Interfaces in Java provide a common behavior that classes can implement. They declare public abstract methods and public static final variables. Classes that implement interfaces must define the interface's abstract methods but can determine how they are implemented. Interfaces allow for multiple inheritance by allowing classes to implement multiple interfaces and provide a consistent way for unrelated classes to share common behaviors.

1. Interfaces

2. Interfaces
• In Java, we can not only achieve Abstraction,
with the help Abstract classes but also with
the help of Interfaces.
• Interfaces provides a skeleton of a class.
• We can only declare public, static and final
variable in an Interface.
• All the methods declared in an Interface are
public and abstract.(a method without
implementation)

3. interface A {
int v1=1;
}// interfaces can be inherited
interface B extends A
{
int v2=2;
int sum=v2+A.v1;
}

4. Interfaces
• Interface provide a protocol of behaviour
• How the behaviour is implemented is the
responsibility of that Individual class.
• Keyword “implements” is used to apply any
interfaces on any class.
• Interfaces provide a mechanism to provide
multiple inheritance.

5. Example

6. Why Interfaces required?
• Interface allows us to implement common
behaviour in two different classes.
• Interfaces allows us to apply behaviours beyond
classes and class hierarchy.
• Consistent specification among unrelated classes.
• Reduce coupling between software component
• Applying multiple inheritance.
• Two or more classes may not achieve same
functionality.(No duplicity of class)
• Create richer classes.

7. Interfaces
• More than one interfaces can be implemented to
single class
• Keyword “interface” is used to declare an
interface.
• Syntactically an interface is declared same as a
class.
• However, interface variable can be only public,
static and final.
• We can’t create object of an Interface like
abstract class.

8. Syntax