CS5000: Foundations of Programming. Mingon Kang, PhD Computer Science, Kennesaw State University

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1 CS5000: Foundations of Programming Mingon Kang, PhD Computer Science, Kennesaw State University

2 Interfaces Reference type (not a class) Collection of abstract methods

3 Interface declaration public interface Interface_name // any final, static fields // any abstract methods An interface is implicitly abstract Each methods is also implicitly abstract Abstract keyword is not necessary Methods are implicitly public

4 Interface declaration public interface Human public void eat(); public void sleep();

5 Implementing interfaces A class implements an interface Like signing a contract, agree to perform the specific behaviors of the interface. The class can declare itself as abstract when not specifying the interface A class uses implements keyword to implement an interface

6 Implementing interfaces public class Me implements Human public void eat() System.out.println( I eat ); public void sleep() System.out.println( I sleep ); public static void main(string[] args) Me m = new Me(); m.eat(); m.sleep();

7 Default Method Java8 introduces Default Method, which allows developer to add new methods to the interface without breaking the existing implementation of these interface Although concrete class fails to provide an implementation for the method, it provides flexibility to allow to use default method.

8 Default Method public interface oldinterface public void existingmethod(); default public void newdefaultmethod() System.out.println("New default method"); public class oldinterfaceimpl implements oldinterface public void existingmethod() // existing implementation is here public static void main(string[] args) oldinterfaceimpl o = new oldinterfaceimpl(); o.newdefaultmethod();

9 Interfaces A class can implement more than one interface at a time A class can extend only one class, but implement many interfaces An interface can extend another interface, similarly to the way that a class can extend another class.

10 Extending Interfaces public interface Sports public void sethometeam(string name); public void setvisitingteam(string name); public interface Football extends Sports public void hometeamscored(int points); public void visitingteamscored(int points); public void endofquarter(int quarter);

11 Extending Interfaces public interface Hockey extends Sports public void homegoalscored(); public void visitinggoalscored(); public void endofperiod(int period); public void overtimeperiod(int ot);

12 Extending Multiple Interfaces Interface can extend more than one parent interface public interface Hockey extends Sports, Event

13 Interface vs Class Interface is NOT a class Essentially a type that can be satisfied by any class that implements the interface. Abstract classes are meant to be inherited from Strong relationship between the two classes The relationship between the interface and the class implementing the interface is not necessarily strong

14 Interface vs Class Interfaces are a good substitute for multiple inheritance Abstract class can have some implementation code, while an interface cannot provide any method definitions

15 The Serializable interface An object can be represented as a sequence of bytes that includes the object's data In order to make a class serializable, simply add implements Serializable to the heading of the class definition public class SomeClass implements Serializable

16 The Serializable interface Classes that require special handling during the serialization and deserialization process must implement special methods with these exact signatures: private void writeobject(java.io.objectoutputstream out) throws IOException private void readobject(java.io.objectinputstream in) throws IOException, ClassNotFoundException; private void readobjectnodata() throws ObjectStreamException;

Abstract class & Interface

Islamic University of Gaza Faculty of Engineering Computer Engineering Department Computer Programming Lab (ECOM 2124) Lab 3 Abstract class & Interface Eng. Mohammed Abdualal Abstract class 1. An abstract