03_A-OOPs_Interfaces.ppt
- 1. Session-3A
- 2. ● This module introduces patcipants to the java interface. ● Describes inheritence of interfaces ● creation of objects to interfaces. ● Abstract classes Module Overview 2
- 3. Interface An interface is an abstract data type that defines a list of abstract public methods that any class implementing the interface must provide. An interface can also include a list of constant variables and default methods. •Interface is defined with the interface keyword. • Interfaces cannot be instantiated directly. • An interface is not required to have any methods and may not be marked as final. •All nondefault methods in an interface are assumed to have the modifiers abstract and public in their definition. • All top-level interfaces are assumed to have public or default access, and they must include the abstract modifier in their definition. •Marking an interface as private, protected, or final will trigger a compiler error, since this is incompatible with these assumptions.
- 4. Interface //abstract method means unimplementation or no implementation public interface Person { public final static String country="India"; public abstract boolean isHospitalised();//unimplemented methods }
- 5. Interface Variables Interface variables rules: 1. Interface variables are assumed to be public, static, and final. Therefore, marking a variable as private or protected will trigger a compiler error, as will marking any variable as abstract. 2. The value of an interface variable must be set when it is declared since it is marked as final.
- 6. Interface Inheritence Inheritance rules when extending an interface: 1. An interface that extends another interface, as well as an abstract class that implements an interface, inherits all of the abstract methods as its own abstract methods. 2. The first concrete class that implements an interface, or extends an abstract class that implements an interface, must provide an implementation for all of the inherited abstract methods.
- 7. Inheritence example //abstract method means unimplementation or no implementation public interface Person extends PhysicallyChallenged,Resident{ public final static String country="India"; public abstract boolean isHospitalised();//unimplemented methods }
- 8. Default Method(java 8) A default method is a method defi ned within an interface with the default keyword in which a method body is provided. Contrast default methods with “regular” methods in an interface, which are assumed to be abstract and may not have a method body. A default method within an interface defi nes an abstract method with a default implementation. In this manner, classes have the option to override the default method if they need to, but they are not required to do so. If the class doesn’t override the method, the default implementation will be used.
- 9. Default Method Example public interface IsAdmitted{ boolean hasInsurance(); public default double getBill() { return 1000.0; } } Note:- methods of an interface are always public.
- 10. Default method rules 1. A default method may only be declared within an interface and not within a class or abstract class. 2. A default method must be marked with the default keyword. If a method is marked as default, it must provide a method body. 3. A default method is not assumed to be static, final, or abstract, as it may be used or overridden by a class that implements the interface. 4. Like all methods in an interface, a default method is assumed to be public and will not compile if marked as private or protected.
- 11. Static methods in Interface(java 8) Static methods are defi ned explicitly with the static keyword. There is one distinction between a static method in a class and an interface. A static method defi ned in an interface is not inherited in any classes that implement the interface. Here are the static interface method rules you need to be familiar with: 1. Like all methods in an interface, a static method is assumed to be public and will not compile if marked as private or protected. 2. 2. To reference the static method, a reference to the name of the interface must be used.
- 12. Static Method Example public interface Discharge{ static int no_Of_Days_Admit() { return 10; } }
- 13. Polymorphism Polymorphism is a oops feature in which the property of an object takes on many different forms. No of ways polymorphism achieved: Java object may be accessed using a reference with the same type as the object . Reference that is a superclass of the object, Reference that defi nes an interface the object implements, either directly or through a superclass. Explicit cast is not required if the object is being reassigned to a super type or interface of the object
- 14. Thank you.
Editor's Notes
- #3: Instructor Notes: