Interfaces

1
Interfaces

• Outline
• Generic interface versus Java interface
• What a (Java) interface is
• Its syntax
• What it says
• What it does NOT say
• How it is used, why it is useful
• How interfaces are used in WordGames
• UML class diagram for WordGames
• WordGames
• An application of interfaces

2
Generic interfaces

• Generic computer-science interface
• The face that one entity shows others
• What services it provides
• What information it expects
• Physical examples
• Computer Interfaces
• Stethoscope
• Telephone
• Camera
• Toaster

3
Why have interfaces?

• A Java interface is the face that one class
  shows others
• An interface contains the signature but not body
  for each method
• Any class that implements an interface must
  provide the methods listed in the interface
• So an interface specifies a contract

public interface ClockRadio public Time
getTime() public void setTime(Time x)
public void setTime(Time x, Station s)
Example of a Java interface
4
Why have interfaces?
public interface ClockRadio public Time
getTime() public void setTime(Time x)
public void setTime(Time x, Station s)

• Java interfaces are important because
• They provide for software reuse. For example
• I provide a StringTransformable interface
• You provide classes that implement
  StringTransformable
• Our separately-written code works together
  seamlessly!
• They provide genericity. For example
• My code declares each of your things as a
  StringTransformable thing
• You provide various implementations of
  StringTransformable
• e.g. Capitalizer, NameDropper, UbbyDubber,
• My code is generic it doesnt care what
  implementation of StringTransformable you supply!

Interfaces can (and should) be used as types
5
UML class diagram for WordGames
All our stuff
The StringTransformable interface is how our code
knows how to connect to your code
ltltinterfacegtStringTransformable -----------------
---------- transform(String) String
Capitalizer
NameDropper
xxx
xxx

Questions on this important idea?
6
Java InterfacesSummary
public interface ClockRadio public Time
getTime() public void setTime(Time x)
public void setTime(Time x, Station s)

• A Java interface is the face that one class
  shows others
• An interface contains the signature but not body
  for each method
• Any class that implements an interface must
  provide the methods listed in the interface
• So an interface provides a contract
• Java interfaces are important because they
  provide for
• Software reuse
• Genericity

From now on, interface means Java interface
to us