This document discusses interfaces and packages in Java. It defines an interface as a reference type that can contain only constants, method signatures, and nested types, with no method bodies. Interfaces are used to define common behaviors for unrelated classes. The document also defines packages as logical groupings of related classes and interfaces, and discusses how to create user-defined packages and control access to classes using access modifiers like public, private, and protected.

1. INTERFACE AND
PACKAGES
BCA 5th Sem
DEEPAK SHARMA
12KSSB6031

2. INTERFACE
 In the JAVA programming language, an Interface is
a reference type, similar to a class, that can contain only
constants, method signatures and nested types. There
are no method bodies. Interfaces cannot be instantiated,
they can only be implemented by classes or extended
by other Interfaces.
 Interfaces are used to code similarities which
classes of various type share, but do not necessarily
constitute a class relationship.

3. DEFINITION
Interface use for implementing multiple inheritance
Syntax of interface
interface interfacename
{
staticfinal variables;
abstract method;
}
Interface consists staticfinal variable and abstract methods.
Eg: interface i1
{
int i=5;
Float k=27.5;
void meth1(); // Abstract method
}

4. EXTENDING INTERFACE
 An interface can extend another interface, similarly to the
way that a class can extend another class.
 The extends keyword is used to extend an interface,
and the child interface inherits the methods of the parent
interface.
 Interface can be sub interfaced from other interfaces.
 A sub interface will inherit all members of super interface.

5. VARIOUS FORM OF IMPLEMENTING
INTERFACE
interface A
implements
class B
C
extends
class
A
interface
class class
B C
implements

6. A
B
C
D
E
class
extends
class
extends
class
implements
interface
extends
interface
interface
A B
extends
C
class D
interface
interface
implements

7. EXAMPLE INTERFACE PROGRAM
 public interface Area
 {
 final float pi=3.142;
 float compute(float x, float y);
 }
 public class Circle implements Area
 {
 public float compute(float x, float y)
 {
 return(pi*x*x);
 }
 }
 public class Rectangle implements Area
 {
 public float compute(float x, float y)
 {
 return(x*y);
 }
 }
Area
Compute
Circle Rectangle
Compute
implements
Compute

8. PACKAGES
DEFINITION:
 A Package is a logical organization of related classes.
The java classes can be logically organized into
packages.
 Packages is a collection of classes and interface.

9. USER DEFINED PACKAGES
 JAVA uses file system to manage packages, with each package
stored in its own directory.
 Package names are case sensitive. The directory name and
the package name should be the same.
 The classes declared within the package directory will belong to
the specified package.

10. HIDING CLASSES
The main advantage of packages is to hide the classes
from other packages, if we declare the class as public,
then the class is visible in all packages. If we do not
want the class to be public, the default access is used.
1.
package pack1;
public class ABC
{
-------;
}
2.
package pack1;
public class ABC{
}
class XYZ{
}

11. WHY DO WE NEED PACKAGES?
• One can easily determine that these types are
related.
• One knows where to find types that can provide
task-related functions.
• The names of your types won't conflict with the
type names in other packages because the
package creates a new namespace.
• One can allow types within the package to have
unrestricted access to one another yet still restrict
access for types outside the package.

12. ACCESS TO MEMBERS OF THE
CLASSES
private (default) protected public
The same class Yes Yes Yes Yes
Subclass in the package No Yes Yes Yes
Non-subclass in the package No Yes Yes Yes
Subclass in another package No No Yes Yes
Non-subclass in another package No No No Yes

13. ACCESS MODIFIER
package p1
class C1
public int x
class C3
C1 c1;
c1.x can be read or
modified
package p2
class C2 extends C1
x can be read or
modified in C2
class C4
C1 c1;
c1.x can be read nor
modified

14. THANK YOU