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.
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 m1 method, 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.
JAVA INTERVIEW QUESTION:
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.
