Interface Java Interview Questions – Set 11

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Define TaskTracker.

TaskTracker is a node in the cluster that accepts tasks like MapReduce and Shuffle operations from a JobTracker.

What is the difference between HDFS and NAS?

HDFS data blocks are distributed across local drives of all machines in a cluster whereas, NAS data is stored on dedicated hardware.

What is the purpose of button groups?

Button groups are used for the placement of more than one buttons in the same line.

What is an enumeration

An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It is a construct which collection classes return when you request a collection of all the objects stored in the collection. It allows sequential access to all the elements stored in the collection.

What is an Iterator

Some of the collection classes provide traversal of their contents via a java.util.Iterator interface. This interface allows you to walk through a collection of objects, operating on each object in turn. Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator.

Difference between Vector and ArrayList

Vector & ArrayList both classes are implemented using dynamically resizable arrays, providing fast random access and fast traversal. ArrayList and Vector class both implement the List interface.

  • Synchronization – ArrayList is not thread-safe whereas Vector is thread-safe. In Vector class each method like add(), get(int i) is surrounded with a synchronized block and thus making Vector class thread-safe.
  • Data growth – Internally, both the ArrayList and Vector hold onto their contents using an Array. When an element is inserted into an ArrayList or a Vector, the object will need to expand its internal array if it runs out of room. A Vector defaults to doubling the size of its array, while the ArrayList increases its array size by 50 percent.

How to Serialize a collection in java? How to serialize a ArrayList, Hashmap or Hashset object in Java

All standard implementations of collections List, Set and Map interface already implement java.io.Serializable. All the commonly used collection classes like java.util.ArrayList, java.util.Vector, java.util.Hashmap, java.util.Hashtable, java.util.HashSet, java.util.TreeSet do implement Serializable. This means you do not really need to write anything specific to serialize collection objects. However you should keep following things in mind before you serialize a collection object – Make sure all the objects added in collection are Serializable. – Serializing the collection can be costly therefore make sure you serialize only required data isntead of serializing the whole collection. – In case you are using a custom implementation of Collection interface then you may need to implement serialization for it.

Can we implement an interface in a JSP

No

What are the types of statements in JDBC

the JDBC API has 3 Interfaces, (1. Statement, 2. PreparedStatement, 3. CallableStatement ). The key features of these are as follows: Statement

  • This interface is used for executing a static SQL statement and returning the results it produces.
  • The object of Statement class can be created using Connection.createStatement() method.
  • PreparedStatement
  • A SQL statement is pre-compiled and stored in a PreparedStatement object.
  • This object can then be used to efficiently execute this statement multiple times.
  • The object of PreparedStatement class can be created using Connection.prepareStatement() method. This extends Statement interface.
  • CallableStatement
  • This interface is used to execute SQL stored procedures.
  • This extends PreparedStatement interface.
  • The object of CallableStatement class can be created using Connection.prepareCall() method.

Statement: to be used createStatement() method for executing single SQL statement

PreparedStatement: To be used preparedStatement() method for executing same SQL statement over and over.

CallableStatement: To be used prepareCall() method for multiple SQL statements over and over.

How will you configure Hibernate

The configuration files hibernate.cfg.xml (or hibernate.properties) and mapping files *.hbm.xml are used by the Configuration class to create (i.e. configure and bootstraphibernate) the SessionFactory, which in turn creates the Session instances. Session instances are the primary interface for the persistence service.hibernate.cfg.xml (alternatively can use hibernate.properties): These two files are used to configure the hibernate sevice (connection driver class, connection URL,connection username, connection password, dialect etc). If both files are present in the classpath then hibernate.cfg.xml file overrides the settings found in the hibernate.properties file.Mapping files (*.hbm.xml): These files are used to map persistent objects to a relational database. It is the best practice to store each object in an individual mapping file (i.e mapping file per class) because storing large number of persistent classes into one mapping file can be difficult to manage and maintain. The naming convention is to use the same name as the persistent (POJO) class name.

For example Account.class will have a mapping file named Account.hbm.xml. Alternatively, hibernate annotations can be used as part of your persistent class code instead of the *.hbm.xml files.