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Explain the difference between Java and JavaScript.
Explain how to obtain a performance profile of my Java Program.
Explain the purpose of the executable files that have an extra _g
at the end of their names, e.g. java_g.
If Java is platform independent, why doesn't it run on all
platforms?
Explain how to access native operating system calls from my Java
program.
How do we create and use sockets in Java?
Explain how to send data from my Java program to a CGI program.
Explain the difference between a URL instance and a URLConnection
instance.
How do I read a line of input at a time in Java?
Why is thread synchronization important for multithreaded
programs?
Explain how to create a thread and start it running.
When should we use an event adapter class?
Explain the component and container classes.
What is the difference between a runtime exception and a plain
exception?
Can you explain in brief life cycle for stateless and stateful
beans?
What is Passivation and Activation in EJB?
How do we implement caching in JSP?
Explain the different Authentication options available in
Servlets.
How can we use beans in JSP?
Explain the difference between JavaBeans and taglib directives.
Explain the different scopes an object can have in a JSP page.
Explain the use of Externalization interface.
Explain widening conversion and Narrowing conversion.
How do we implement deep cloning?
Explain the difference between StringBuilder and StringBuffer
class.
What is a StringBuffer class and how does it differ from String
Class?
What is MAP and SortedMap interface?
Difference between static and dynamic class loading.
What is Bootstrap,Extension and System Class Loader?
Can you explain the directory structure for a Struts folder in
brief?
What are action and action form classes in Struts?
How does the native language C or C++ understand data types in
JAVA?
Explain Exception handling in JNI.
What are the advantages and disadvantages of using JNI?
Explain the difference between ServletsContext and
ServletConfig.
Why is HTTP protocol called as a stateless protocol?
Can you explain the relation
between class and object? Explain with an example
What is the difference between throw
and throws clause, explain programmatically
What is meant by Tomcat in java and its
usage?
Difference between Tomcat and
Weblogic server.
What is an interface and how
will you go about implementing an interface?
Explain the difference
between Static and Non-Static fields of a class.
What are Class loaders? Explain the
types of class loader, i.e. Bootstrap Class loader, Extension Class loader and
System Class loader
Can you explain how can we practically do
dynamic loading?
Explain how to implement
Shallow Cloning.
Explain how to implement Deep
Cloning.
Can you explain how
Scheduling and Priority works in threads?
Explain how to implement
single threaded model in servlets.
Can you explain how Java
interacts with database?
Explain the different section
of JDBC and their usage.
Can you explain SQLException
class? What is SQL State in SQL Exception
Can you explain CallableStatement
interface in details?
Explain how to
do batch updates using CallableStatement interface.
Explain the architecture of a
Servet package.
Explain different
Authentication Options available in Servets.
Can you explain JDBCRealm?
Java interview questions and answers for freshers and experienced
Simple, Object-Oriented, Robust, Distributed, Portable, Interpreted,
Multithreaded, Platform Independent, Secure...........
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What is JVM? Explain its roles and functions.
Explain why Java is called as Platform independent language. Explain how Java
executable executes on any platform where JVM is available...................
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Java programming language, Java class file format, Java Application Programming
Interface, Java virtual machine.............
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Explain the features of Java class. Explain Fields, Methods, and Access Levels.
What are accessors and mutator methods in a Java class? Explain with example
for each.
Explain the importance of 'this' reference. Write a code to depicts the use of
'this' reference
Explain static variables and static methods in Java. Provide an example to
explain them..................
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What is a constructor? Explain the differences between methods and constructor.
Differences between constructors and methods.
Write code to depict the use of constructor.....................
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What is instance members? Explain with an example
What is instance variable? Explain with an example
What is instance method? Explain with an example
What is static member? Explain with an example
What is static variable? Explain with an example......................
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What are Java packages? Explain the importance of Java packages.
Steps for creating a package in Java
Explain the packages access specifier, i.e. private, protected, public,
default.............
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Explain Java Garbage collector. Why garbage collection? Brief explanation of
Garbage collection algorithms.
Explain the importance of finalizers in Java. Write code to depict the uses of
finalizers in Java...............
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Explain the importance of 'super' keyword in Java. Write code to depict the uses
of 'super' keyword - The keyword ‘super’ is used for referring parent class
instance....................
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Define Method overloading. Explain its uses. Provide a code sample to explain
the uses of Method overloading
Define Method overriding. Explain its uses. Provide a code sample to explain
the uses of Method overloading
Difference between overloading and overriding.......................
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answer
Describe Java string class. Explain methods of Java string class. Explain the
characteristics of StringBuffer class - String Class: The String class is
immutable, The contents of the String object can not be changed, String class
is final class. That implies it can not have sub classes......................
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What is Java inner class? Explain the types of inner classes, i.e. Static member
classes, Member classes, Local classes, Anonymous classes
Need of inner class in context with adapter classes
Explain few Wrapper Classes Methods...............
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Explain about Java reflection class.
Write a code sample to depict the uses of Java reflection class.........
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What is Swing? Explain the need of Swing.
Write some important features of Swing.
Describe Java Swing class hierarchy.
Explain the need of Layout manager...........
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Explain different layout manager in Java. - A layout manager organizes the
objects in a container, Different layouts are used to organize or to arrange
objects.............
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Explain the need of Exception handling.
Explain the Exceptions categories, i.e. checked and unchecked exceptions.
Provide the general form of Exception handling constructs with explanation
What is user defined Exception? Explain with an example............
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What is Multithreading? Explain the life cycle of a thread.
Explain how to use thread class for Multithreading in Java. Explain with an
example.
What is Runnable interface? Explain how to use Runnable interface for
Multithreading.
What are the methods of thread class in java? Explain them
Can your explain thread priorities?..............
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Explain the use of Streams.
Difference between Stream classes and Reader writer classes
Explain and demonstrate the use of File, RandomAccessFile classes.
Explain the use of Reader and Writer classes..............
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What is object Serialization? Explain the use of Persisting object.
Depict the step of using object Deserialization.....................
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What is socket? Explain the features of socket.
Explain the characteristics of Java socket class.
Explain ServerSocket class with an example
Explain InetAddress class with an example
Explain DatagramSocket class with an example
Explain DatagramPacket class with an example.............
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Purposes of JDBC API
Describe 4 types of JDBC drivers and their characteristics with usages.
State the functionalities of important classes in JDBC packages.
Explain how to use JDBC statement to execute SQL queries. Show in an example
Explain how to use Prepared Statement to execute parameterized queries. Show in
an example
What is JDBC Callable Statement?
What is batch updates in JDBC? Explain with an example......................
Read answer
Java interview questions and answers - April 18, 2011
What is an abstract method?
An abstract method is a method which doesn’t have a body, just declared with
modifier abstract.
Explain the use of the finally block.
Finally block is a block which always executes. The block executes even when an
exception is occurred. The block won't execute only when the user calls
System.exit()
What is the initial state of a thread?
It is in a ready state.
What is time slicing?
In time slicing, the task continues its execution for a predefined period of
time and reenters the pool of ready tasks.
What are Wrapper Classes?
Wrapper Classes allow to access primitives as objects.
What is List interface?
List is an ordered collection of objects.
Can you explain transient variables in java?
They are the variables that cannot be serialized.
What is synchronization?
Synchronization ensures only one thread to access a shared resource, thus
controls the access of multiple threads to shared resources.
What is serialization?
Serialization helps to convert the state of an object into a byte stream.
What is HashMap and Map?
Map is Interface and Hashmap is class that implements that.
Java interview questions and answers - April 18, 2011
Explain the usage of serialization.
Objects are serialized when need to be sent over network.
They are serialized when the state of an object is to be saved.
How are Observer and Observable used?
The observable class represents an observable object.
The object to be observed can be represented by sub-classing observable class.
When there is a change in an observable instance, an application calling the
Observable's notifyObservers method causes all of its observers to be notified
of the change by a call to their update method.
Difference between Swing and Awt.
AWT are heavy-weight components. Swings are light-weight components. Thus, swing
works faster than AWT.
Define inner class in Java
Class that is nested within a class is called as inner class. The inner class
can access private members of the outer class. It is mainly used to implement
data structure and some time called as a helper class.
Differences between constructors and methods.
A constructor is used to create objects of a class. A method is an ordinary
member in a class.
Constructor does not have a return type. A method should have a return type.
Constructor name is the name of the class. A method name should not be the name
of the class
Constructor is invoked at the time of creation of the class. Method needs to be
invoked in another method by using the dot operator.
Constructor can not have ‘return’ statement. All methods that return non-void
return type should have ‘return’ statement.
Define Method overriding. Explain its uses.
Method overriding is the process of writing functionality for methods with same
signature and return type, both in super class and subclass The uses of method
overriding:
Time to invest method signature is reduced
Different functionality in both super class and sub class by sharing same
signature
The functionality can be enhanced
The behavior can be replaced in the sub class
What is the purpose of the File class?
The File class provides access to the files and directories of a local file
system.
Java interview questions and answers - April 20, 2011
What is StringBuffer class?
StringBuffer class is same as String class with the exception that it is
mutable. It allows change and doesn’t create a new instance on change of value.
How can you force garbage collection?
It is not possible to force GC. We can just request it by calling System.gc().
Is it possible an exception to be rethrown?
Yes, an exception can be rethrown.
What is the return type of a program’s main() method?
A program’s main() method has a void return type.
Which package is always imported by default?
The java.lang package is always imported by default.
What is a Class?
A class implements the behavior of member objects by describing all the
attributes of objects and the methods.
What is an Object?
An object is the members of a class. It is the basic unit of a system. It has
attributes, behavior and identity.
Explain the use of "instanceOf" keyword.
"instanceOf" keyword is used to check the type of object.
How do you refer to a current instance of object?
You can refer the current instance of object using "this" keyword.
What is the use of JAVAP tool?
JAVAP is used to disassemble compiled Java files. This option is useful when
original source code is not available.
In which package is the applet class located?
Applet classes are located in "java.applet" package.
Java array vs. ArrayList class.
ArrayList is a dynamic array that can grow depending on demand whereas Java
arrays are fixed length.
Explain Enumeration Interface.
It defines the methods using which we can enumerate the elements in a collection
of objects.
What are access modifiers?
Access modifiers determine if a method or a data variable can be accessed by
another method in another class.
Explain the impact of private constructor.
Private constructor prevents a class from being explicitly instantiated by
callers.
What is an exception?
An exception is an abnormal condition that arises in a code sequence at run time
Java interview questions and answers - April 21, 2011
What are ways to create threads?
There are two ways to create a thread:
extend the java.lang.Thread class
implement the java.lang.Runnable interface
How can we stop a thread programmatically?
thread.stop;
What are daemon threads?
Daemon threads are designed to run in background. An example of such thread is
garbage collector thread.
What are the different types of locks in JDBC?
There are four types of major locks in JDBC:
Exclusive locks
Shared locks
Read locks
Update locks
What are Servlets?
Servlets are program that run under web server environments.
What are the different ways to maintain state between requests?
There are four different ways:
URL rewriting
Cookies
Hidden fields
Sessions
What are wrapper classes?
In Java we have classes for each primitive data types. These classes are called
as wrapper class. For example, Integer, Character, Double etc.
What are checked exceptions?
There are exceptions that are forced to catch by Java compiler, e.g IOException.
Those exceptions are called checked exceptions.
What is the Locale class?
Locale class is a class that converts the program output to a particular
geographic, political, or cultural region
Is main a keyword in Java?
No, main is not a keyword in Java.
What is the most important feature of Java?
Platform independency makes Java a premium language.
What is a JVM?
JVM is Java Virtual Machine which is a run time environment for the compiled
java class files.
Does Java support multiple inheritances?
No, Java doesn't support multiple inheritances.
What is the base class of all classes?
java.lang.Object
Can a class be declared as protected?
A class can't be declared as protected. Only methods can be declared as
protected.
Can an abstract class be declared final?
No, since it is obvious that an abstract class without being inherited is of no
use.
Java interview questions and answers - April 22, 2011
Can we declare a variable as abstract?
Variables can't be declared as abstract. Only classes and methods can be
declared as abstract.
Define Marker Interface.
An Interface which doesn't have any declaration inside but still enforces a
mechanism.
What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass.
When can an object reference be cast to an interface reference?
An object reference is cast to an interface reference when the object implements
the referenced interface.
Which class is extended by all other classes?
The Object class is extended by all other classes.
What is the return type of a program's main() method?
void.
What are the eight primitive Java types?
The eight primitive types are byte, char, short, int, long, float, double, and
boolean.
Difference between a public and a non-public class.
A public class may be accessed outside of its package. A non-public class may
not be accessed outside of its package.
Which Java operator is right associative?
The = operator is right associative.
What is a transient variable?
Transient variable is a variable that may not be serialized.
Java interview questions - July 07, 2011
Can you explain Native methods in Java?
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The Java native method is used to merge the power of C or C++ programming into
Java.
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To enhance to high performance language, when efficient native Java compilers
are not fully implemented, use of native method boosts the performance to at
least the speed of C compiled code.
Java applications can call code written in C, C++, or assembler. This is
sometimes done for performance and sometimes to access the underlying host
operating system or GUI API using the JNI.
Explain class loaders in Java with an example.
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The class loader describes the behavior of converting a named class into the
bits responsible for implementing that class.
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Class loaders eradicate the JREs need to know anything about files and file
systems when running Java programs.
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A class loader creates a flat name space of class bodies that are referenced by
a string name and are written as:
Class r = loadClass(String className, boolean resolveIt);
What is Reflection API in Java?
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The Reflection API allows Java code to examine classes and objects at run time.
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The new reflection classes allow you to call another class's methods
dynamically at run time.
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With the reflection classes, you can also examine an instance's fields and
change the fields' contents.
-
It is also possible to instantiate new objects, invoke methods and get/set
field values using reflection.
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The Reflection API consists of the java.lang.Class class and the
java.lang.reflect classes: Field, Method, Constructor, Array, and Modifier.
Java interview questions - July 9, 2011
Static class loading vs. dynamic class loading.
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The static class loading is done through the new operator.
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Dynamic class loading is achieved through Run time type identification. Also
called as reflection
This is done with the help of the following methods:
getClass(); getName(); getDeclaredFields();
Instance can also be created using forName() method. It loads the class into
the current class memory.
Can you explain shallow cloning and deep cloning?
Cloning of objects can be very useful if you use the prototype pattern or if you
want to store an internal copy of an object inside an aggregation class for
example.
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Deep cloning - You clone the object and their constituent parts.
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It should be used when it is inappropriate to separate the parts; the object is
formed of, from it.
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Shallow cloning - You clone only the object, not their parts. You add
references to their parts.
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It should be used when it is adequate to have the references added to the
cloned object
Explain the purpose of Comparator Interface.
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Comparators can be used to control the order of certain data structures and
collection of objects too.
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The interface can be found in java.util.Comparator
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A Comparator must define a compare function which takes two Objects and returns
a -1, 0, or 1
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Sorting can be done implicitly by using data structures of by implementing sort
methods explicitly.
Java interview questions - July 11, 2011
What is the impact of private constructor?
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Private Constructors can't be access from any derived classes neither from
another class.
-
So you have to provide a public function that calls the private constructor if
the object has not been initialized, or you have to return an instance to the
object, if it was initialized.
This can be useful for objects that can't be instantiated.
Can you explain static Initializers in Java?
A static initializer block resembles a method with no name, no arguments, and no
return type. There is no need to refer to it from outside the class definition.
Syntax:
static
{
//CODE
}
The code in a static initializer block is executed by the virtual machine when
the class is loaded.
Because it is executed automatically when the class is loaded, parameters don't
make any sense, so a static initializer block doesn't have an argument list.
Java interview questions - July 12, 2011
Define Externalizable Interface and explain its purpose.
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The Externizable interface extends the serializable interface.
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When you use Serializable interface, your class is serialized automatically by
default. But you can override writeObject() and readObject()two methods to
control more complex object serailization process.
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When you use Externalizable interface, you have a complete control over your
class's serialization process. The two methods to be implemented are : void
readExternal(ObjectInput)
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The object implements the readExternal method to restore its contents by
calling the methods of DataInput for primitive types and readObject for
objects, strings and arrays.
void writeExternal(ObjectOutput)
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The object implements the writeExternal method to save its contents by calling
the methods of DataOutput for its primitive values or calling the writeObject
method of ObjectOutput for objects, strings, and arrays.
Explain in brief transient modifiers and volatile modifiers.
When serializable interface is declared, the compiler knows that the object has
to be handled so as so be able to serialize it. However, if you declare a
variable in an object as transient, then it doesn’t get serialized.
Volatile - Specifying a variable as volatile tells the JVM that any threads
using that variable are not allowed to cache that value at all.
Volatile modifier tells the compiler that the variable modified by volatile can
be changed unexpectedly by other parts of the program.
Java interview questions - July 13, 2011
Define daemon threads and explain its purposes.
Threads that work in the background to support the runtime environment are
called daemon threads.
Eg garbage collector threads.
When the only remaining threads in a process are daemon threads, the interpreter
exits. This makes sense because when only daemon threads remain, there is no
other thread for which a daemon thread can provide a service.
You cannot create a daemon method but you can use
public final void setDaemon(boolean isDaemon) method to turn it into one.
Can you explain JAVAdoc utility.
Javadoc utility enables you to keep the code and the documentation in sync
easily.
The javadoc utility lets you put your comments right next to your code, inside
your ".java" source files.
All you need to do after completing your code is to run the Javadoc utility to
create your HTML documentation automatically.
StringBuilder class vs. StringBuffer class.
StringBuilder is unsynchronized whereas StringBuffer is synchronized. So when
the application needs to be run only in a single thread then it is better to
use StringBuilder.
StringBuilder is more efficient than StringBuffer.
Java interview questions - July 14, 2011
Can you explain semaphore and monitors in java threading?
A semaphore is a flag variable used to check whether a resource is currently
being used by another thread or process.
The drawback of semaphores is that there is no control or guarantee of proper
usage.
A Monitor defines a lock and condition variables for managing concurrent access
to shared data. The monitor uses the lock to ensure that only a single thread
is active in the monitor code at any time.
A semaphore is a generalization of a monitor. A monitor allows only one thread
to lock an object at once.
Describe synchronization in respect to multithreading.
Multithreading occurs asynchronously, meaning one thread executes independently
of the other threads. In this way, threads don’t depend on each other’s
execution. In contrast, processes that run synchronously depend on each other.
That is, one process waits until the other process terminates before it can
execute
Java interview questions - July 15, 2011
What are Checked and UnChecked Exception?
The java.lang.Throwable class has two subclasses Error and Exception. There are
two types of exceptions non runtime exceptions and runtime exceptions. Non
runtime exceptions are called checked exceptions and the unchecked exceptions
are runtime exceptions.
Runtime Exceptions occur when the code is not robust and non runtime exceptions
occur due to the problems is environment, settings, etc.
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