1. What
is selenium IDE
2. What
is Selenium RC
3. What
is Webdriver
4. What
is Selenium Grid
5. What
is difference between all of them
6. How
many browsers are supprted by IDE?
7. Can
we do Iphone and Android testing with Selenium
8. How
many browsers are supported by RC?
9. How
many Browsers are supported by WebDriver?
10. Difference
between QTP and selenium
11. How
to test ajax applications with selenium
12. How
to use regular expressions in selenium script
13. How
do you parameterize the tests in Selenium IDE
14. How
do you parameterize the tests in Selenium RC/Webdriver
15. How
do you decide when to choose Datadrivern or Keyword driven frame work?
16. What
is locator? When do you use CSS selectors and xpaths?
17. What
is the use of listeners in selenium? What is soft listener?
18. Difference
between HASH table and list?
19. What_are_the_capabilities_of_Selenium_IDE
20. What
are Drawbacks of IDE
21. How
do you select the 2nd item in a List box or drop down.
22. What
is the first thing you need to do when working with RC
23. How
many ways can you start the selenium Server
24. How
do you identify an object using selenium?
25. How
will you find the time taken by page to load using selenium?
26. How
will you find if page has entirely loaded using selenium?
27. Brief
about your framework
28. What
is assertion and verification?
29. When
do you use assertions and when do you use verifications
30. How
do you generate reports using Selenium
31. Suppose
I have a object on 3 pages of my application.
32. How
will I find of the same object is on all the 3 pages
33. What
are complete and partial xpaths
34. How
do you deal with complete and partial xpaths in selenium
35. How
do you deal with user extensions?
---------------------------
Selenium
Sampleinterview Questions
In
your experience, what are some of the challenges with Selenium?
Some
Challenges:
The
use of the locators need to be carefully thought through.
Handling
Dynamic Elements
Handling
Ajax Call Element
Handling
Http's URL's
2.What
is the difference between an assert and a verify with Selenium commands?
Assert:
Will fail and abort the current test execution.
Verify:
Will fail and continue to run the test execution.
3.How
many testing frameworks can QA Tester use in Selenium RC?
Testing
frameworks aren’t required, but they can be helpful if QA Tester wants to
automate test cases. Selenium RC supports Bromine, JUnit, NUnit, RSpec (Ruby),
Test::Unit (Ruby), TestNG (Java), unittest (Python).
4.Does
Selenium support mobile internet testing?
Selenium
supports Opera and opera is used in most of the Smart phones. So whichever
Smart phone supports opera, selenium can be used to test. So, one can use
Selenium RC to run the tests on mobiles
5.
What are the basic annotations used to run TestNG tests in Selenium?
The
basic annotations used to run TestNG tests in Selenium RC:
1.
@BeforeClass: The annotated method with @BeforeClass will be run before the
first test method in the current class is invoked.
2.
@AfterClass: The annotated method with @AfterClass will be run after all the
test methods in the current class have been run.
3.
@BeforeMethod: The annotated method with @BeforeMethod will be run before each
test method.
4.
@AfterMethod: The annotated method with @AfterMethod will be run after each
test method.
5.
@Test: Marks a class or a method @Test with as part of the test.
6.What
is the difference between Thread.Sleep() and Selenium.setSpeed()
Selenium.setSpeed:
1.
takes a single argument in string format
ex:
selenium.setSpeed(“2000″) – will wait for 2 seconds
2.
Runs each command in after setSpeed delay by the number of milliseconds
mentioned in setSpeed.
Thread.sleep:
1.
takes a single argument in integer format
ex:
thread.sleep(2000) – will wait for 2 seconds
2.
Waits for only once at the command given at sleep.
7.
How to configure Selenium RC with eclipse to run Junit Tests?
Download
eclipse. click here to download the software
2)
Open eclipse -> Workspace Launcher window will open
3)
Create a workspace by giving meaningful name
3)
Click on Workbench
4)
Create a project of type java
5)
Create a package under src folder of the package
6)
Add Junit to the build path
7)
Add selenium rc java client driver to the build path
8)
Now drag and drop your test script (.which is exported from Selenium IDE) to
the package created.
8.Which
browsers does WebDriver support?
The
existing drivers are the ChromeDriver, InternetExplorerDriver, FirefoxDriver,
OperaDriver and HtmlUnitDriver. For more information about each of these,
including their relative strengths and weaknesses, please follow the links to
the relevant pages. There is also support for mobile testing via the
AndroidDriver and IPhoneDriver.
9.What
is Web Driver?
Web
Driver uses a different underlying framework from Selenium’s javascript
Selenium-Core. It also provides an alternative API with functionality not supported
in Selenium-RC. WebDriver does not depend on a JavaScript core embedded within
the browser; therefore it is able to avoid some long-running Selenium
limitations.
WebDriver’s
goal is to provide an API that establishes
A
well-designed standard programming interface for web-app testing.
•
Improved consistency between browsers.
10.
Describe Technical Problems that you had with selenium tool
11.Wht
does SIDE Stands for
ans:Selenium
IDE
12.What
Programming Languages is best for writing the Selenium Tests
13.Compare
QTP vs Selenium
14.Can
tests recorded using Selenium IDE be run in other browsers?
Ans:Yes.
Although Selenium IDE is a Firefox add on, however, tests created in it can
also be run in other browsers by using Selenium RC (Selenium Remote Control)
and specifying the name of the test suite in command line.
15.What
are the locators available in Selenium?
16..What
is the difference between single and double slash in Xpath
Ans : / selects children of the context node,
// selects descendants of the context node.
17.
what is the diffarence b/w TestNG and Junit
18.
Explain about your reporting method
19.
How do you handle the secured connection error in HTTPS?
20.
How do you handle Ajax controls using selenium?
21.
Diffarent Types of Automation Framework
22.what
is the diffarence between Implicit and Explicit wait in selenium
23.
How to Handle the webTable data using Selenium
24.What
is the diffarence between actions, accessors,assertions
1.What
are the principle concepts of OOPS?
There
are four principle concepts upon which object oriented design and programming
rest. They are:
Abstraction
Polymorphism
Inheritance
Encapsulation
(i.e. easily remembered as A-PIE).
2.What is Abstraction?
Abstraction
refers to the act of representing essential features without including the
background details or explanations.
3.What is 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.
4.What is the difference between abstraction and encapsulation?
Abstraction
Abstraction
Encapsulation
is
the deliverables of Abstraction. Encapsulation barely talks about grouping up
your abstraction to suit the developer needs. solves the problem in the design
side while Encapsulation is the Implementation.
5.What is Inheritance?
Inheritance
is the process by which objects of one class acquire the properties of objects
of another class.
A
class that is inherited is called a superclass.
The
class that does the inheriting is called a subclass.
Inheritance
is done by using the keyword extends.
The
two most common reasons to use inheritance are:
To
promote code reuse
To
use polymorphism
6.What is Polymorphism?
Polymorphism
is briefly described as "one interface, many implementations."
Polymorphism is a characteristic of being able to assign a different meaning or
usage to something in different contexts - specifically, to allow an entity
such as a variable, a function, or an object to have more than one form.
7.How does Java implement polymorphism?
(Inheritance,
Overloading and Overriding are used to achieve Polymorphism in java).
Polymorphism manifests itself in Java in the form of multiple methods having the same name.
Polymorphism manifests itself in Java in the form of multiple methods having the same name.
In
some cases, multiple methods have the same name, but different formal argument
lists (overloaded methods).
In
other cases, multiple methods have the same name, same return type, and same
formal argument list (overridden methods).
8.Explain the different forms of Polymorphism.
There
are two types of polymorphism one is Compile time polymorphism and
the other is run time polymorphism. Compile time polymorphism is method
overloading. Runtime time polymorphism is done using inheritance and
interface.
Note: From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in Java:
Note: From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in Java:
Method
overloading
Method
overriding through inheritance
Method
overriding through the Java interface
9.What is runtime polymorphism or dynamic method dispatch?
In
Java, 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 superclass. The determination of the method to be
called is based on the object being referred to by the reference variable.
10.What is Dynamic Binding?
Binding
refers to the linking of a procedure call to the code to be executed in
response to the call. Dynamic binding (also known as late binding) means that
the code associated with a given procedure call is not known until the time of
the call at run-time. It is associated with polymorphism and inheritance.
11.What is method overloading?
Method
Overloading means to have two or more methods with same name in the same class
with different arguments. The benefit of method overloading is that it allows
you to implement methods that support the same semantic operation but differ by
argument number or type.
Note:
Note:
Overloaded
methods MUST change the argument list
Overloaded
methods CAN change the return type
Overloaded
methods CAN change the access modifier
Overloaded
methods CAN declare new or broader checked exceptions
A
method can be overloaded in the same class or in a subclass
12.What is method overriding?
Method
overriding occurs when sub class declares a method that has the same type
arguments as a method declared by one of its superclass. The key benefit of
overriding is the ability to define behavior that’s specific to a particular
subclass type.
Note:
Note:
The
overriding method cannot have a more restrictive access modifier than the
method being overridden (Ex: You can’t override a method marked public and make
it protected).
You
cannot override a method marked final
You
cannot override a method marked static
13.What are the differences between method overloading and method overriding?
|
|
Overloaded
Method
|
Overridden
Method
|
|
Arguments
|
Must
change
|
Must
not change
|
|
Return
type
|
Can
change
|
Can’t
change except for covariant returns
|
|
Exceptions
|
Can
change
|
Can
reduce or eliminate. Must not throw new or broader checked exceptions
|
|
Access
|
Can
change
|
Must
not make more restrictive (can be less restrictive)
|
|
Invocation
|
Reference
type determines which overloaded version is selected. Happens at compile
time.
|
Object
type determines which method is selected. Happens at runtime.
|
14.Can overloaded methods be override too?
Yes,
derived classes still can override the overloaded methods. Polymorphism can
still happen. Compiler will not binding the method calls since it is
overloaded, because it might be overridden now or in the future.
15.Is it possible to override the main method?
NO,
because main is a static method. A static method can't be overridden in Java.
16.How to invoke a superclass version of an Overridden method?
To
invoke a superclass method that has been overridden in a subclass, you must
either call the method directly through a superclass instance, or use the super
prefix in the subclass itself. From the point of the view of the subclass, the
super prefix provides an explicit reference to the superclass' implementation
of the method.
//
From subclass
super.overriddenMethod();
17.What is super?
super
You
can only go back one level.
In
the constructor, if you use super(), it must be the very first code, and you
cannot access any
is
a keyword which is used to access the method or member variables from the
superclass. If a method hides one of the member variables in its superclass,
the method can refer to the hidden variable through the use of the super
keyword. In the same way, if a method overrides one of the methods in its
superclass, the method can invoke the overridden method through the use of the
super keyword.
Note: this.xxx variables or methods to compute its parameters.
Note: this.xxx variables or methods to compute its parameters.
18.How do you prevent a method from being overridden?
To
prevent a specific method from being overridden in a subclass, use the final modifier
on the method declaration, which means "this is the final implementation
of this method", the end of its inheritance hierarchy.
public
final void exampleMethod() {
// Method statements
}
// Method statements
}
19.What is an Interface?
An
interface is a description of a set of methods that conforming implementing
classes must have.
Note:
Note:
You
can’t mark an interface as final.
Interface
variables must be static.
An
Interface cannot extend anything but another interfaces.
20.
You
can’t instantiate an interface directly, but you can instantiate a class that
implements an interface.
21.Can we create an object for an interface?
Yes,
it is always necessary to create an object implementation for an interface.
Interfaces cannot be instantiated in their own right, so you must write a class
that implements the interface and fulfill all the methods defined in it.
22.Do interfaces have member variables?
Interfaces
may have member variables, but these are implicitly
public,
static, and final- in other words, interfaces can declare only
constants, not instance variables that are available to all implementations and
may be used as key references for method arguments for example.
23.What modifiers are allowed for methods in an Interface?
Only
public and abstract modifiers
are allowed for methods in interfaces.
24.What is a marker interface?
Marker
interfaces are those which do not declare any required methods, but signify
their compatibility with certain operations. The
java.io.Serializable interface
and Cloneable are typical marker interfaces. These do not contain any
methods, but classes must implement this interface in order to be serialized
and de-serialized.
25.What is an abstract class?
Abstract
classes are classes that contain one or more abstract methods. An abstract
method is a method that is declared, but contains no implementation.
Note:
Note:
If
even a single method is abstract, the whole class must be declared abstract.
Abstract
classes may not be instantiated, and require subclasses to provide
implementations for the abstract methods.
You
can’t mark a class as both abstract and final.
26.Can we instantiate an abstract class?
An
abstract class can never be instantiated. Its sole purpose is to be extended
(subclassed).
27.What are the differences between Interface and Abstract class?
|
Abstract
Class
|
Interfaces
|
|
An
abstract class can provide complete, default code and/or just the details
that have to be overridden.
|
An
interface cannot provide any code at all,just the signature.
|
|
In
case of abstract class, a class may extend only one abstract class.
|
A
Class may implement several interfaces.
|
|
An
abstract class can have non-abstract methods.
|
All
methods of an Interface are abstract.
|
|
An
abstract class can have instance variables.
|
An
Interface cannot have instance variables.
|
|
An
abstract class can have any visibility: public, private, protected.
|
An
Interface visibility must be public (or) none.
|
|
If
we add a new method to an abstract class then we have the option of providing
default implementation and therefore all the existing code might work
properly.
|
If
we add a new method to an Interface then we have to track down all the
implementations of the interface and define implementation for the new
method.
|
|
An
abstract class can contain constructors .
|
An
Interface cannot contain constructors .
|
|
Abstract
classes are fast.
|
Interfaces
are slow as it requires extra indirection to find corresponding method in the
actual class.
|
28.When should I use abstract classes and when should I use interfaces?
Use
Interfaces when…
Use
Abstract Class when…
If
various implementations are of the same kind and use common behavior or status
then abstract class is better to use.
When
you want to provide a generalized form of abstraction and leave the
implementation task with the inheriting subclass.
Abstract
classes are an excellent way to create planned inheritance hierarchies. They're
also a good choice for nonleaf classes in class hierarchies.
29.When you declare a method as abstract, can other nonabstract methods access it?
Yes,
other nonabstract methods can access a method that you declare as abstract.
30.Can there be an abstract class with no abstract methods in it?
Yes,
there can be an abstract class without abstract methods.
31.
A
constructor is a special method whose task is to initialize the object of its
class.
It
is special because its name is the same as the class name.
They
do not have return types, not even void and therefore they cannot
return values.
They cannot
be inherited, though a derived class can call the base class constructor.
Constructor
is invoked whenever an object of its associated class is created.
32.How does the Java default constructor be provided?
If
a class defined by the code does not have any constructor, compiler
will automatically provide one no-parameter-constructor (default-constructor)
for the class in the byte code. The access modifier (public/private/etc.) of
the default constructor is the same as the class itself.
33.Can constructor be inherited?
No,
constructor cannot be inherited, though a derived class can call the base class
constructor.
34.What are the differences between Contructors and Methods?
|
|
Constructors
|
Methods
|
|
Purpose
|
Create
an instance of a class
|
Group
Java statements
|
|
Modifiers
|
Cannot
be abstract, final, native, static, orsynchronized
|
Can
be abstract, final, native, static, orsynchronized
|
|
Return
Type
|
No
return type, not even void
|
void
or a valid return type
|
|
Name
|
Same
name as the class (first letter is capitalized by convention) -- usually a
noun
|
Any
name except the class. Method names begin with a lowercase letter by
convention -- usually the name of an action
|
|
this
|
Refers
to another constructor in the same class. If used, it must be the first line
of the constructor
|
Refers
to an instance of the owning class. Cannot be used by static methods.
|
|
super
|
Calls
the constructor of the parent class. If used, must be the first line of the
constructor
|
Calls
an overridden method in the parent class
|
|
Inheritance
|
Constructors
are not inherited
|
Methods
are inherited
|
35.How are this() and super() used with constructors?
Constructors
use this to refer to another constructor in the same class with a
different parameter list.
Constructors
use super to invoke the superclass's constructor. If a constructor
uses super, it must use it in the first line; otherwise, the compiler will
complain.
36.What are the differences between Class Methods and Instance Methods?
|
Class
Methods
|
Instance
Methods
|
|
Class
methods are methods which are declared as static. The method can be called
without creating an instance of the class
|
Instance
methods on the other hand require an instance of the class to exist before
they can be called, so an instance of a class needs to be created by using
the new keyword.
Instance methods operate on specific instances of classes. |
|
Class
methods can only operate on class members and not on instance members as
class methods are unaware of instance members.
|
Instance
methods of the class can also not be called from within a class method unless
they are being called on an instance of that class.
|
|
Class
methods are methods which are declared as static. The method can be called
without creating an instance of the class.
|
Instance
methods are not declared as static.
|
37.How are this() and super() used with constructors?
Constructors
use this to refer to another constructor in the same class with a
different parameter list.
Constructors
use super to invoke the superclass's constructor. If a constructor
uses super, it must use it in the first line; otherwise, the compiler will
complain.
38.What are Access Specifiers?
One
of the techniques in object-oriented programming is encapsulation. It
concerns the hiding of data in a class and making this class available only
through methods. Java allows you to control access to classes, methods, and
fields via so-called access specifiers..
39.What are Access Specifiers available in Java?
Java
offers four access specifiers, listed below in decreasing accessibility:
Public
Protected
Default(no
specifier)-
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 visible within
subclasses and are not inherited by subclasses. If you 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, but not
from outside this package. - protected methods and fields can
only be accessed within the same class to which the methods and fields belong,
within its subclasses, and within classes of the same package. - public classes,
methods, and fields can be accessed from everywhere.
|
Situation
|
public
|
protected
|
default
|
private
|
|
Accessible
to class
from same package? |
yes
|
yes
|
yes
|
no
|
|
Accessible
to class
from different package? |
yes
|
no, unless
it is a subclass
|
no
|
no
|
40.What is final modifier?
The final modifier
keyword makes that the programmer cannot change the value anymore. The actual
meaning depends on whether it is applied to a class, a variable, or a method.
final
final
final
Methods-
A final method cannot be overridden by subclasses. Variables- A final
variable cannot be changed once it is initialized.Classes- A final class cannot
have subclasses.
There
are two reasons for marking a method as final:
Disallowing
subclasses to change the meaning of the method.
Increasing
efficiency by allowing the compiler to turn calls to the method into inline
Java code.
42.What is static block?
Static
block which exactly executed exactly once when the class is first loaded into
JVM. Before going to the main method the static block will execute.
43.What are static variables?
Variables
that have only one copy per class are known as static variables. They are not
attached to a particular instance of a class but rather belong to a class as a
whole. They are declared by using the static keyword as a modifier.
static
type varIdentifier;
where,
the name of the variable is varIdentifier and its data type is specified by
type.
Note: Static variables that are not explicitly initialized in the code are automatically initialized with a default value. The default value depends on the data type of the variables.
Note: Static variables that are not explicitly initialized in the code are automatically initialized with a default value. The default value depends on the data type of the variables.
44.What is the difference between static and non-static variables?
A
static variable is associated with the class as a whole rather than with
specific instances of a class. Non-static variables take on unique values with
each object instance.
45.
Methods
declared with the keyword static as modifier are called static methods or class
methods. They are so called because they affect a class as a whole, not a
particular instance of the class. Static methods are always invoked without
reference to a particular instance of a class.
Note:The use of a static method suffers from the following restrictions:
Note:The use of a static method suffers from the following restrictions:
A
static method can only call other static methods.
A
static method must only access static data.
A
static method cannot reference to the current object using keywords
super or this.
1.
What is the most important feature of Java?
Java
is a platform independent language.
2.
What do you mean by platform independence?
Platform
independence means that we can write and compile the java code in one platform
(eg Windows) and can execute the class in any other supported platform eg
(Linux,Solaris,etc).
3.
What is a JVM?
JVM
is Java Virtual Machine which is a run time environment for the compiled java
class files.
4.
Are JVM's platform independent?
JVM's
are not platform independent. JVM's are platform specific run time
implementation provided by the vendor.
5.
What is the difference between a JDK and a JVM?
JDK
is Java Development Kit which is for development purpose and it includes
execution environment also. But JVM is purely a run time environment and hence
you will not be able to compile your source files using a JVM.
6.
What is a pointer and does Java support pointers?
Pointer
is a reference handle to a memory location. Improper handling of pointers leads
to memory leaks and reliability issues hence Java doesn't support the usage of
pointers.
7.
What is the base class of all classes?
java.lang.Object
8.
Does Java support multiple inheritance?
Java
doesn't support multiple inheritance.
9.
Is Java a pure object oriented language?
Java
uses primitive data types and hence is not a pure object oriented language.
10.
Are arrays primitive data types?
In
Java, Arrays are objects.
11.
What is difference between Path and Classpath?
Path
and Classpath are operating system level environment variales. Path is used
define where the system can find the executables(.exe) files and classpath is
used to specify the location .class files.
12.
What are local variables?
Local
varaiables are those which are declared within a block of code like methods.
Local variables should be initialised before accessing them.
13.
What are instance variables?
Instance
variables are those which are defined at the class level. Instance variables
need not be initialized before using them as they are automatically initialized
to their default values.
14.
How to define a constant variable in Java?
The
variable should be declared as
static and final.
So only one copy of the variable exists for all instances of the class and the
value can't be changed also.static final int PI = 2.14; is an example for
constant.
15.
Should a main() method be compulsorily declared in all java classes?
No
not required.
main() method
should be defined only if the source class is a java application.
16.
What is the return type of the main() method?
Main()
method
doesn't return anything hence declared void.
17.
Why is the main() method declared static?
main()
method
is called by the JVM even before the instantiation of the class hence it is
declared as static.
18.
What is the arguement of main() method?
main()
method
accepts an array of String object as arguement.
19.
Can a main() method be overloaded?
Yes.
You can have any number of
main() methods
with different method signature and implementation in the class.
20.
Can a main() method be declared final?
Yes.
Any inheriting class will not be able to have it's own default
main() method.
21.
Does the order of public and static declaration matter in main() method?
No.
It doesn't matter but
void should
always come before main().
22.
Can a source file contain more than one class declaration?
Yes
a single source file can contain any number of Class declarations but only one
of the class can be declared as
public.
23.
What is a package?
Package
is a collection of related classes and interfaces. package declaration should
be first statement in a java class.
24.
Which package is imported by default?
java.lang
package
is
imported by default even without a package declaration.
25.
Can a class declared as private be accessed outside it's package?
Not
possible.
26.
Can a class be declared as protected?
A
class can't be declared as
protected.
only methods can be declared as protected.
27.
What is the access scope of a protected method?
A
protected method
can be accessed by the classes within the same package or by the subclasses of
the class in any package.
28.
What is the purpose of declaring a variable as final?
A
final variable's
value can't be changed. final variables should be initialized before
using them.
29.
What is the impact of declaring a method as final?
A
method declared as
final can't
be overridden. A sub-class can't have the same method signature with a different
implementation.
30.
I don't want my class to be inherited by any other class. What should i do?
You
should declared your class as
final.
But you can't define your class as final, if it is an abstract class.
A class declared as final can't be extended by any other class.
31.
Can you give few examples of final classes defined in Java API?
java.lang.String,
java.lang.Math
are final classes.
32.
How is final different from finally and finalize()?
final
is
a modifier which can be applied to a class or a method or a variable. final class
can't be inherited, final method can't be overridden and final variable
can't be changed.
finally is an exception handling code section which gets executed whether an exception is raised or not by the try block code segment.
finalize() is a method of Object class which will be executed by the JVM just before garbage collecting object to give a final chance for resource releasing activity.
finally is an exception handling code section which gets executed whether an exception is raised or not by the try block code segment.
finalize() is a method of Object class which will be executed by the JVM just before garbage collecting object to give a final chance for resource releasing activity.
33.
Can a class be declared as static?
We
can not declare top level class as static, but only inner class can be declared
static.
public
class Test
{
static
class InnerClass
{
public
static void InnerMethod()
{
System.out.println("Static Inner Class!"); }
}
public
static void main(String args[])
{
Test.InnerClass.InnerMethod();
}
}
//output:
Static Inner Class!
34.
When will you define a method as static?
When
a method needs to be accessed even before the creation of the object of the
class then we should declare the method as
static.
35.
What are the restriction imposed on a static method or a static block of code?
A
static method should not refer to instance variables without creating an
instance and cannot use "this" operator to refer the instance.
36.
I want to print "Hello" even before main() is executed. How will you
acheive that?
Print
the statement inside a static block of code. Static blocks get executed when
the class gets loaded into the memory and even before the creation of an
object. Hence it will be executed before the
main() method.
And it will be executed only once.
37.
What is the importance of static variable?
static
variables are class level variables where all objects of the class refer to the
same variable. If one object changes the value then the change gets reflected
in all the objects.
38.
Can we declare a static variable inside a method?
Static
varaibles are class level variables and they can't be declared inside a method.
If declared, the class will not compile.
39.
What is an Abstract Class and what is it's purpose?
A
Class which doesn't provide complete implementation is defined as an abstract
class. Abstract classes enforce abstraction.
40.
Can a abstract class be declared final?
Not
possible. An abstract class without being inherited is of no use and hence will
result in compile time error.
41.
What is use of a abstract variable?
Variables
can't be declared as abstract. only classes and methods can be declared as
abstract.
42.
Can you create an object of an abstract class?
Not
possible. Abstract classes can't be instantiated.
43.
Can a abstract class be defined without any abstract methods?
Yes
it's possible. This is basically to avoid instance creation of the class.
44.
Class C implements Interface I containing method m1 and m2 declarations. Class
C has provided implementation for method m2. Can i create an object of Class C?
No
not possible.
Class
C should provide implementation for all the methods in the Interface
I. Since Class C didn't provide implementation for m1method, it
has to be declared as abstract. Abstract classes can't be instantiated.
45.
Can a method inside a Interface be declared as final?
No
not possible. Doing so will result in compilation error.
public and abstract are
the only applicable modifiers for method declaration in an interface.
46.
Can an Interface implement another Interface?
Intefaces
doesn't provide implementation hence a interface cannot implement another
interface.
47.
Can an Interface extend another Interface?
Yes
an Interface can inherit another Interface, for that matter an Interface can
extend more than one Interface.
48.
Can a Class extend more than one Class?
Not
possible. A Class can extend only one class but can implement any number of
Interfaces.
49.
Why is an Interface be able to extend more than one Interface but a Class can't
extend more than one Class?
Basically
Java doesn't allow multiple inheritance, so a Class is restricted to extend
only one Class. But an Interface is a pure abstraction model and doesn't have
inheritance hierarchy like classes(do remember that the base class of all
classes is Object). So an Interface is allowed to extend more than one
Interface.
50.
Can an Interface be final?
Not
possible. Doing so so will result in compilation error.
51.
Can a class be defined inside an Interface?
Yes
it's possible.
52.
Can an Interface be defined inside a class?
Yes
it's possible.
53.
What is a Marker Interface?
An
Interface which doesn't have any declaration inside but still enforces a
mechanism.
54.
Which object oriented Concept is achieved by using overloading and overriding?
Polymorphism.
55.
Why does Java not support operator overloading?
Operator
overloading makes the code very difficult to read and maintain. To maintain
code simplicity, Java doesn't support operator overloading.
56.
Can we define private and protected modifiers for variables in interfaces?
No.
57.
What is Externalizable?
Externalizable
is an Interface that extends Serializable Interface. And sends data into
Streams in Compressed Format. It has two methods,
writeExternal(ObjectOuput
out) and readExternal(ObjectInput in)
58.
What modifiers are allowed for methods in an Interface?
Only
public and abstract modifiers
are allowed for methods in interfaces.
59.
What is a local, member and a class variable?
Variables
declared within a method are "local" variables.
Variables
declared within the class i.e not within any methods are "member"
variables (global variables).
Variables
declared within the class i.e not within any methods and are defined as
"static" are class variables.
60.
What is an abstract method?
An
abstract method is a method whose implementation is deferred to a subclass.
61.
What value does read() return when it has reached the end of a file?
The
read() method
returns -1 when it has reached the end of a file.
62.
Can a Byte object be cast to a double value?
No,
an object cannot be cast to a primitive value.
63.
What is the difference between a static and a non-static inner class?
A
non-static inner class may have object instances that are associated with
instances of the class's outer class. A static inner class does not have any
object instances.
64.
What is an object's lock and which object's have locks?
An
object's lock is a mechanism that is used by multiple threads to obtain
synchronized access to the object. A thread may execute a synchronized method
of an object only after it has acquired the object's lock. All objects and
classes have locks. A class's lock is acquired on the class's Class object.
65.
What is the % operator?
It
is referred to as the modulo or remainder operator. It returns the remainder of
dividing the first operand by the second operand.
66.
When can an object reference be cast to an interface reference?
An
object reference be cast to an interface reference when the object implements
the referenced interface.
67.
Which class is extended by all other classes?
The
Object class is extended by all other classes.
68.
Which non-Unicode letter characters may be used as the first character of an
identifier?
The
non-Unicode letter characters
$ and _ may
appear as the first character of an identifier
69.
What restrictions are placed on method overloading?
Two
methods may not have the same name and argument list but different return
types.
70.
What is 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, such as 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.
71.
What is the return type of a program's main() method?
void.
72.
If a variable is declared as private, where may the variable be accessed?
A
private variable may only be accessed within the class in which it is declared.
73.
What do you understand by private, protected and public?
These
are accessibility modifiers.
Private is
the most restrictive, while public is the least restrictive. There is
no real difference between protected and the default type (also known
as package protected) within the context of the same package, however the
protected keyword allows visibility to a derived class in a different package.
74.
What is Downcasting ?
Downcasting
is the casting from a general to a more specific type, i.e. casting down the
hierarchy
75.
What modifiers may be used with an inner class that is a member of an outer
class?
A
(non-local) inner class may be declared as public, protected, private, static,
final, or abstract.
76.
How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8
characters?
Unicode
requires 16 bits and ASCII require 7 bits Although the ASCII character set uses
only 7 bits, 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.
77.
What restrictions are placed on the location of a package statement within a
source code file?
A
package statement must appear as the first line in a source code file
(excluding blank lines and comments).
78.
What is a native method?
A
native method is a method that is implemented in a language other than Java.
79.
What are order of precedence and associativity, and how are they used?
Order
of precedence determines the order in which operators are evaluated in
expressions. Associatity determines whether an expression is evaluated
left-to-right or right-to-left.
80.
Can an anonymous class be declared as implementing an interface and extending a
class?
An
anonymous class may implement an interface or extend a superclass, but may not
be declared to do both.
81.
What is the range of the char type?
The
range of the
char type
is 0 to 216 - 1 (i.e. 0 to 65535.)
82.
What is the range of the short type?
The
range of the
short type
is -(215) to 215 - 1. (i.e. -32,768 to 32,767)
83.
Why isn't there operator overloading?
Because
C++ has proven by example that operator overloading makes code almost
impossible to maintain.
84.
What does it mean that a method or field is "static"?
Static
variables and methods are instantiated only once per class. In other words they
are class variables, not instance variables. If you change the value of a
static variable in a particular object, the value of that variable changes for
all instances of that class. Static methods can be referenced with the name of
the class rather than the name of a particular object of the class (though that
works too). That's how library methods like
System.out.println() work.
out is a static field in the java.lang.System class.
85.
Is null a keyword?
The
null value is not a keyword.
86.
Which characters may be used as the second character of an identifier, but not
as the first character of an identifier?
The
digits 0 through 9 may not be used as the first character of an identifier but
they may be used after the first character of an identifier.
87.
Is the ternary operator written x : y ? z or x ? y : z ?
It
is written
x
? y : z.
88.
How is rounding performed under integer division?
The
fractional part of the result is truncated. This is known as rounding toward
zero.
89.
If a class is declared without any access modifiers, where may the class be
accessed?
A
class that is declared without any access modifiers is said to have package
access. This means that the class can only be accessed by other classes and
interfaces that are defined within the same package.
90.
Does a class inherit the constructors of its superclass?
A
class does not inherit constructors from any of its superclasses.
91.
Name the eight primitive Java types.
The
eight primitive types are byte, char, short, int, long, float, double, and
boolean.
92.
What restrictions are placed on the values of each case of a switch statement?
During
compilation, the values of each case of a
switch statement
must evaluate to a value that can be promoted to an int value.
93.
What is the difference between a while statement and a do while statement?
A
while statement
checks at the beginning of a loop to see whether the next loop iteration should
occur. A do while statement checks at the end of a loop to see
whether the next iteration of a loop should occur. The do whilestatement
will always execute the body of a loop at least once.
94.
What modifiers can be used with a local inner class?
A
local inner class may be
final or abstract.
95.
When does the compiler supply a default constructor for a class?
The
compiler supplies a default constructor for a class if no other constructors
are provided.
96.
If a method is declared as protected, where may the method be accessed?
A
protected method may only be accessed by classes or interfaces of the same
package or by subclasses of the class in which it is declared.
97.
What are the legal operands of the instanceof operator?
The
left operand is an object reference or null value and the right operand is a
class, interface, or array type.
98.
Are true and false keywords?
The
values true and false are not keywords.
99.
What happens when you add a double value to a String?
The
result is a String object.
100.
What is the diffrence between inner class and nested class?
When
a class is defined within a scope od another class, then it becomes inner
class. If the access modifier of the inner class is static, then it becomes
nested class.
101.
Can an abstract class be final?
An
abstract class may not be declared as
final.
102.
What is numeric promotion?
Numeric
promotion is the conversion of a smaller numeric type to a larger numeric type,
so that integer and floating-point operations may take place. In numerical
promotion, byte, char, and short values are converted to int values. The int
values are also converted to long values, if necessary. The long and float
values are converted to double values, as required.
103.
What is the 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.
104.
To what value is a variable of the boolean type automatically initialized?
The
default value of the boolean type is false.
105.
What is the difference between the prefix and postfix forms of the ++ operator?
The
prefix form performs the increment operation and returns the value of the
increment operation. The postfix form returns the current value all of the
expression and then performs the increment operation on that value.
106.
What restrictions are placed on method overriding?
Overridden
methods must have the same name, argument list, and return type. The overriding
method may not limit the access of the method it overrides. The overriding
method may not throw any exceptions that may not be thrown by the overridden
method.
107.
What is a Java package and how is it used?
A
Java package is a naming context for classes and interfaces. A package is used
to create a separate name space for groups of classes and interfaces. Packages
are also used to organize related classes and interfaces into a single API unit
and to control accessibility to these classes and interfaces.
108.
What modifiers may be used with a top-level class?
A
top-level class may be public, abstract, or final.
115.
What is constructor chaining and how is it achieved in Java ?
A
child object constructor always first needs to construct its parent (which in
turn calls its parent constructor.). In Java it is done via an implicit call to
the no-args constructor as the first statement.
116.
What is the difference between the Boolean & operator and the &&
operator?
If
an expression involving the Boolean & operator is evaluated, both operands
are evaluated. Then the & operator is applied to the operand. When an
expression involving the && operator is evaluated, the first operand is
evaluated. If the first operand returns a value of true then the second operand
is evaluated. The && operator is then applied to the first and second
operands. If the first operand evaluates to false, the evaluation of the second
operand is skipped.
117.
Which Java operator is right associative?
The
= operator is right associative.
118.
Can a double value be cast to a byte?
Yes,
a double value can be cast to a byte.
119.
What is the difference between a break statement and a continue statement?
A
break statement
results in the termination of the statement to which it applies (switch, for,
do, or while). A continuestatement is used to end the current loop
iteration and return control to the loop statement.
120.
Can a for statement loop indefinitely?
Yes,
a for statement can loop indefinitely. For example, consider the following:
for(;;);
Can
there be an abstract class with no abstract methods in it?
Can
an Interface be final?
Can
an Interface have an inner class?
-
Yes. - No
public
interface abc
{
static
int i=0; void dd();
class
a1
{
a1()
{
int
j;
System.out.println("inside");
};
public
static void main(String a1[])
{
System.out.println("in
interfia");
}
}
}
Can
we define private and protected modifiers for variables in interfaces?
What
is Externalizable?
What
modifiers are allowed for methods in an Interface?
What
is a local, member and a class variable?
What
are the different identifier states of a Thread?
What
are some alternatives to inheritance?
Why
isn’t there operator overloading?
What
does it mean that a method or field is "static"?
How
do I convert a numeric IP address like 192.18.97.39 into a hostname like
java.sun.com?
-
Static variables and methods are instantiated only once per class. In other
words they are class variables, not instance variables. If you change the value
of a static variable in a particular object, the value of that variable changes
for all instances of that class. Static methods can be referenced with the name
of the class rather than the name of a particular object of the class (though
that works too). That’s how library methods like System.out.println() work. out
is a static field in the java.lang.System class. - Because C++ has proven
by example that operator overloading makes code almost impossible to maintain.
In fact there very nearly wasn’t even method overloading in Java, but it was
thought that this was too useful for some very basic methods like print(). Note
that some of the classes like DataOutputStream have unoverloaded methods like
writeInt() and writeByte(). - Delegation is an alternative to inheritance.
Delegation means that you include an instance of another class as an instance
variable, and forward messages to the instance. It is often safer than
inheritance because it forces you to think about each message you forward,
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). -
The different 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 -
Variables declared within a method are "local" variables. Variables
declared within the class i.e not within any methods are "member"
variables (global variables). Variables declared within the class i.e not
within any methods and are defined as "static" are class variables -
Only public and abstract modifiers are allowed for methods in interfaces. -
Externalizable is an Interface that extends Serializable Interface. And sends
data into Streams in Compressed Format. It has two methods,
writeExternal(ObjectOuput out) and readExternal(ObjectInput in)
String
hostname = InetAddress.getByName("192.18.97.39").getHostName();
Difference
between JRE/JVM/JDK?
Why
do threads block on I/O?
What
is synchronization and why is it important?
Is
null a keyword?
Which
characters may be used as the second character of an identifier,but not as the
first character of an identifier?
What
modifiers may be used with an inner class that is a member of an outer class?
How
many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
What
are wrapped classes?
What
restrictions are placed on the location of a package statement within a source
code file?
What
is the difference between preemptive scheduling and time slicing?
What
is a native method?
What
are order of precedence and associativity, and how are they used?
What
is the catch or declare rule for method declarations?
Can
an anonymous class be declared as implementing an interface and extending a
class?
What
is the range of the char type?
-
The range of the char type is 0 to 2^16 - 1. - An anonymous class may
implement an interface or extend a superclass, but may not be declared to do
both. - If a checked exception may be thrown within the body of a method,
the method must either catch the exception or declare it in its throws clause. -
Order of precedence determines the order in which operators are evaluated in
expressions. Associatity determines whether an expression is evaluated
left-to-right or right-to-left - A native method is a method that is
implemented in a language other than Java. - 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. - A package statement must appear as the first
line in a source code file (excluding blank lines and comments). - Wrapped
classes are classes that allow primitive types to be accessed as objects. -
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character
set uses only 7 bits, 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. - A (non-local) inner class may be declared as public,
protected, private, static, final, or abstract. - The digits 0 through 9
may not be used as the first character of an identifier but they may be used
after the first character of an identifier. - The null value is not a
keyword. - With respect to multithreading, synchronization is the
capability to control the access of multiple threads to shared resources.
Without synchronization, it is possible for one thread to modify a shared
object while another thread is in the process of using or updating that
object’s value. This often leads to significant errors. - Threads block on
i/o (that is enters the waiting state) so that other threads may execute while
the I/O operation is performed.
-
No - Yes What are static methods?
1.What
are the uses of final method?
What
is Constructor?
You
see that something in your design will change frequently.
If
various implementations only share method signatures then it is better to use
Interfaces.
you
need some classes to use some methods which you don't want to be included in
the class, then you go for the interface, which makes it easy to just implement
and make use of the methods defined in the interface.
Can
we instantiate an interface?
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