2. Data Hiding
• 1 of the important OOP techniques
• Hiding the data within the class
• Making it available ONLY through the methods
• Also known as encapsulation
▫ It seals the data (and internal method) safely inside
the “capsule” of the class
▫ Can only be accessed by a trusted user (i.e. by the
method of the class)
3. Why need encapsulation?
• To hide the internal implementation details of the
class
• Can safely modified the implementation without
worrying breaking the existing code that uses the
class
• Protect class against accidental/ willful stupidity
• Keeps class tidy by keeping the visible fields to a
minimum
• Easier to use and understand
4. Access Control
• All the fields and methods of a class can always be
used within the body of the class itself.
• Java defines access control rules that restrict
members of a class from being used outside the
class.
• The public keyword, along with protected and
private, are accesscontrolmodifiers ; they specify
the access rules for the field or method.
5. Access to packages
• A package is always accessible to code defined within
the package.
• Whether it is accessible to code from other packages
depends on the way the package is deployed on the host
system.
• When the class files that comprise a package are stored
in a directory, for example, a user must have read access
to the directory and the files within it in order to have
access to the package.
• Package access is not part of the Java language itself.
• Access control is usually done at the level of classes and
members of classes instead
6. Access to classes
• By default, top-level classes are accessible within
the package in which they are defined.
• However, if a top-level class is declared public, it
is accessible everywhere (or everywhere that the
package itself is accessible).
7. Access to members
• By default, members are also accessible throughout
the package in which the class is defined.
• This default level of access is often called
packageaccess.
• The other three levels of access are defined by the
public, protected, and private modifiers.
8. example
// People can use this class.
public class Laundromat {
// They cannot use this internal field,
private Laundry[] dirty;
// but they can use these public methods
public void wash() { ... }
// to manipulate the internal field.
public void dry() { ... }
}
9. Access rules:
• If a member of a class is declared with the public modifier,
it means that the member is accessible anywhere the
containing class is accessible. This is the least restrictive type
of access control.
• If a member of a class is declared private, the member is
never accessible, except within the class itself. This is the
most restrictive type of access control.
• If a member of a class is declared protected, it is
accessible to all classes within the package (the same as the
default package accessibility) and also accessible within the
body of any subclass of the class, regardless of the package
in which that subclass is defined. This is more restrictive than
public access, but less restrictive than package access.
• If a member of a class is not declared with any of these
modifiers, it has the default package access: it is accessible to
code within all classes that are defined in the same package,
but inaccessible outside of the package.
10. Another example
The public methods are
the access points to this
class.s fields from the outside
java world.
Normally these methods are
referred as getters and
setters.
Therefore any class that
wants to access the variables
should access them through
these getters and setters.
12. Benefits of having encapsulation
• The fields of a class can be made read-only or write-
only
• A class can have total control over what is stored in
its fields
• The users of a class do not know how the class
stores its data.
• A class can change the data type of a fields, and a
users of the class do not need to change any of their
code
