Java Interview Questions and Answers
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Which containers use a
Border layout as their default layout?-
Window, Frame and Dialog classes use a BorderLayout as their layout.
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Which containers use a
Flow layout as their default layout?-
Panel and Applet classes use the FlowLayout as their default layout.
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What are wrapper
classes?-
Wrapper classes are classes that allow primitive types to be accessed as
objects.
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What are Vector,
Hashtable, LinkedList and Enumeration?-
Vector : The Vector class provides the capability to implement a growable array
of objects. Hashtable : The Hashtable class implements a Hashtable data
structure. A Hashtable indexes and stores objects in a dictionary using hash
codes as the object’s keys. Hash codes are integer values that identify
objects. LinkedList: Removing or inserting elements in the middle of an array
can be done using LinkedList. A LinkedList stores each object in a separate
link whereas an array stores object references in consecutive locations.
Enumeration: An object that implements the Enumeration interface generates a
series of elements, one at a time. It has two methods, namely hasMoreElements()
and nextElement(). HasMoreElemnts() tests if this enumeration has more elements
and nextElement method returns successive elements of the series.
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What is the difference
between set and list?-
Set stores elements in an unordered way but does not contain duplicate
elements, whereas list stores elements in an ordered way but may contain
duplicate elements.
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What is a stream and
what are the types of Streams and classes of the Streams?-
A Stream is an abstraction that either produces or consumes information. There
are two types of Streams and they are: Byte Streams: Provide a convenient means
for handling input and output of bytes. Character Streams: Provide a convenient
means for handling input & output of characters. Byte Streams classes: Are
defined by using two abstract classes, namely InputStream and OutputStream.
Character Streams classes: Are defined by using two abstract classes, namely
Reader and Writer.
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What is the difference
between Reader/Writer and InputStream/Output Stream?-
The Reader/Writer class is character-oriented and the InputStream/OutputStream
class is byte-oriented.
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What is an I/O filter?-
An I/O filter is an object that reads from one stream and writes to another,
usually altering the data in some way as it is passed from one stream to
another.
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What is serialization
and deserialization?-
Serialization is the process of writing the state of an object to a byte
stream. Deserialization is the process of restoring these objects.
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What is JDBC?-
JDBC is a set of Java API for executing SQL statements. This API consists of a
set of classes and interfaces to enable programs to write pure Java Database
applications.
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What are drivers
available?-
a) JDBC-ODBC Bridge driver b) Native API Partly-Java driver c) JDBC-Net Pure
Java driver d) Native-Protocol Pure Java driver
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What is the difference
between JDBC and ODBC?-
a) OBDC is for Microsoft and JDBC is for Java applications. b) ODBC can’t be
directly used with Java because it uses a C interface. c) ODBC makes use of
pointers which have been removed totally from Java. d) ODBC mixes simple and
advanced features together and has complex options for simple queries. But JDBC
is designed to keep things simple while allowing advanced capabilities when
required. e) ODBC requires manual installation of the ODBC driver manager and
driver on all client machines. JDBC drivers are written in Java and JDBC code
is automatically installable, secure, and portable on all platforms. f) JDBC
API is a natural Java interface and is built on ODBC. JDBC retains some of the
basic features of ODBC.
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What are the types of
JDBC Driver Models and explain them?-
There are two types of JDBC Driver Models and they are: a) Two tier model and
b) Three tier model Two tier model: In this model, Java applications interact
directly with the database. A JDBC driver is required to communicate with the
particular database management system that is being accessed. SQL statements
are sent to the database and the results are given to user. This model is
referred to as client/server configuration where user is the client and the
machine that has the database is called as the server. Three tier model: A
middle tier is introduced in this model. The functions of this model are: a)
Collection of SQL statements from the client and handing it over to the
database, b) Receiving results from database to the client and c) Maintaining
control over accessing and updating of the above.
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What are the steps
involved for making a connection with a database or how do you connect to a
database?a)
Loading the driver : To load the driver, Class. forName() method is used.
Class. forName(”sun. jdbc. odbc. JdbcOdbcDriver”); When the driver is loaded,
it registers itself with the java. sql. DriverManager class as an available
database driver. b) Making a connection with database: To open a connection to
a given database, DriverManager. getConnection() method is used. Connection con
= DriverManager. getConnection (”jdbc:odbc:somedb”, “user”, “password”); c)
Executing SQL statements : To execute a SQL query, java. sql. statements class
is used. createStatement() method of Connection to obtain a new Statement
object. Statement stmt = con. createStatement(); A query that returns data can
be executed using the executeQuery() method of Statement. This method executes
the statement and returns a java. sql. ResultSet that encapsulates the
retrieved data: ResultSet rs = stmt. executeQuery(”SELECT * FROM some table”);
d) Process the results : ResultSet returns one row at a time. Next() method of
ResultSet object can be called to move to the next row. The getString() and
getObject() methods are used for retrieving column values: while(rs. next()) {
String event = rs. getString(”event”); Object count = (Integer) rs.
getObject(”count”);
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What type of driver did
you use in project?-
JDBC-
ODBC
Bridge
driver (is a driver that uses native(C language) libraries and makes calls to
an existing ODBC driver to access a database engine).
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