What is abstraction?
Abstraction is a process of hiding the implementation
details and showing only functionality to the user.
What is the difference between abstraction
and encapsulation?
Abstraction hides the implementation details whereas
encapsulation wraps code and data into a single unit
What is abstract
class?
A class that is declared as abstract is known as abstract
class. It needs to be extended and its method implemented. It cannot be
instantiated.
Can there be any
abstract method without abstract class?
No, if there is any abstract method in a class, that class
must be abstract.
Can you use abstract
and final both with a method?
No, because abstract method needs to be overridden whereas
you can't override final method.
Is it possible to
instantiate the abstract class?
No, abstract class can never be instantiated.
What is interface?
Interface is a blueprint of a class that have static
constants and abstract methods.It can be used to achieve fully abstraction and
multiple inheritance.
Can you declare an
interface method static?
No, because methods of an interface is abstract by default,
and static and abstract keywords can't be used together.
Can an Interface be
final?
No, because its implementation is provided by another
class.
What is marker
interface?
An interface that have no data member and method is known
as a marker interface.For example Serializable, Cloneable etc.
What is difference
between abstract class and interface?
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Abstract class
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Interface
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1)An abstract class can have method body (non-abstract methods).
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Interface have only abstract methods.
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2)An abstract class can have instance variables.
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An interface cannot have instance variables.
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3)An abstract class can have constructor.
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Interface cannot have constructor.
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4)An abstract class can have static methods.
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Interface cannot have static methods.
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5)You can extends one abstract class.
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You can implement multiple interfaces.
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Can we define private
and protected modifiers for variables in interfaces?
No, they are implicitly public.
When can an object
reference be cast to an interface reference?
An object reference can be cast to an interface reference
when the object implements the referenced interface.
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