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TitleCore Java
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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- public classes, methods, and fields can be accessed from everywhere.
• Protected- 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.

• Default(no specifier)- 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.

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• 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.

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 Classes- A final class cannot have subclasses.
• final Variables- A final variable cannot be changed once it is initialized.
• final Methods- A final method cannot be overridden by subclasses.

41.What are the uses of final method?

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;

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