Core Java: Basics of Java
Interview Questions
1) What
is difference between JDK,JRE and JVM?
2) How
many types of memory areas are allocated by JVM?
- Class(Method)
Area
- Heap
- Stack
- Program
Counter Register
- Native
Method Stack
3) What
is JIT compiler?
4) What
is platform?
5) What
is the main difference between Java platform and other platforms?
- Runtime
Environment
- API(Application
Programming Interface)
6) What gives
Java its 'write once and run anywhere' nature?
7) What
is classloader?
8) Is
Empty .java file name a valid source file name?
9) Is
delete,next,main,exit or null keyword in java?
10) If I
don't provide any arguments on the command line, then the String array of Main
method will be empty or null?
11) What
if I write static public void instead of public static void?
12) What
is the default value of the local variables?
Core Java - OOPs Concepts:
Initial OOPs Interview Questions
13) What
is difference between object oriented programming language and object based
programming language?
Core Java - OOPs Concepts:
Constructor Interview Questions
15) What
is constructor?
- Constructor is just like a
method that is used to initialize the state of an object. It is invoked at
the time of object creation.
16) What
is the purpose of default constructor?
- The default constructor provides
the default values to the objects. The java compiler creates a default
constructor only if there is no constructor in the class.
17) Does
constructor return any value?
18)Is
constructor inherited?
19) Can
you make a constructor final?
Core Java - OOPs Concepts: static
keyword Interview Questions
20) What
is static variable?
- static
variable is used to refer the common property of all objects (that is not
unique for each object) e.g. company name of employees,college name of
students etc.
- static
variable gets memory only once in class area at the time of class loading.
21) What
is static method?
- A
static method belongs to the class rather than object of a class.
- A
static method can be invoked without the need for creating an instance of
a class.
- static
method can access static data member and can change the value of it.
22) Why
main method is static?
23) What
is static block?
- Is used
to initialize the static data member.
- It is
excuted before main method at the time of classloading.
24) Can
we execute a program without main() method?
25) What
if the static modifier is removed from the signature of the main method?
26) What
is difference between static (class) method and instance method?
static
or class method
|
instance
method
|
1)A method i.e. declared as static is known as static method.
|
A method i.e. not declared as static is known as instance method.
|
2)Object is not required to call static method.
|
Object is required to call instance methods.
|
3)Non-static (instance) members cannot be accessed in static context
(static method, static block and static nested class) directly.
|
static and non-static variables both can be accessed in instance
methods.
|
4)For example: public static int cube(int n){ return n*n*n;}
|
For example: public void msg(){...}.
|
Core Java - OOPs Concepts:
Inheritance Interview Questions
27) What
is this in java?
28)What
is Inheritance?
Inheritance
is a mechanism in which one object acquires all the properties and behaviour of
another object of another class. It represents IS-A relationship. It is used
for Code Resusability and Method Overriding.
29) Which
class is the superclass for every class.
Object
class.
30) Why
multiple inheritance is not supported in java?
- To reduce the complexity and
simplify the language, multiple inheritance is not supported in java in
case of class.
31) What
is composition?
Holding the
reference of the other class within some other class is known as composition.
32) What
is difference between aggregation and composition?
Aggregation
represents weak relationship whereas composition represents strong
relationship. For example: bike has an indicator (aggregation) but bike has an
engine (compostion).
33) Why
Java does not support pointers?
Pointer is a
variable that refers to the memory address. They are not used in java because
they are unsafe(unsecured) and complex to understand.
34) What
is super in java?
35) Can
you use this() and super() both in a constructor?
No. Because
super() or this() must be the first statement.
36)What
is object cloning?
Core Java - OOPs Concepts: Method
Overloading Interview Questions
37) What
is method overloading?
If a class
have multiple methods by same name but different parameters, it is known as
Method Overloading. It increases the readability of the program.
38) Why
method overloading is not possible by changing the return type in java?
39) Can
we overload main() method?
Yes, You can
have many main() methods in a class by overloading the main method.
Core Java - OOPs Concepts: Method
Overriding Interview Questions
40) What
is method overriding:
If a
subclass provides a specific implementation of a method that is already
provided by its parent class, it is known as Method Overriding. It is used for
runtime polymorphism and to provide the specific implementation of the method.
41) Can
we override static method?
No, you
can't override the static method because they are the part of class not object.
42) Why
we cannot override static method?
It is
because the static method is the part of class and it is bound with class
whereas instance method is bound with object and static gets memory in class
area and instance gets memory in heap.
43) Can
we override the overloaded method?
Yes.
44)
Difference between method Overloading and Overriding.
Method
Overloading
|
Method
Overriding
|
1) Method overloading increases the readability of the program.
|
Method overriding provides the specific implementation of the method
that is already provided by its super class.
|
2) method overlaoding is occurs within the class.
|
Method overriding occurs in two classes that have IS-A relationship.
|
3) In this case, parameter must be different.
|
In this case, parameter must be same.
|
45) Can
you have virtual functions in Java?
Yes, all
functions in Java are virtual by default.
46) What
is covariant return type?
Now, since
java5, it is possible to override any method by changing the return type if the
return type of the subclass overriding method is subclass type. It is known as
covariant return type.
Core Java - OOPs Concepts: final
keyword Interview Questions
47) What
is final variable?
If you make
any variable as final, you cannot change the value of final variable(It will be
constant).
48) What
is final method?
49) What
is final class?
50) What
is blank final variable?
51) Can
we intialize blank final variable?
Yes, only in
constructor if it is non-static. If it is static blank final variable, it can
be initialized only in the static block.
52) Can
you declare the main method as final?
Yes, such
as, public static final void main(String[] args){}.
Core Java - OOPs : Polymorphism
Interview Questions
53) What
is Runtime Polymorphism?
Runtime
polymorphism or dynamic method dispatch is a process in which a call to an
overridden method is resolved at runtime rather than at compile-time.
In this
process, an overridden method is called through the reference variable of a
super class. The determination of the method to be called is based on the
object being referred to by the reference variable.
54) Can
you achieve Runtime Polymorphism by data members?
No.
55) What
is the difference between static binding and dynamic binding?
In case of
static binding type of object is determined at compile time whereas in dynamic
binding type of object is determined at runtime.
Core Java - OOPs Concepts :
Abstraction Interview Questions
56) What
is abstraction?
Abstraction
is a process of hiding the implementation details and showing only
functionality to the user.
Abstraction
lets you focus on what the object does instead of how it does it.
57) What
is the difference between abstraction and encapsulation?
Abstraction
hides the implementation details whereas encapsulation wraps code and data into
a single unit.
58) What
is abstract class?
A class that
is declared as abstract is known as abstract class. It needs to be extended and
its method implemented. It cannot be instantiated.
59) Can
there be any abstract method without abstract class?
No, if there
is any abstract method in a class, that class must be abstract.
60) Can
you use abstract and final both with a method?
No, because
abstract method needs to be overridden whereas you can't override final method.
61) Is it
possible to instantiate the abstract class?
No, abstract
class can never be instantiated.
62) What
is interface?
Interface is
a blueprint of a class that have static constants and abstract methods.It can
be used to achieve fully abstraction and multiple inheritance.
63) Can
you declare an interface method static?
No, because
methods of an interface is abstract by default, and static and abstract
keywords can't be used together.
64) Can
an Interface be final?
No, because
its implementation is provided by another class.
65) What
is marker interface?
An interface
that have no data member and method is known as a marker interface.For example
Serializable, Cloneable etc.
66) What
is difference between abstract class and interface?
Abstract
class
|
Interface
|
1)An abstract class can have method body (non-abstract methods).
|
Interface have only abstract methods.
|
2)An abstract class can have instance variables.
|
An interface cannot have instance variables.
|
3)An abstract class can have constructor.
|
Interface cannot have constructor.
|
4)An abstract class can have static methods.
|
Interface cannot have static methods.
|
5)You can extends one abstract class.
|
You can implement multiple interfaces.
|
67) Can
we define private and protected modifiers for variables in interfaces?
No, they are
implicitly public.
68) When
can an object reference be cast to an interface reference?
An object
reference can be cast to an interface reference when the object implements the
referenced interface.
Core Java - OOPs Concepts :
Package Interview Questions
69) What
is package?
A package is
a group of similar type of classes interfaces and sub-packages. It provides
access protection and removes naming collision.
70) Do I
need to import java.lang package any time? Why ?
No. It is by
default loaded internally by the JVM.
71) Can I
import same package/class twice? Will the JVM load the package twice at
runtime?
One can
import the same package or same class multiple times. Neither compiler nor JVM
complains about it.But the JVM will internally load the class only once no
matter how many times you import the same class.
72) What
is static import ?
By static
import, we can access the static members of a class directly, there is no to
qualify it with the class name.
Java : Exception Handling
Interview Questions
There is
given a list of exception handling interview questions with answers. If you
know any exception handling interview question, kindly post it in the comment
section.
73) What
is Exception Handling?
Exception
Handling is a mechanism to handle runtime errors.It is mainly used to handle
checked exceptions.
74) What
is difference between Checked Exception and Unchecked Exception?
1)Checked
Exception
The classes
that extend Throwable class except RuntimeException and Error are known as
checked exceptions e.g.IOException,SQLException etc. Checked exceptions are
checked at compile-time.
2)Unchecked
Exception
The classes
that extend RuntimeException are known as unchecked exceptions e.g.
ArithmeticException,NullPointerException etc. Unchecked exceptions are not
checked at compile-time.
75) What
is the base class for Error and Exception?
Throwable.
76) Is it
necessary that each try block must be followed by a catch block?
It is not
necessary that each try block must be followed by a catch block. It should be
followed by either a catch block OR a finally block. And whatever exceptions
are likely to be thrown should be declared in the throws clause of the method.
77) What
is finally block?
78) Can
finally block be used without catch?
79) Is
there any case when finally will not be executed?
finally
block will not be executed if program exits(either by calling System.exit() or
by causing a fatal error that causes the process to abort).
80) What
is difference between throw and throws?
throw
keyword
|
throws
keyword
|
1)throw is used to explicitly throw an exception.
|
throws is used to declare an exception.
|
2)checked exceptions can not be propagated with throw only.
|
checked exception can be propagated with throws.
|
3)throw is followed by an instance.
|
throws is followed by class.
|
4)throw is used within the method.
|
throws is used with the method signature.
|
5)You cannot throw multiple exception
|
You can declare multiple exception e.g. public void method()throws
IOException,SQLException.
|
81) Can
an exception be rethrown?
Yes.
82) Can
subclass overriding method declare an exception if parent class method doesn't
throw an exception ?
Yes but only
unchecked exception not checked.
83) What
is exception propagation ?
Forwarding
the exception object to the invoking method is known as exception propagation.
Java: String Handling Interview
Questions
There is
given a list of string handling interview questions with short and pointed
answers. If you know any string handling interview question, kindly post it in
the comment section.
84) What
is the meaning of immutable in terms of String?
The simple
meaning of immutable is unmodifiable or unchangeable. Once string object has
been created, its value can't be changed.
85) Why
string objects are immutable in java?
Because java
uses the concept of string literal. Suppose there are 5 reference variables,all
referes to one object "sachin".If one reference variable changes the
value of the object, it will be affected to all the reference variables. That
is why string objects are immutable in java.
86) How
many ways we can create the string object?
There are
two ways to create the string object, by string literal and by new keyword.
87) How
many objects will be created in the following code?
1. String s1="Welcome";
2. String s2="Welcome";
3.
String s3="Welcome";
Only one
object.
88) Why
java uses the concept of string literal?
To make Java
more memory efficient (because no new objects are created if it exists already
in string constant pool).
89)How
many objects will be created in the following code?
1.
String s = new String("Welcome");
Two objects,
one in string constant pool and other in non-pool(heap).
90) What
is the basic difference between string and stringbuffer object?
String is an
immutable object. StringBuffer is a mutable object.
91) What
is the difference between StringBuffer and StringBuilder ?
StringBuffer
is synchronized whereas StringBuilder is not synchronized.
92) How
can we create immutable class in java ?
We can
create immutable class as the String class by defining final class and
93) What
is the purpose of toString() method in java ?
The
toString() method returns the string representation of any object. If you print
any object, java compiler internally invokes the toString() method on the
object. So overriding the toString() method, returns the desired output, it can
be the state of an object etc. depends on your implementation.
Core Java : Nested classes and
Interfaces Interview Questions
94)What
is nested class?
A class
which is declared inside another class is known as nested class. There are 4
types of nested class member inner class, local inner class, annonymous inner
class and static nested class.
95) Is
there any difference between nested classes and inner classes?
Yes, inner
classes are non-static nested classes i.e. inner classes are the part of nested
classes.
96) Can
we access the non-final local variable, inside the local inner class?
No, local
variable must be constant if you want to access it in local inner class.
97) What
is nested interface ?
Any
interface i.e. declared inside the interface or class, is known as nested
interface. It is static by default.
98) Can a
class have an interface?
Yes, it is
known as nested interface.
99) Can
an Interface have a class?
Yes, they
are static implicitely.
Garbage Collection Interview
Questions
117) What
is Garbage Collection?
Garbage
collection is a process of reclaiming the runtime unused objects.It is
performed for memory management.
118) What
is gc()?
gc() is a
daemon thread.gc() method is defined in System class that is used to send
request to JVM to perform garbage collection.
119) What
is the purpose of finalize() method?
finalize()
method is invoked just before the object is garbage collected.It is used to
perform cleanup processing.
120) Can
an unrefrenced objects be refrenced again?
Yes.
121)What
kind of thread is the Garbage collector thread?
Daemon
thread.
122)What
is difference between final, finally and finalize?
final: final is a keyword, final can be variable,
method or class.You, can't change the value of final variable, can't override
final method, can't inherit final class.
|
finally: finally block is used in exception
handling. finally block is always executed.
|
finalize():finalize() method is used in garbage
collection.finalize() method is invoked just before the object is garbage
collected.The finalize() method can be used to perform any cleanup
processing.
|
123)What
is the purpose of the Runtime class?
The purpose
of the Runtime class is to provide access to the Java runtime system.
124)How
will you invoke any external process in Java?
By
Runtime.getRuntime().exec(?) method.
I/O Interview Questions
125)What
is the difference between the Reader/Writer class hierarchy and the
InputStream/OutputStream class hierarchy?
The
Reader/Writer class hierarchy is character-oriented, and the
InputStream/OutputStream class hierarchy is byte-oriented.
126)What
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.
Serialization Interview Questions
127) What
is serialization?
Serialization
is a process of writing the state of an object into a byte stream.It is mainly
used to travel object's state on the network.
128) What
is Deserialization?
Deserialization
is the process of reconstructing the object from the serialized state.It is the
reverse operation of serialization.
129) What
is transient keyword?
130)What
is Externalizable?
Externalizable
interface is used to write the state of an object into a byte stream in
compressed format.It is not a marker interface.
131)What
is the difference between Serializalble and Externalizable interface?
Serializable
is a marker interface but Externalizable is not a marker interface.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. When you use Externalizable interface,
you have a complete control over your class's serialization process.
Networking Interview Questions
132)How
do I convert a numeric IP address like 192.18.97.39 into a hostname like
java.sun.com?
By
InetAddress.getByName("192.18.97.39").getHostName() where
192.18.97.39 is the IP address.
Reflection Interview Questions
133) What
is reflection?
Reflection
is the process of examining or modifying the runtime behaviour of a class at
runtime.It is used in:
- IDE
(Integreted Development Environment) e.g. Eclipse, MyEclipse, NetBeans.
- Debugger
- Test
Tools etc.
134) Can
you access the private method from outside the class?
Yes, by
changing the runtime behaviour of a class if the class is not secured.
Miscellaneous Interview Questions
148)What
are wrapper classes?
Wrapper
classes are classes that allow primitive types to be accessed as objects.
149)What
is a native method?
A native
method is a method that is implemented in a language other than Java.
150)What
is the purpose of the System class?
The purpose
of the System class is to provide access to system resources.
151)What
comes to mind when someone mentions a shallow copy in Java?
Object
cloning.
152)What
is singleton class?
Singleton
class means that any given time only one instance of the class is present, in
one JVM.
AWT and SWING Interview Questions
153)Which
containers use a border layout as their default layout?
The Window,
Frame and Dialog classes use a border layout as their default layout.
154)Which
containers use a FlowLayout as their default layout?
The Panel
and Applet classes use the FlowLayout as their default layout.
155)What
are peerless components?
The peerless
components are called light weight components.
156)is
the difference between a Scrollbar and a ScrollPane?
A Scrollbar
is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane
handles its own events and performs its own scrolling.
157)What
is a lightweight component?
Lightweight
components are the one which doesn?t go with the native call to obtain the
graphical units. They share their parent component graphical units to render
them. For example, Swing components.
158)What
is a heavyweight component?
For every
paint call, there will be a native call to get the graphical units.For Example,
AWT.
159)What
is an applet?
An applet is
a small java program that runs inside the browser and generates dynamic
contents.
160)Can
you write a Java class that could be used both as an applet as well as an
application?
Yes. Add a
main() method to the applet.
Internationalization Interview
Questions
161)What
is Locale?
A Locale
object represents a specific geographical, political, or cultural region.
162)How
will you load a specific locale?
By
ResourceBundle.getBundle(?) method.
Java Bean Interview Questions
163)What
is a JavaBean?
are reusable
software components written in the Java programming language, designed to be
manipulated visually by a software development environment, like JBuilder or
VisualAge for Java.
RMI Interview Questions
164)Can
RMI and Corba based applications interact?
Yes they
can. RMI is available with IIOP as the transport protocol instead of JRMP.
Java Multithreading Interview Questions
Multithreading
and Synchronization is considered as the typical chapter in java programming.
In game development company, mulithreading related interview questions are
asked mostly. A list of frequently asked java multithreading interview
questions are given below.
1) What
is multithreading?
Multithreading
is a process of executing multiple threads simultaneously. Its main advantage
is:
- Threads
share the same address space.
- Thread
is lightweight.
- Cost of
communication between process is low.
2) What
is thread?
A thread is
a lightweight subprocess.It is a separate path of execution.It is called
separate path of execution because each thread runs in a separate stack frame.
3)What is
the difference between preemptive scheduling and time slicing?
Under
preemptive scheduling, the highest priority task executes until it enters the
waiting or dead states or a higher priority task comes into existence. Under
time slicing, a task executes for a predefined slice of time and then reenters
the pool of ready tasks. The scheduler then determines which task should
execute next, based on priority and other factors.
4) What
does join() method?
The join()
method waits for a thread to die. In other words, it causes the currently
running threads to stop executing until the thread it joins with completes its
task.
5) What
is difference between wait() and sleep() method?
wait()
|
sleep()
|
1) The wait() method is defined in Object class.
|
The sleep() method is defined in Thread class.
|
2) wait() method releases the lock.
|
The sleep() method doesn't releases the lock.
|
6) Is it
possible to start a thread twice?
No, there is
no possibility to start a thread twice. If we does, it throws an exception.
7) Can we
call the run() method instead of start()?
yes, but it
will not work as a thread rather it will work as a normal object so there will
not be context-switching between the threads.
8) What
about the daemon threads?
The daemon
threads are basically the low priority threads that provides the background
support to the user threads. It provides services to the user threads.
9)Can we
make the user thread as daemon thread if thread is started?
No, if you
do so, it will throw IllegalThreadStateException
10)What
is shutdown hook?
The shutdown
hook is basically a thread i.e. invoked implicitely before JVM shuts down. So
we can use it perform clean up resource.
11)When
should we interrupt a thread?
We should
interrupt a thread if we want to break out the sleep or wait state of a thread.
12) What
is synchronization?
Synchronization
is the capabilility of control the access of multiple threads to any shared
resource.It is used:
- To
prevent thread interference.
- To
prevent consistency problem.
13) What
is the purpose of Synchronized block?
- Synchronized
block is used to lock an object for any shared resource.
- Scope
of synchronized block is smaller than the method.
14)Can
Java object be locked down for exclusive use by a given thread?
Yes. You can
lock an object by putting it in a "synchronized" block. The locked
object is inaccessible to any thread other than the one that explicitly claimed
it.
15) What
is static synchronization?
16)What
is the difference between notify() and notifyAll()?
The notify()
is used to unblock one waiting thread whereas notifyAll() method is used to
unblock all the threads in waiting state.
17)What
is deadlock?
Deadlock is
a situation when two threads are waiting on each other to release a resource.
Each thread waiting for a resource which is held by the other waiting thread.
Java Collections Interview Questions
In java,
collection interview questions are mostly asked by the interviewers. Here is
the list of mostly asked collections interview questions with answers.
1) What
is the difference between ArrayList and Vector?
No.
|
ArrayList
|
Vector
|
1)
|
ArrayList is not synchronized.
|
Vector is synchronized.
|
2)
|
ArrayList is not a legacy class.
|
Vector is a legacy class.
|
3)
|
ArrayList increases its size by 50% of the array size.
|
Vector increases its size by doubling the array size.
|
2) What
is the difference between ArrayList and LinkedList?
No.
|
ArrayList
|
LinkedList
|
1)
|
ArrayList uses a dynamic array.
|
LinkedList uses doubly linked list.
|
2)
|
ArrayList is not efficient for manipulation because a lot of shifting
is required.
|
LinkedList is efficient for manipulation.
|
3)
|
ArrayList is better to store and fetch data.
|
LinkedList is better to manipulate data.
|
3) What
is the difference between Iterator and ListIterator?
Iterator
traverses the elements in forward direction only whereas ListIterator traverses
the elements in forward and backward direction.
No.
|
Iterator
|
ListIterator
|
1)
|
Iterator traverses the elements in forward direction only.
|
ListIterator traverses the elements in backward and forward directions
both.
|
2)
|
Iterator can be used in List, Set and Queue.
|
ListIterator can be used in List only.
|
4) What
is the difference between Iterator and Enumeration?
No.
|
Iterator
|
Enumeration
|
1)
|
Iterator can traverse legacy and non-legacy elements.
|
Enumeration can traverse only legacy elements.
|
2)
|
Iterator is fail-fast.
|
Enumeration is not fail-fast.
|
3)
|
Iterator is slower than Enumeration.
|
Enumeration is faster than Iterator.
|
5) What
is the difference between List and Set?
List can
contain duplicate elements whereas Set contains only unique elements.
6) What
is the difference between HashSet and TreeSet?
HashSet
maintains no order whereas TreeSet maintains ascending
order.
7) What
is the difference between Set and Map?
Set contains
values only whereas Map contains key and values both.
8) What
is the difference between HashSet and HashMap?
HashSet
contains only values whereas HashMap contains entry(key,value). HashSet can be
iterated but HashMap need to convert into Set to be iterated.
9) What
is the difference between HashMap and TreeMap?
HashMap
maintains no order but TreeMap maintains ascending
order.
10) What
is the difference between HashMap and Hashtable?
No.
|
HashMap
|
Hashtable
|
1)
|
HashMap is not synchronized.
|
Hashtable is synchronized.
|
2)
|
HashMap can contain one null key and multiple null values.
|
Hashtable cannot contain any null key or null value.
|
11) What
is the difference between Collection and Collections?
Collection
is an interface whereas Collections is a class. Collection interface provides
normal functionality of data structure to List, Set and Queue. But, Collections
class is to sort and synchronize collection elements.
12) What
is the difference between Comparable and Comparator?
No.
|
Comparable
|
Comparator
|
1)
|
Comparable provides only one sort of sequence.
|
Comparator provides multiple sort of sequences.
|
2)
|
It provides one method named compareTo().
|
It provides one method named compare().
|
3)
|
It is found in java.lang package.
|
it is found in java.util package.
|
4)
|
If we implement Comparable interface, actual class is modified.
|
Actual class is not modified.
|
13) What
is the advantage of Properties file?
If you
change the value in properties file, you don't need to recompile the java
class. So, it makes the application easy to manage.
14) What
does the hashCode() method?
The
hashCode() method returns a hash code value (an integer number).
The
hashCode() method returns the same integer number, if two keys (by calling
equals() method) are same.
But, it is
possible that two hash code numbers can have different or same keys.
15) Why
we override equals() method?
The equals
method is used to check whether two objects are same or not. It needs to be
overridden if we want to check the objects based on property.
For example,
Employee is a class that has 3 data members: id, name and salary. But, we want
to check the equality of employee object on the basis of salary. Then, we need
to override the equals() method.
16) How
to synchronize List, Set and Map elements?
Yes,
Collections class provides methods to make List, Set or Map elements as
synchronized:
public static List synchronizedList(List l){}
|
public static Set synchronizedSet(Set s){}
|
public static SortedSet synchronizedSortedSet(SortedSet s){}
|
public static Map synchronizedMap(Map m){}
|
public static SortedMap synchronizedSortedMap(SortedMap m){}
|
17) What
is the advantage of generic collection?
If we use
generic class, we don't need typecasting. It is typesafe and checked at compile
time.
18) What
is hash-collision in Hashtable and how it is handled in Java?
Two
different keys with the same hash value is known as hash-collision. Two
different entries will be kept in a single hash bucket to avoid the collision.
19) What
is the Dictionary class?
The
Dictionary class provides the capability to store key-value pairs.
20) What
is the default size of load factor in hashing based collection?
The default
size of load factor is 0.75. The default capacity is computed as
initial capacity * load factor. For example, 16 * 0.75 = 12. So, 12 is the
default capacity of Map.
JDBC Interview Questions
A list of
frequently asked jdbc interview questions with answers are given below.
1) What
is JDBC?
JDBC is a
Java API that is used to connect and execute query to the database. JDBC API
uses jdbc drivers to connects to the database.
2) What
is JDBC Driver?
JDBC Driver
is a software component that enables java application to interact with the
database.There are 4 types of JDBC drivers:
- JDBC-ODBC
bridge driver
- Native-API
driver (partially java driver)
- Network
Protocol driver (fully java driver)
- Thin
driver (fully java driver)
3) What
are the steps to connect to the database in java?
- Registering
the driver class
- Creating
connection
- Creating
statement
- Executing
queries
- Closing
connection
4) What
are the JDBC API components?
The java.sql
package contains interfaces and classes for JDBC API.
Interfaces:
- Connection
- Statement
- PreparedStatement
- ResultSet
- ResultSetMetaData
- DatabaseMetaData
- CallableStatement
etc.
Classes:
- DriverManager
- Blob
- Clob
- Types
- SQLException
etc.
5) What
are the JDBC statements?
There are 3
JDBC statements.
- Statement
- PreparedStatement
- CallableStatement
6) What
is the difference between Statement and PreparedStatement interface?
In case of
Statement, query is complied each time whereas in case of PreparedStatement,
query is complied only once. So performance of PreparedStatement is better than
Statement.
7) How
can we execute stored procedures and functions?
By
using Callable statement interface, we can execute procedures
and functions.
8) What is
the role of JDBC DriverManager class?
The DriverManager
class manages the registered drivers. It can be used to register and
unregister drivers. It provides factory method that returns the instance of
Connection.
9) What
does the JDBC Connection interface?
The Connection
interface maintains a session with the database. It can be used for
transaction management. It provides factory methods that returns the instance
of Statement, PreparedStatement, CallableStatement and DatabaseMetaData.
10) What
does the JDBC ResultSet interface?
The
ResultSet object represents a row of a table. It can be used to change the
cursor pointer and get the information from the database.
11) What
does the JDBC ResultSetMetaData interface?
The
ResultSetMetaData interface returns the information of table such as total
number of columns, column name, column type etc.
12) What
does the JDBC DatabaseMetaData interface?
The
DatabaseMetaData interface returns the information of the database such as
username, driver name, driver version, number of tables, number of views etc.
13) Which
interface is responsible for transaction management in JDBC?
The Connection
interface provides methods for transaction management such as
commit(), rollback() etc.
14) What
is batch processing and how to perform batch processing in JDBC?
By using
batch processing technique in JDBC, we can execute multiple queries. It makes
the performance fast.
15) How
can we store and retrieve images from the database?
By using
PreparedStatement interface, we can store and retrieve images.
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