Java access modifiers

Java Access Modifiers
SCJP/OCJP exam objectives – 1.1,1.3,1.4

By,
Srinivas Reddy.S
www.JAVA9S.com

Access Modifiers - Importance

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Access Modifiers
• public
• protected
• default
• private

Access Modifiers - Importance
• Access modifiers helps to implement the
concept of encapsulation in OOPs.
• Encapsulation helps to hide the data and
behavior.
• Access Modifiers affect the accessibility at
two levels :
• Class
• Members(methods and instance variables)

Access Modifiers – at class level

public
• When a class is marked as public, it is visible to all
other classes which are inside and outside the
package. – Visible to everyone..

package com.java9s.Engines; package com.java9s.cars;
import com.java9s.Engines.Engine;
public class Engine{
public int engine1000cc(){ public class Ford{
int rpmCount=…..; void moveFast(){
return rpmCount; Engine e = new Engine();
} int rpm = e.engine3000cc()
public int engine3000cc(){ //move with speed related to
int rpmCount=…..; //rpm
return rpmCount; }
} }
}

public - class level
• A class marked as public is be accessible to all
classes in other packages, but should
mention the import statement.
• There is no need for an import statement
when a class inside the same package uses
the class marked as public

default – class level
• Default access has no key word.
• When there is no access modifier declared,
the access is default level access.
• The classes marked with default access are
visible only to the classes inside the same
package.

package com.java9s.bank;
class InterestRates{ When there is no
double creditCardInterest(){ access modifier specified
…….; - The access is default level
}

double homeLoanInterest(){
……;
} package com.java9s.bank;
} public class customerBanking{
double calculateHomeLoan(){
InterestRates i = new InterestRates();
double interest = i.creditCardInterest();
//calculate the home loan of customer
return x;
}
}

class InterestRates{
double creditCardInterest(){
…….;
}

double homeLoadInterest(){
……;
} package com.java9s.Customerbank;
The accessing class is not double interest = i.creditCardInterest();
in the same package. So, the class
With default will not be visible
return x;
}
}

protected and private – class level
***protected and private access modifiers are
not applicable to the class level
declaration***

Access modifiers – member level
(methods and instance variables)

public – member level
• A member with public access is visible to all
the classes inside and outside package.
• The class in which the member exists should
be is visible to the accessing class.

public class Engine{
return rpmCount; }
} }
}

•Check if the class itself is accessible
•Check if the import statement is used to import the class(if
accessed from other package)
•Finally- check if the member is accessible

class Engine{
return rpmCount; }
} }
}

The class engine is having default access and will not be visible to Ford

default – member level
• A member marked with default access will be
visible to the classes that are in the same
package.

default – member level
class InterestRates{
double creditCardInterest(){
…….;
}

double homeLoadInterest(){
……;
} package com.java9s.bank;
double interest = i.creditCardInterest();
return x;
}
}

protected – member level
• A member marked as protected is visible to
all classes in the same package(Just like
default).
• protected members are also accessible to
classes outside the package, but the
accessing class should be a subclass of the
member class.

protected- member level
package com.java9s.cars;
package com.java9s.cars;
public class Car{ public class Benz{
protected int speed; int move(){
} Car c = new Car();
package com.java9s.fastCars; return c.speed;
public class Ferrari extends Car{ }
int moveFast(){
return super.speed; }
}
int move(){ Note: The protected members can be
Car c= new Car(); accessed only by the subclasses in other
c.speed; packages and can invoke the members
only through inheritance mode.
}
Not by creating an instance.
}

private – member level
• When a member is marked as private, it is
only visible to other members inside the
same class.
• Other classes inside and outside the package
will not be able to access the private
members of a class.

private – member level

public class Car{
private String keyCode;
}

public class Theif{ keyCode variable is not
void steal(){ visible outside the class Car

Car c = new Car();
c.keyCode;
}
}

protected and private – class level
***protected and private access modifiers are
not applicable to the class level
declaration***

???

Access Modifiers - summary
Visibility public protected default private
From the same class Yes Yes Yes Yes

From a class in same package Yes Yes Yes No

From a class from outside the Yes No No No
package

From a subclass outside the Yes Yes(Only No No
package through
inheritance
mode)
From a subclass in the same Yes Yes Yes No
package

Access Modifiers – Local Variables
public class Calculator{
public int addition(int a, int b){
int c = a+b;
return c;
C is a local variable and only lives till the method
} Executes.

}

No access modifiers should be applied for Local variables

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Java access modifiers

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