Java interview question for experienced and Core Java Interview Questions and Answers
Core java interview questions for experienced
Why
we preferred event-delegation model over earlier event-inheritance model?
- The event-delegation model has two
advantages over the event-inheritance model.
- Event-delegation helps in event handling by objects
other than those who generate the events.
- Help in differentiating between component design and
its use.
- Event-delegation performs much better in applications
where generation of events takes place.
- Event-delegation model does not repeatedly process
unhandled events, which cause improvement in the performance.
How
is Java source code files named?
- Java source code file takes the name
of a public class or interface that is defined by the programmer while coding
within the file. Source code file may contain maximum one public class or
interface in the file. Two cases me occur while naming of the java source code
file:
- When public class or interface is defined within a
source code file then the java source code file must take the name of the
public class or interface defined while coding.
- When no public class or interface is defined inside a
source code file, then the java source code file take a name that is
different than its classes and interfaces. Source code files use the .java
extension.
What
are the advantages of Java layout managers?
- In Java Button, Checkbox, Lists,
Scrollbars, Text Fields, and Text Area etc positioned by the default layout
manager. Using algorithm layout manager automatically arranges the controls
within a window. In Windows environment, we can control layout manually. But we
do not do it manual because of following two reasons:
- It is very tedious to manually lay out a large number
of components.
- Sometimes the width and height information is not
available when you need to arrange some control, because the native
toolkit components have not been realized. This is a chicken-and-egg
situation.
- Java uses layout managers to lay out
components in a consistent manner across all windowing platforms.
What
is the difference between a Choice and a List?
The between Choice and list are
following:
- Choice class presents a pop-up menu of choices whereas
List is a collection of different visible item.
- Choice is displayed in a compact form, to see the list
of available choices we need to scroll down whereas list displays the
entire available items.
- Choice allows selecting only one items but List
supports the selection of one or more List items.
- Lists typically allow duplicate elements selection.
List allow pairs of elements e1 and e2 such that e1.equals(e2), and they
typically allow multiple null elements if they allow null elements at all.
What
is the difference between the event model and the event-delegation model?
Difference between event model and
event-delegation are following:
- The event-delegation model eliminates the processing
required to support in the handling of unhandled events.
- Event delegation model allow components to handle their
own events. When components are unable to handle a particular event, then
event is inherited by the component container.
- In the event-delegation model, specific objects are
designated as event handlers for GUI components. These objects implement
event-listener interfaces.
- The JDK 1.02 event model uses an event inheritance
What
restrictions are placed on method overriding?
- The restrictions on method
overloading are the signature of the method.
- Signature is number, type, and order of the arguments
passed to a method.
- Overridden methods must have the same name, argument
list, and return type.
- Any method which has the same name cannot have the same
signature.
- They can have the same return types in the same scope.
- The compiler uses the signature to detect which overloaded
method to refer when an overloaded method is called.
- If two methods have the same name and signature the
compiler will throw a runtime error.
What
is numeric promotion?
- Numeric promotions are used for the
conversion of the operands of a numeric operator into a common type. This
conversation is performed so that we can easily perform the calculation on it.
- It is the conversion of a smaller numeric type to a
larger numeric type, so that integer and floating-point operations can be
performed over it.
- In this byte, char, and short values are converted to
int values.
- The int values are also converted to long values. The
long and float values are converted to double values.
Can
you compare SWING and AWT?
- Swing components operate same as AWT
components, the only differences are that Swing provides a number of new event
types.
- Few Swing components don't have an AWT counterpart.
- Swing is an extension of AWT. It is not the replacement
for the AWT.
- The advantages of Swing components is components are
not rendered on the screen by the operating system, the look and feel of a
component does not change when application is running on different
platform using different versions.
- It is possible to cause Swing components to mimic the
look and feel of a specific platform no matter what platform the program
is running on. This is known as pluggable look and feel.
Does
networking is support in Java ?
Yes, Java supports two types of
classes:
- Low-Level Classes: provide support for socket
programming like Socket, DatagramSocket, and ServerSocket classes.
- High-Level Classes: provide web programming URL,
URLEncoder, and URLConnection classes.
- Networking programming classes ease
the programming of network applications. Java networking like anything else in
Java is platform-independent.
Describe
java's security model.
The Java security model was
introduced in Java 2. It is divided into two pieces:
- User Adjustable Security Manager: checks various API operations like file access
- Byte Code Verifier:
that asserts the validity of compiled byte code.
- Public abstract class
SecurityManager java.lang. SecurityManager is an abstract class which helps to
different applications subclass to implement a particular security policy. It
allows an application to determine whether or not a particular operation will
generate a security exception.
What
is Race condition?
- Race Condition: It is the situation when two threads raise the request for
the same resource allocation, but the manner in which resources are allocated
are significant, is called race conditions.
- Race condition is created in program in order to run
the parallel execution of program by using multiple threads in a same
period.
- A race condition occurs when two threads operate on
same object without proper synchronization and there operation interleaves
on each other.
- The risk of Race condition is higher in Java.
What
is difference between StringBuffer and StringBuilder in Java?
The difference between StringBuffer
and StringBuilder are following:
- StringBuffer is uses mutable String, all public methods
are synchronized which makes it thread-safe but same time slow but In JDK
5 they provided StringBuilder which is copy of StringBuffer without
synchronization.
- StringBuilder is compatible with StringBuffer, but
synchronization property is may not compatible.
- StringBuilder is a little faster than StringBuffer.
What
is Marker Interface?
- Marker interface in Java is
interfaces with no field or methods. Uses of Mark Interfaces are following:
- We use Marker interface to tell java complier to add
special behavior to the class implementing it.
- Java marker interface has no members in it.
- It is implemented by classes in get some functionality.
Example: when we want to save the
state of an object then we implement serializable interface.
What
is the main difference between shallow cloning and deep cloning of objects?
The differences between shallow
cloning and deep cloning are:
- Java supports shallow cloning of objects by default
when a class implements the java.lang.Cloneable interface where as Deep
cloning is faster to develop and easier to maintain but carries a
performance overhead.
- A shallow is a copy of the collection structure whereas
Deep cloning copies duplicate everything.
- In Shallow copy, individual elements can be shared
between two collection but in case of deep cloning two collections with
all of the elements is the original collection duplicate.
What
are the difference between throw and throws?
The differences are between throw
and throws are:
- Throw is used to trigger an exception where as throws
is used in declaration of exception.
- Without throws, Checked exception cannot be handled
where as checked exception can be propagated with throws.
- Throw is used inside the method where as throws is used
with the method signature.
- Throw is followed by an instance but throws is followed
by class.
What
is difference between preemptive scheduling and time slicing?
Differences between preemptive and
time scheduling are:
- In Preemptive scheduling the highest priority task
executes until it enters the waiting or dead stated or a higher priority
task comes into existence.
- Time slicing, a task executes for a predefined time
period and then the pool of ready tasks. The scheduler then determines
which task should execute next, based on priority and other factor.
What
differences are between submit and execute method with ThreadPoolExecutor?
The difference between submit and
execute method with ThreadPoolExecutor are:
- When our tasks throw an exception and if it was
submitted with execute this exception will go to the uncaught exception
handler. If you submitted the task with submit any thrown exception,
checked or not, is then part of the task return status.
What
is the difference between final, finally and finalize methods in Java?
Final – a key word to define constants.
- After declaring a class as final we cannot divide it
into subclasses.
- When a method is marked final, it cannot be overridden by
the subclass.
- When a field is marked final, its value once set,
cannot be reset.
Finally – The finally block is always used with try and catch
blocks, except that, when try block uses System.exit(0) call.
- It is ensured for unexpected error, the finally block
do the execution which is mention in last clause of a try catch block.
- It is a block of statements that is executed
irrespective if or if not an exception was caught in the preceding try
block.
Finalize() – This method is linked
with garbage collection.
- This method is invoked automatically, just before the
collection of garbage value.
What
are the types of casting?
There are two types of casting:
- Casting between primitive numeric types, and
- Casting between object references.
Casting between numeric types is
used to convert larger values, like double values, to smaller values, such as
byte values. Casting between object references is used to refer to an object by
a compatible class, interface, or array type reference.
Describe
what happens when an object is created in Java.
Several things happen in a
particular order to ensure the object is constructed properly:
1. Memory allocation: To hold all instance variables and implementation-specific
data of the object and its super classes.
2. Initialization: the objects are initialized to their default values.
3. Constructor: Constructors call the constructors for its super
classes. This process continues until the constructor for java.lang.Object is
called, as java.lang.Object is the base class for all objects in java.
4. Execution: Before the body of the constructor is executed all
instance variable initializes and initialization blocks must get executed. Then
the body of the constructor is executed.
Core java interview questions
for experienced
• Yes,an inner class may be built an
Interface
Example :
public interface xyz
{
static int p=0;
void m();
class c
{
c()
{
int q;
System.out.println("inside");
};
public static void main(String c[])
{
System.out.println("inside ");
}
}
}
Why
is explicit object casting needed?
In order to assign a superclass
object in a variable to a subclass,one needs to do explicit casting.
For example:
Person person;
Man man;
man = (Man)person;
An automatic casting takes place when we typecast a object in subclass as
parent class object.
Define
Externalizable.
• Externalizable is coined as an
Interface
• It extends the Serializable Interface.
• It also sends data into the Streams.
• Externalizable sends data in a Compressed Format.
• Externalizable is having two methods,for e.g. writeExternal(ObjectOuput out)
& readExternal(ObjectInput in)
How
can a collection object be sorted?
• // Sort
Collections.sort(list);
• // Sort case-insensitive
Collections.sort(list, String.CASE_INSENSITIVE_ORDER);
• // SortReverse-order
Collections.sort(list, Collections.reverseOrder ());
• // Reverse-order sort case-insensitive
Collections.sort(list, String.CASE_INSENSITIVE_ORDER);
Collections.reverse(list);
Define
local, member and a class variable.
• Within a method variables declared
are called “local” variables.
• Variables declared in the class i.e not in any methods are “member” variables
(global variables).
• Variables declared in the class i.e not in any methods and are called as
“static” are class variables
Name
the different identifier states of a Thread.
Different types of identifiers of a
Thread are:
• R - Running or runnable thread
• S - Suspended thread
• CW - Thread waiting on a condition variable
• MW - Thread waiting on a monitor lock
• MS - Thread suspended waiting on a monitor lock
Define
Vector class? Differentiate the Vector and ArrayList.
• Vector canbe said a legacy class
which has been introduced to implement the List interface since Java 2 platform
v1.2
• Vector is always synchronized but ArrayList is not.
• When Vector class is synchronized, if we will run in multithreading
environment we've to use ArrayList with Collections.
• Vector has a default size i.e 10 while arrayList has no default size .
• ArraayList is not having any method returning Enumerations where as vector
list is having.
Differentiate
between Enumeration and Iterator interface
• In java.util package the
Enumeration and Iterator are available.
• The Enumeration interface is replicated by the Iterator interface.
• In preference to Enumeration new implementations should consider using
Iterator .
The difference of Iterators from enumerations are:
• Enumeration has 2 methods namely hasMoreElements() & nextElement() where
the Iterator contained three methods namely hasNext(), next(),remove().
• An optional remove operation is added in Iterator,and has shorter method
names. We Use remove() to delete the objects but the Enumeration interface does
not support this feature.
• The legacy classes use Enumeration interface .Vector.elements() &
Hashtable.elements() method results Enumeration. All Java Collections Framework
classes returns iterator.java.util.Collection.iterator() method returning an
instance of Iterator.
What
are the alternatives to inheritance?
• Delegation is an alternative to
inheritance.
• Delegation denotes that you include an instance of any class as an instance
variable, and forward messages to the instance.
• It is safer than inheritance because it ceases you to think about forwarded
message , because the instance is of a known class, rather than a new class,
and because it doesn’t force you to accept all the methods of the super class:
you can provide only the methods that really make sense.
• On the other hand, it makes you write more code, and it is harder to re-use
(because it is not a subclass).
Number
the bits, used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
• Unicode requires 16 bits
• ASCII require 7 bits. but it is usually represented as 8 bits.
• UTF-8 represents characters using 8, 16, and 18 bit patterns.
• UTF-16 uses 16-bit and larger bit patterns.
Define
reflection
• Reflection allows program related
access to information about the fields, methods and constructors of loaded
classes
• It use reflected fields, methods, and constructors
• It helps to operate on their underlying counterparts on objects,
• It operates within security restrictions.
What
is RMI and how it is useful?
• Remote method invocation is called
RMI.
• One can work with remote object using RMI .
• It gives a impression that you are working with a object that resides within
your own JVM though it is somewhere.
• The protocol used by RMI is RMI-IIOP
Define
a Collection API.
• The set of classes and interfaces
supporting the operation on collections of objects is the Collection API .
• Than the vectors, arrays, and hashtables if effectively replaces,these
classes and interfaces are more flexible, more powerful, and more regular
• class examples: HashSet, TreeMap, ArrayList, LinkedList,HashMap and TreeMap.
• interface examples: Set,List ,Collection and Map.
How
many forms of Polymorphism are there?
polymorphism exists in three
different forms in Java:
• Method overloading
• Method overriding through inheritance
• Method overriding through the Java interface
Define
the wrapper classes in Java and name a few.
• Wrapper class is wraps around the
primitive data type.
• list of the primitive types and the corresponding wrapper classes:
Primitive Wrapper
boolean java.lang.Boolean
byte java.lang.Byte
char java.lang.Character
double java.lang.Double
float java.lang.Float
int java.lang.Integer
long java.lang.Long
short java.lang.Short
void java.lang.Void
Differentiate
between JDK ,JRE & JVM
• JDK stands for Java Development
Kit.
It is the most widely used Java Software Development Kit.
• JRE stands for Java Runtime Environment
It is an implementation of the Java Virtual Machine which executes Java
programs
• JVM stands for Java Virtual Machine. It is an interpreter.
Why
will you use Comparator and Comparable interfaces?
• java.util.Comparator
• java.util.Comparator compares some other class’s instances,
• java.lang.Comparable
• java.lang.Comparable compares another object with itself .
Differentiate
between final, finally and finalize.
• The keyword is final.
It is used for declaring a constant
It prevents a class from producing subclasses.
• finally is a code.
It always executes when the try block is finished,
Unless System.exit() has been called.
• finalize() is a method,
Before discarding by the garbage collector it is invoked .
Differentiate
JAR and WAR file
JAR files:
• JAR files is the acronym stands for Java ARchive fles.
• JAR files allow aggregating many files into one,
• JAR is usually used to hold Java classes in a library.
WAR files:
• WAR files is the acronym stands for Web ARchive fles.
• WAR stores XML, java classes, and JavaServer pages
• WAR is mainly used for Web Application purposes.`
In
a Java , how can you send program messages on the system console, but error
messages, to a file?
• The class System has a variable
out that denotes the standard output,
• the standard error device represents the variable err .
• Naturally, they both point at the system console.
In this way, the standard output can be sent to the file:
Stream x = new Stream(new FileOutputStream("error.txt"));
System.setErr(x);
System.Out(x);
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