public, private, protected and package
or default are four access modifier available in Java. These access
modifier provides Java programmer to control accessibility or visibility of
class, method or any field of class. Good understanding of public, private or
protected modifier is required in order to implement proper encapsulation
in Java and create a Java program which is easier to maintain. In this Java
tutorial we will see what is public, private, protected and default modifiers
are, which modifier can be used with top
level class and nested
class and what are difference
between public, private, protected and default modifier in Java. We In next
section we will discuss all four access modifier in decreasing order of
accessibility, starting from public which is most accessible and going down to
private which is least accessible.
Public vs Protected vs Package vs Private modifier in Java
In this section we will see each of these access modifier and learn about
them. Starting from public, which is least restrictive to private which is most
restrictive and provide highest form of encapsulation in Java.
Public
modifier in Java
public is most common and least
restrictive access modifier in Java. You can apply public modifier into
variables, methods and both top level and inner
classes in Java. Since public modifier offers least
amount of encapsulation its difficult to change, any publicly exposed API are
hard to change without breaking its client. So always put extra care while designing
public API means making your class, method or variable public in Java. Its not good
practice as well to make fields of a class public because it goes against encapsulation
and exposing internals of class removes any chance of improving internal
details with better performance alternative. That’s why its better to prefer
getter and setter method over public fields.Think twice before making
variables public in Java. So despite of most popular access modifier in test
environment, public should be used carefully in production
code. On syntactical front all interface methods are by default public in
Java.
Protected modifier in Java
protected access modifier is similar to public modifier and
can be applied to variables, methods and nested classes in Java. Though it has
two notable difference with public modifier. public variables
are accessible to everyone but protected variable is
only access inside subclass outside of package
it has declared. Second difference between public and protected modifier
is that unlike public modifier, protected modifier can
not be applied to top level class, Though you can still apply it to nested
or inner class in Java. protected method can be overridden
by any public or protected method and
only data which is supposed to be different for sub-class is made protected. Though
protected offers better encapsulation than public keyword
its still not the best form of encapsulation available and should be avoided as
much as possible. If you have a choice of making a variable, class or method
protected or public, choose protected.
Package or default access modifier
package level access is default access
level available to any Java class, method or variable. If you don't specify any
access modifier during variable or method declaration, Java compiler will
provide them package level access. It is also referred as package-private as any
variable which is package-private is only accessible inside that package.
Difference between protected and package level
access is that, It more restrictive than protected modifier
and its a default access level provided by Java. package level API are easier
to change than public API as it is most likely be developed by same person who is
developing other classes in package and you are sure that no client other than same
package are using it. If you have very good reason of modifying internals of
package level class you can do that with minimal changes , as all changes will
be confined up to package level only. Another difference between protected
and package modifier that package modifier can be used on top
level class as well.
Private access modifier
private access modifier is most
restrictive access modifier in Java and its Java best practice to make
variables, methods private by default. I have discussed this on why
should you make variables private in Java but major reason of this is solid
encapsulation provided by private keyword. private code is
easier to change and replace by better performance version.Its good policy to
declare interface
as public and keeping implementation private in Java.
Another important point about private access modifier is that
unlike public they are not accessible anywhere other than the class they
are declared. You can not apply private modifier on top level class
and private
method can not be overridden. Another interesting use of private modifier
is making constructor private to not allow external class to create instances
and instead force them to use static
factory methods. One of the popular example of private constructor is
Singleton pattern in Java , which makes it contractor private and instead
provide a getInstance() method which controls number of
instances.
That's all on What is public, protected, default (package private) and
private access modifier in Java and difference between public, private,
protected and package modifier. Access modifier is one of most important
fundamentals for any Java programmer and clever usage of access modifier is
required to build flexible and highly maintainable Java application. In short
use public, protect, default and private modifier carefully and if you are in
confusion make variables private.
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