Java Access Modifiers

                        Introduction to Java Access Modifiers

The access to classes, constructors, methods and fields are regulated using access modifiers i.e. a class can control what information or data can be accessible by other classes. To take advantage of encapsulation, you should minimize access whenever possible.

Java provides a number of access modifiers to help you set the level of access you want for classes as well as the fields, methods and constructors in your classes. A member has package or default accessibility when no accessibility modifier is specified.

Java comes with four access specifiers. They are

1. public
2. protected
3. default
4. private

I) Class level access modifiers (java classes only)

Only two access modifiers is allowed, public and no modifier

• If a class is ‘public’, then it CAN be accessed from ANYWHERE.
• If a class has ‘no modifer’, then it CAN ONLY be accessed from ‘same package’.

II) Member level access modifiers (java variables and java methods)

All the four public, private, protected and no modifer is allowed.

• public and no modifier – the same way as used in class level.
• private – members CAN ONLY access.
• protected – CAN be accessed from ‘same package’ and a subclass existing in
  any package can access.

 For better understanding, member level access is formulated as a table:

Access Modifiers	Same Class	Same Package	Subclass	Other packages
public	Y	Y	Y	Y
protected	Y	Y	Y	N
no access modifier(default)	Y	Y	N	N
private	Y	N	N	N

First row {public Y Y Y Y} should be interpreted as:

• Y – A member declared with ‘public’ access modifier CAN be accessed by the members of the ‘same class’.
• Y – A member declared with ‘public’ access modifier CAN be accessed by the members of the ‘same package’.
• Y – A member declared with ‘public’ access modifier CAN be accessed by the members of the ‘subclass’.
• Y – A member declared as ‘public’ CAN be accessed from ‘Other packages’

Second row {protected Y Y Y N} should be interpreted as:

• Y – A member declared with ‘protected’ access modifier CAN be accessed by the members of the ‘same class’.
• Y – A member declared with ‘protected’ access modifier CAN be accessed by the members of the ‘same package’.
• Y – A member declared with ‘protected’ access modifier CAN be accessed by the members of the ‘subclass’.
• N – A member declared with ‘protected’ access modifier CANNOT be accessed by the members of the ‘Other package’.

similarly interpret the access modifiers table for the third (no access modifier) and fourth (private access modifier) records.