your application as well as the MySQL server. Many of these resources will be used whether or not the connection is actually doing any useful work!

Connection pools can be tuned to maximize performance while keeping resource utilization below the point where your application will start to fail rather than just run slower.

10. What is QBECK (que) QC(qbc)?

Quality Center is a comprehensive test management tool. It is a web-based tool and supports the high level of communication and association among various stakeholders (Business Analyst, Developers, Testers etc.), driving a more effective and efficient global application-testing process. Automation Tools like QTP, WinRunner & LoadRunner can be integrated with Quality Center. One can also create reports and graphs for Analysis and Tracking for Test processes.

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Filed in: Z-A Interview Questions

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