Qus 1: What is Polymorphism?
Ans : The Polymorphism can be referred as one name many forms. It
is the ability of methods to behave differently, depending upon the object who
is calling it. The key features of Polymorphism are :
1. Allows using one interface for
multiple implementations.
2. Supports Method Overloading:
Multiple methods with same name, but different formal argument.
3. Supports Method Overridden:
Multiple methods have the same name, same return type, and same formal argument
list.
Qus 2: Explain garbage
collection.
Ans : The Java uses the garbage collection to free the memory. By
cleaning those objects that are no longer reference by any of the program. Step
involve in cleaning up the garbage collection :
Garbage Object Collection : First
step is to collection and group all those object which are no more reference
with any of the program. We can use the different methods to collect the
garbage object like using runtime.gc() or system.gc().
Run Finalize method : To free up
those object which is collected by the garbage collector java must execute the
Finalize method to delete all those dynamically created object.
Qus 3: What is an immutable object?
Ans : An immutable object is one that we cannot change once it is
created. Steps involved in creation of an immutable object are :
- Make all of its data fields
private.
- Methods which can perform
changes in any of the data fields after the construction of object must be
avoided.
Qus 4: How are this() and
super() used with constructors?
Ans : this() Constructors :
- It is used to pointing the
current class instance.
- It can be used with variables
or methods.
- It is used to call constructer
of same class.
- Private variable cannot be
accessed using this().
super() Constructer :
- It is used to call constructor
of parent class.
- Must be the first statement in
the body of constructor.
- Using this we can access
private variables in the super class.
Qus 5: What are Access Specifiers
available in Java?
Public : Public classes, methods,
and fields can be accessed by every class.
Protected : Protected methods and
fields can only be accessed within the same class to which the methods and
fields belong.
Default (no specifier) : When we
do not set access to specific level, then such a class, method, or field will
be accessible from inside the same package to which the class, method, or field
belongs.
Private : Private methods and
fields can only be accessed within the same class to which the methods and fields
belong. Private methods and fields are not inherited by subclasses.
Qus 6: What is Constructor?
- A constructor is used to
initialize a newly created object.
- It is called just after the
memory is allocated for the object.
- It can be used to initialize
the objects.
- It is not mandatory to write a
constructor for the class.
- Name of constructor is same as
the class name.
- They cannot be inherited.
- A constructor is invoked
whenever an object of its associated class is created.
Qus 7: What are the List interface and
its main implementation?
ArrayList : Resizable-array
implementation of the List interface.
Vector : Synchronized
resizable-array implementation of the List.
LinkedList : Doubly-linked list
implementation of the List interface. Better performance than the
ArrayList
implementation when elements are inserted or deleted timely.
Qus 8: Explain the user defined
Exceptions.
Ans : User Defined Exceptions are
exceptions defined by the user for specific purposed. This allows custom
exceptions to be generated and caught in the same way as normal exceptions.
While defining a User Defined Exception, we need to take care of the following
aspects :
- It should be extend from
Exception class.
- Use toString() method to
display information about the exception.
Qus 9: Describe life cycle of thread.
Ans : Threads follow the single flow of
control. A thread is execution in a program. The life cycles of threads are
listed below :
Newborn state : After the
creations of Thread instance the thread is in this state but before the start()
method invocation. Thread is considered not alive in this phase.
Runnable state : A thread starts
its life from Runnable state. After the invoking of start() method thread
enters Runnable state.
Running state : A thread first
enters Runnable state.
Blocked state : A thread can enter
in this state because of waiting the resources that are hold by another thread.
Dead state : A thread can be
considered dead when its run() method completes. If any thread comes on this
state that means it cannot ever run again.
Qus 10 :What is an Applets?
- These are small java programs.
- They can send from one computer
to another computer over the internet using the Applet Viewer that supports
java.
- Applets can run in a Web
browser as it is a java program. It can be a fully functional Java application
because it has the entire Java API at its disposal.
- Applets follow the security
rules given by the Web browser.
Qus 11 :What is the Set interface?
- A set interface is a collection
of element which cannot be duplicated.
- The set interface contains
methods inherited from the collection.
- It provides methods to access
the elements of a finite mathematical set.
- Two Set objects are equal if
they contain the same elements.
- It models the mathematical set
abstraction.
Qus 12 :What is a HashSet and TreeSet?
HashSet :
- The HashSet is an unsorted,
unordered Set.
- It is Collection set that
restricts duplicate elements and also repositioning of elements.
- It implements the Set interface
and extends AbstractSet.
- It uses hash code of the object
being inserted.
TreeSet :
- The TreeSet is a Set
implemented when we want elements in a sorted order.
- Sorting of element is done
according to the natural order of elements or by the help of comparator
provided at creation time.
How do you decide when to use
HashMap and when to use TreeMap and what is difference between these two?
- HashMap is used when we want to
perform insertion, deletion, and locate elements in a Map.
- TreeMap is used when we want to
traverse the elements in a sorted order. Depending upon the size of collection,
adding elements to HashMap is easy. For sorted elements traversal we can
convert the HashMap into TreeMap.
HashMap :
- Lets us to have null values and
also one null key
- Iterator in the HashMap is
Fail-Safe.
- It is Unsynchronized.
HashTable :
- It does not allow null value as
key and value.
- It is not synchronized.
Qus 13 :What is the Comparable interface?
- The Comparable interface is
used to sort collections and arrays of objects using the collections.sort() and
java.utils.
- The objects of the class
implementing the comparable interface can be ordered.
- All classes implementing the
Comparable interface must implement the compareTo() method that has the return
type as an integer.
- The signature of the
compareTo() method is as follows :
int i =
object1.compareTo(object2)
If object1 < object2: The
value of i returned will be negative.
If object1 > object2: The
value of i returned will be positive.
If object1 = object2: The value
of i returned will be zero.
Qus 14: When should I use abstract
classes and when should I use interfaces?
Use Interface, when :
- Design changing frequently or
when various implementations only share method signatures.
- We need some classes to use
some methods which we do not want to be included in the class.
Use Abstract Class, when :
- Various implementations are of
the same kind and use common behavior.
- Enabling with generalized form
of abstraction and leave the implementation task with the inheriting subclass.
- Creating planned inheritance
hierarchies.
Qus 15: Explain the Polymorphism
principle.
- The Polymorphism can be
referred as one name many forms. It is the ability of the methods to behave
differently, depending upon the object who is calling it.
- Polymorphism exists in three
distinct forms in java :
1. Method overloading
2. Method overriding through
inheritance
3. Method overriding through the
java interface
Qus 16: What are the difference between
throw and throws?
The difference between throw and
throws are :
- Throw is used to trigger an
exception where as throws is used in the 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.
Qus 17: 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.
Qus 18: Explain traversing through a
collector using Iterator.
We can access each element in the
collection by using Iterators irrespective of how they are organized in the
collector. Iterator can be implemented a different way for every Collection. To
use an iterator to traverse through the contents of a collection we do :
- Obtain an iterator by calling
the collections iterator()method to the start of the collection.
- Set up a loop that makes a call
to hasNext(). Have the loop iterate as long as hasNext()returns true.
- Within the loop, obtain each
element by calling next().
- The remove() method is used to
remove the current element in the iteration.
Qus 19: What are the principle concepts
of OOPS?
There are four principle concepts
upon which object oriented design and programming test. They are:
1. Abstraction : Abstraction refers to the act of
representing essential features without including the background details or
explanations.
2. Polymorphism : It is the ability to create a
variable, a function, or an object that has more than one form.
3. Inheritance : Inheritance is the process by
which objects of one class acquire the properties of objects of another class.
4. Encapsulation : Encapsulation is a technique used
for hiding the properties and behaviors of an object and allowing outside
access only as appropriate. It prevents other objects from directly altering or
accessing the properties or methods of the encapsulated object.
Qus 20: What are the basic features of
java?
The basic features of java are
given below :
- Java provides immense security.
- Java provides high portability.
- Java provides object oriented
programming features.
- Java provides robustness.
- Java is multithreaded.
- Java provides architecture
neutrality.
- Java is distributed.
- Java is dynamic.
Qus 21: How java becomes object oriented?
- Java follows the paradigm of Object Oriented programming.
- Java follows modular approach.
- Java follows the abstraction
aspect.
- Java follows the OO principle
encapsulation.
- Java follows the OO principle
polymorphism.
- Java follows the OO principle
inheritance.
Qus 22: How java becomes robust?
- Java provides multi-platform
environment.
- Java provides high reliability
in the design.
- Java is a strictly typed
language.
- Java checks the code at
runtime.
- Java provides predictability.
- java provides various keywords.
Qus 23: How a Java program compiles?
- First the source file name must
be extended with .java extension. e.g. Myprog.java
- Execute the javac compiler.
- javac compiler creates a file
called Myprog.class i.e. the bytecode version of Myprog.java.
- The bytecode is executed by the
Java runtime-systems which is called Java Virtual Machine (JVM).
- JVM is platform dependent.
Qus 24: What is 'public static void main
( String args[ ] ) ' signifies?
- The access specifier is the
'public' keyword .
- 'static' keyword allows main()
to be called without instantiating a particular instance of a class.
- 'void' affirms the compiler
that no value is returned by main().
- 'main()' method is called at
the beginning of a Java program.
- 'String args()' tells a
parameter named args,which is an instance array of class String.
Qus 25: What 'System.out.println()'
signifies?
- 'System' is a predefined class
.
- System class gives access to
the system.
- 'out' is the output stream.
- 'println' is printing the line
on the console.
- This is a console output
statement.
Qus 26: What is a variable in Java
program?
- It's a memory location.
- The memory location is given
some name.
- The memory location is being
assigned some value.
- The value may change of the
variable.
- The memory location size
changes with the type of the variable.
Qus 27: What is JVM?
- JVM is the acronym stands for
'Java Virtual Machine'.
- JVM provides the execution
environment.
- JVM is not platform
independent..
- JVM is the Java run-time system.
- JVM is an interpreter of
bytecode.
- JVM also makes the system
secured.
Qus 28 : What is bytecode?
- Bytecode is an instruction set.
- Bytecode extends with .class.
- 'javac' compiler translates the
.java file into .class.
- JVM interprets bytecode.
- Bytecode facility makes Java
platform-independent.
- It also confirms security to
the Java code.
Qus 29 : What is Java applet?
- Applet is a java program.
- It has been designed for
transmitting the Java code over the internet.
- It is automatically executed by
Java-enabled Web Browser.
- Applet can respond to the user
input.
- Applet is dynamically
programmed.
All the Best :-)