Lecture Objectives Learn what is an ADT, why is it useful Understand algorithm efficiency Use...

CS 340

Lecture Objectives

Learn what is an ADT, why is it useful Understand algorithm efficiency Use Eclipse for coding and testing Understand and use method

overloading, overriding Find out why polymorphism is useful in

software design

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ADTs or… Abstract Data Types

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ADTs

Abstract Date Type (ADT)

An encapsulation of data and methods

Allows for reusable code

The user need not know about the implementation of the ADT

A user interacts with the ADT using only public methods

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ADTs (cont.)

ADTs facilitate storage, organization, and processing of information

Such ADTs often are called data structures

The Java Collections Framework provides implementations of common data structures

Other reasons for the ADTs to exist?

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Interfaces

An interface specifies or describes an ADT to the applications programmer: methods and actions ADTs must perform what arguments, if any, must be passed to

each method what result the method will return

The interface can be viewed as a contract which guarantees how the ADT will function

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Interfaces (cont.)

A class that implements the interface provides code for the ADT

If implementation satisfies the ADT contract, then Programmer may implement it as he or she

chooses The programmer may add:

data fields not in the implementation methods not in the implementation constructors

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Example: smartPhone Interface An smartPhone is...

It must provide operations to: wake up/sleep allow the user to open a particular

application add contact display messages adjust volume

A class that implements an smartPhone must provide a method for each operation

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Example: smartPhone Interface (cont.)

It must provide operations to: wake up/sleep allow the user to

open a particular application

add contact display messages adjust volume

public interface smartPhone {

}

Interface ___Code

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}

Interface ___Code

The keyword interface in the header indicates

that an interface is being declared

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/** Wakes up after it verifies a user's PIN.

@param pin The user's PIN

@return success or failure

*/

boolean wakeUp(String pin);

boolean sleep();

}

Interface ___Code

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It must provide operations to: wake up/sleep allow the user

to open a particular application



/** Allows the user to open an application.

@param app The selected application

@param success Whether or not the application opened*/

void openApplication(String app, boolean success);

}

Interface ___Code

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/** Allows the user to add a contact

@param name

@param phone numbers*/

void addContact(String name, int mobile, int home, int office, int other);

}

Interface ___Code

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add contact display

messages adjust volume


/** Allows message to be displayed

@param message to be printed*/

void printMessage(String message);

}

Interface ___Code

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/** Allows the user to change volume

@param message to be printed

@return success or fail*/

boolean changeVolume(int change);

}

Interface ___Code

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Interfaces (cont.)

Shows only headings for its methods These are considered abstract methods Abstract methods must be defined in a

class that implements the interface

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Interface Definition

FORM:

public interface interfaceName { abstract method headings constant declarations}

EXAMPLE:

public interface Payable { public abstract double calcSalary(); public abstract boolean salaried(); public static final double DEDUCTIONS = 25.5;}

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The implements Clause

Here is a class that implement an interface:

public class smartPhoneiPhone implements smartPhonepublic class smartPhoneDroid implements smartPhone

A class may implement more than one interface—their names are separated by commas

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The implements Clause: Pitfalls Syntax error:

Class smartPhoneDroid should be declared abstract; it does not define method printMessage(String) in interface smartPhone

If a class contains an undefined abstract method, then It needs to be declared as an abstract class

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The implements Clause: Pitfalls (cont.)

You cannot instantiate an interface:

smartPhone asmartPhone = new smartPhone();

// invalid statement

Doing so will cause a syntax error:

interface smartPhone is abstract; cannot be instantiated

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Declaring a Variable of an Interface Type

You can declare a variable that has an interface type

/* expected type */smartPhoneDroid ATM0 = new smartPhoneDroid();

/* interface type */smartPhone ATM1 = new smartPhoneDroid();smartPhone ATM2 = new smartPhoneiPhone();

The reason for wanting to do this will become clear when we discuss polymorphism

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Create a music library for myTunes store

Include ratings and prices

Eclipse

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myStore (we sell songs online)

23Method Overriding, Method Overloading, Polymorphism

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Method Overriding

Returning to the Robot example, if we declare and then run:

Robot myRobot = new Computer("Asimo", "Intel", 5, 16000, 200.4);

Cylon yourRobot = new Cylon(“Toaster", "AMD", 5, 24000, 1000.8, 5000.0, 7.5);

System.out.println("My computer is:\n" + myRobot.toString());

System.out.println("Your computer is:\n" + yourRobot.toString());

What is the output?

Cylon

double pixelsdouble battleSpeed

Robot

String manufacturerString processorint diskSizeint numberOfPartsdouble processorSpeed

int getDiskSize()double getProcessorSpeed()int getParts()String toString()

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Method Overriding (cont.)

The output would be:My Robot is:Manufacturer: AsimoCPU: IntelBody parts: 5Disk: 16000 gigabytesSpeed: 200.4 gigahertz

Your Robot is:Manufacturer: ToasterCPU: AMDBody parts: 5Disk: 24000 gigabytesSpeed: 1000.8 gigahertz The pixels and battleSpeed

variables are not printed because Cylon has not defined a toString() method

Cylon


Robot



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To define a toString() for Cylon:public String toString() { String = result = super.toString() + "\nPixels: " + pixels + "\nSpeed in battle: " +

battleSpeed + " shots/sec"; return result; }

Now Cylon's toString() method will override Robot's inherited toString()method and will be called for all Cylon objects Cylon


Robot



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To define a toString() for Cylon:public String toString() { String = result = super.toString() + "\nPixels: " + pixels + "\nSpeed in battle: " +

battleSpeed + " shots/sec"; return result; }

Now Cylon's toString() method will override Robot's inherited toString()method and will be called for all Cylon objects


super.methodName()

Using the prefix super in a call to a method methodName calls the method with that name in the superclass of the current class

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Cylon


Robot



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Method Overloading

Methods with the same name, return type, and parameters override corresponding inherited methods

Methods with the same name but different parameters are overloaded

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Method Overloading (cont.) Take, for example, our Cylon constructor: public Cylon(String man, String processor, int parts, int

disk, double procSpeed, int pixels, int battleSpeed) {

. . .

}

If we want to have a default manufacturer for a Cylon, we can create a constructor with six parameters instead of seven

public Cylon(String processor, double ram, int disk, double procSpeed, double screen, double wei) {

this(DEFAULT_NB_MAN, double ram, int disk, double procSpeed, int pixels, int battleSpeed);

}

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This call invokes the seven-parameter constructor passing on

the six parameters in this constructor, plus the default

manufacturer constant DEFAULT_NB_MAN

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Method Overloading: Pitfall

When overriding a method, the method must have: same name the same number and types of parameters in the same order

If not, the method will overload This error is common

SOLUTION: the annotation @Override @Overridepublic String toString() { . . .}

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Polymorphism

Polymorphism means having many shapes

Polymorphism is a central feature of OOP

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Polymorphism (cont.)

For example: You write a program to reference robots, You need a variable to reference a Robot or

a Cylon Easy!

Robot theRobot; can reference either a Robot or a Cylon—because a Cylon is-a Robot!

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Polymorphism (cont.)

Example:theRobot = new Cylon(“Centurion", "Intel", 4, 240, 6, 15000, 5000);

System.out.println(theRobot.toString());

Which toString() method will be called, Robot's or Cylon's?

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Cylon


Robot



Lecture Objectives Learn what is an ADT, why is it useful Understand algorithm efficiency Use...

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