msc it programming methodology (2). number name number

MSc IT

Programming Methodology (2)

number

namenumber

namenumber

balance

abbey

namenumber

balance

namenumber

balance

abbey

deposit

abbey

deposit withdraw

abbey

getBalance

deposit withdraw

abbey

getBalance

deposit withdraw

abbey

BankAccount

abbey

BankAccount

abbeyhalifax

BankAccount

Class

abbeyhalifax

Class

objectobject

Classes and objects

Learning objectives

• explain the meaning of the term object-oriented;

• explain the concept of encapsulation;

• explain the terms class and object;

• create objects in Java;

• call the methods of an object;

• Use a number of methods of the String class;

• create and use arrays of objects.

Object-oriented programming…

Classes….

Student

data

methods

Class

objects

?

s1

s2

s3

s4

Student

data

methods

Class

objects

?

s1

s2

s3

s4

Encapsulation:

The hiding of data within a class

How do you create objects from a Class ?

Object creation is a two-step process:

STEP 1:Declare object type.

Student

data

methods

? s1

s1; Student

Class

object

The effect on computer memory of declaring an object……

Student s1 ;

Computer Memory Java Instructions

s1

? Reference variable

Student s1 ;

Computer Memory Java Instructions

s1

null Reference variable

STEP 2:Allocating memory to store the object data!

This is sometimes called instantiating an object!

Student

data

methods

?

Class

s1

objectStudent( )String, String

A constructor method is required to generate object data from a classs1 = new Student ( );“071202”, “Kans”

The effect on computer memory of instantiating an object……

Student s1 ;

Computer Memory Java Instructions

s1

This is the space for the new Student

object

s1 = new Student (“071202”, “Kans”);

null

You can combine steps 1 & 2!

s1Student

s1 = new Student ( “071202”, “Kans”);

; = new Student (”071202”, “Kans”);

You can instantiate many objects from one Class !

Robot

?

moveRight(int)

moveLeft(int)

moveUp(int)

moveDown(int)

Robot( ) int, int

Robot r1;

r1 = new Robot(5, 50);

Robot r2;

r2 = new Robot(10, 2);

Calling the methods of another class….

Robot

?

moveRight(int)

moveLeft(int)

moveUp(int)

moveDown(int)

Robot( ) int, int

Robot r1;

r1 = new Robot(5, 50);

Robot r2;

r2 = new Robot(10, 2);

Robot

?

moveRight(int)

moveLeft(int)

moveUp(int)

moveDown(int)

Robot( ) int, int

Robot r1;

r1 = new Robot(5, 50);

Robot r2;

r2 = new Robot(10, 2);

r1.moveRight(20);

r2.moveDown(25);

Revisiting the Scanner

class ……

To create a Scanner object we call the Scanner constructor:

Scanner sc = new Scanner (System.in);

Scanner methods…..

int x = sc.nextInt();

double y = sc.nextDouble();

char reply = sc.next().charAt(0);

this is a String methodthis is a String object

The String class

The String class is different from all other classes in Java.

We can create String objects without a call to a constructor:

String day = “Wednesday”; new String (“Wednesday”);

To obtain a string from the keyboard you can use the next method of Scanner

day = sc.next();

String methods ……

charAt

Accepts an integer and returns the character at that position in the string. Note that indexing starts from zero, not 1!

An item of type

int

An item of type

char

length Returns the length of the string .

None An item of type

int

substring Accepts two integers (eg m and n) and returns a copy of a chunk of the string, from position m to position n-1.

Two items of type

int

A String

object

concat Accepts a string and returns a new string consisting of the that string joined to the end of the original string.

A String

object

A String

object

Method Description Inputs Output

toUpperCase

Returns a copy of the original string, all upper case.

None A String object

toLowerCase Returns a copy of the original string, all lower case.

None A String object

compareTo

Accepts a string and compares it to the object's string. It returns zero if the strings are identical, a negative number if the object's string comes first in the alphabet, and a positive number if it comes later.

A String object

An item of type

int.

equals Accepts an object and compares this to this to the string. It returns true if these are identical, otherwise returns false.

An object of any class

A boolean

value.

Method Description Inputs Output

import java.util.*;

public class StringTest

{

public static void main(String[ ] args)

{

Scanner sc = new Scanner(System.in);

String str = new String();

System.out.print("Enter a string: ");

str = sc.next();

System.out.println("The length of the string is " + str.length());

System.out.println("The character at position 3 is " + str.charAt(2));

System.out.println("Characters 2 to 4 are " + str.substring(1,4));

System.out.println(str.concat(" was the string entered"));

System.out.println("This is upper case: " + str.toUpperCase());

System.out.println("This is lower case: " + str.toLowerCase());

}

}

;

Enter a string: Europe

The length of the string is 6

The character at position 3 is r

Characters 2 to 4 are uro

Europe was the string entered

This is upper case: EUROPE

This is lower case: europe

RUN

import java.util.*;

public class StringTest

{

public static void main(String[] args)

{

Scanner sc = new Scanner(System.in);

String str = new String();

System.out.print("Enter a string: ");

str = sc.next();

System.out.println("The length of the string is " + str.length());

System.out.println("The character at position 3 is " + str.charAt(2));

System.out.println("Characters 2 to 4 are " + str.substring(1,4));

System.out.println(str.concat(" was the string entered"));

System.out.println("This is upper case: " + str.toUpperCase());

System.out.println("This is lower case: " + str.toLowerCase());

}

}

Comparing strings …..

When checking two strings for equality use the equals method!

Do not use the equality operator (==)

if(firstString == secondString){ // more code here}

String firstString = “Hello”;

String secondString = “Goodbye”;

if(firstString == secondString){ // more code here}

String firstString = “Hello”;

String secondString = “Goodbye”;

if(firstString.equals(secondString)){ // more code here}

String firstString = “Hello”;

String secondString = “Goodbye”;

if(firstString.equals(secondString)){ // more code here}

String firstString = “Hello”;

String secondString = “Goodbye”;

When comparing two strings alphabetically use the compareTo method!

import java.util.*;

public class StringComp

{

public static void main(String[ ] args)

{

Scanner sc = new Scanner(System.in);

String string1, string2;

int comparison;

System.out.print("Enter a String: ");

string1 = sc.next();

System.out.print("Enter another String: ");

string2 = sc.next();

comparison = string1.compareTo(string2);

// check comparison

}

}

if (comparison < 0)

{

System.out.println(string1 + " comes before " + string2

+ " in the alphabet");

}

else if (comparison > 0)

{

System.out.println(string2 + " comes before " + string1

+ " in the alphabet");

}

else

{

System.out.println("The strings are identical");

}

RUN

Enter a String:

Enter another String:

goodbye comes before hello in the alphabet

hello

goodbye

Using some classes written for you

Using some classes written for you

Oblong

Using some classes written for you

Oblong

EasyScanner

Using some classes written for you

Oblong

EasyScanner

BankAccount

Oblong

public class RectangleCalculations{ public static void main(String[ ] args) {

double length, height;// code to get length and heightSystem.out.println(“Area = " + area(length,height) ); System.out.println(“Perimeter = " +

perimeter(length,height) );

private static double area (double lengthIn, double heightIn) {

return lengthIn * heightIn; }

private static double area (double lengthIn, double heightIn) {

return 2* (lengthIn * heightIn_; }}

public class RectangleCalculations{ public static void main(String[ ] args) {

double length, height;// code to get length and heightSystem.out.println(“Area = " + area(length,height) ); System.out.println(“Perimeter = " +

perimeter(length,height) ); }

private static double area (double lengthIn, double heightIn) {

return lengthIn * heightIn; }

private static double area (double lengthIn, double heightIn) {

return 2* (lengthIn + heightIn); }}

Methods of the Oblong class..

Oblong

Oblong myOblong

12.5

20

= new Oblong(12.5, 20);

setLength

myOblong.setlength(17.5);

12.5

20

17.5

setHeight

myOblong.setHeight(12);

20

17.5

12

getHeight

System.out.println( );

17.5

12

myOblong.getHeight( )

getLength

System.out.println( );

17.5

12

myOblong.getLength( )

calculateArea

System.out.println( );

17.5

12

myOblong.calculateArea( )

calculatePerimeter

System.out.println( );

17.5

12

myOblong.calculatePerimeter( )

Issues with using the Scanner class for keyboard input….

• it is necessary to create a new Scanner object in every method that uses the Scanner class;

• there is no simple method such as nextChar for getting a single character like there is for the int and double types;

• the next method doesn't allow us to enter strings containing spaces.

The EasyScanner class resolves these problems!

The input methods of the EasyScanner class

Java type EasyScanner method

int nextInt()

double nextDouble()

char nextChar()

String nextString()

To use the methods of EasyScanner we do not need to create an object!

char c;

System.out.print("Enter a character: ");

c = EasyScanner.nextChar();

String s;

System.out.print("Enter a string: ");

s = EasyScanner.nextString();

The BankAccount class ….

The BankAcount class contains methods to process a bank account.

BankAccount

99786754Susan Richards

500.0

46376205 Sumana Khan

150.0

The methods of the BankAccount classMethod Description Inputs Output

BankAccount A constructor. It accepts two strings and assigns them to the account number and account name respectively. It also sets the account balance to zero.

Two String objects

Not applicable

getAccountNumber Returns the account number. None An item of type String

getAccountName Returns the account name. None An item of type String

getBalance Returns the balance. None An item of type double

deposit Accepts an item of type double and adds it to the balance

An item of type double

None

withdraw Accepts an item of type double and subtracts it from the balance

An item of type double

None

public class BankAccountTester

{

public static void main(String[ ] args)

{

BankAccount account1

= new BankAccount("99786754","Susan Richards");

account1.deposit(1000);

System.out.println("Account number: "

+ account1.getAccountNumber());

System.out.println("Account name: " +

account1.getAccountName());

System.out.println("Current balance: " + account1.getBalance());

}

}

Account number: 99786754

Account name: Susan Richards

Current balance: 1000.0

Arrays of objects ..

int[] someArray = new int[3];

An array of 3 integers

An array of 3 BankAccount objects

BankAccount[] accountList= new BankAccount[3];

The effect on memory of creating an array of objects …

null

null

null

accountList

accountList

= new BankAccount [3];

reference to bank account

reference to bank account

reference to bank account

Java instructionComputer memory

BankAccount[] accountList;

null

Adding bank accounts to the array …

accountList[0] = new BankAccount("99786754","Susan Richards");

accountList[1] = new BankAccount("44567109","Delroy Jacobs");

accountList[2] = new BankAccount("46376205","Sumana Khan");

accountList[1]

BankAccountwith account number

"46376205" and name "Sumana Khan"

accountList[2]

accountList[0]

BankAccount with account number "99786754" and name

"Susan Richards"

BankAccount with account number "44567109" and name

"Delroy Jacobs"

accountList

Accessing objects in an array ….

accountList[0].deposit(1000);

returns a BankAccount object

calls a BankAccount method

accountList[0].withdraw(500);

accountList[2].deposit(150);

public class BankAccountTester2

{

public static void main(String[ ] args)

{

BankAccount[ ] accountList = new BankAccount[3];

accountList[0] = new BankAccount("99786754","Susan Richards");

accountList[1] = new BankAccount("44567109","Delroy Jacobs");

accountList[2] = new BankAccount("46376205","Sumana Khan");

accountList[0].deposit(1000);

accountList[2].deposit(150);

accountList[0].withdraw(500);

for(BankAccount item : accountList)

{

System.out.println("Account number: " + item.getAccountNumber());

System.out.println("Account name: " + item.getAccountName());

System.out.println("Current balance: " + item.getBalance());

System.out.println();

}

}

}

Account number: 99786754

Account name: Susan Richards

Current balance: 500.0

Account number: 44567109

Account name: Delroy Jacobs

Current balance: 0.0

Account number: 46376205

Account name: Sumana Khan

Current balance: 150.0

Practical Work

Follow these steps to make use of classes written for you (such as Oblong and EasyScanner)..

First, go to this module’s web site and download the classes we have written for you..

Now, every time your program needs to use a file (such as Oblong), add it to your project!

This program needs access to the Oblong class

Right click your project (or choose Project from the menu)

Choose Add >Add Exisiting Files

Select the file(s) you need.

You will be asked if you want this file to be added into your project or kept outside.

Select Add to add the file into your project.

File has been added and your program will now compile!

Remember the programs you write should not have the same name as our files!

public class TestOblong

{

public static void main (String[ ] args)

{

Oblong ob1 = new Oblong (4.2, 10);

System.out.println("area = " + ob1.calculateArea());

System.out.println("permeter = " + ob1.calculatePerimeter());

}

}

public class TestOblong

{

public static void main (String[ ] args)

{

Oblong ob1 = new Oblong (4.2, 10);

System.out.println("area = " + ob1.calculateArea());

System.out.println("permeter = " + ob1.calculatePerimeter());

}

}

public class TestOblong

{

public static void main (String[ ] args)

{

Oblong ob1 = new Oblong (4.2, 10);

System.out.println("area = " + ob1.calculateArea());

System.out.println("permeter = " + ob1.calculatePerimeter());

}

}

public class TestOblong

{

public static void main (String[ ] args)

{

Oblong ob1 = new Oblong (4.2, 10);

System.out.println("area = " + ob1.calculateArea());

System.out.println("permeter = " + ob1.calculatePerimeter());

}

}

area = 42.0

area = 42.0

public class TestOblong

{

public static void main (String[ ] args)

{

Oblong ob1 = new Oblong (4.2, 10);

System.out.println("area = " + ob1.calculateArea());

System.out.println("perimeter = " + ob1.calculatePerimiter());

}

}

public class TestOblong

{

public static void main (String[ ] args)

{

Oblong ob1 = new Oblong (4.2, 10);

System.out.println("area = " + ob1.calculateArea());

System.out.println("perimeter = " + ob1.calculatePerimiter());

}

}

area = 42.0

perimeter = 28.4

Design and implement a program that performs in the following way:

• when the program starts two bank accounts are created, using names and numbers which are written into the code;

• the user is then asked to enter an account number, followed by an amount to deposit in that account;

• the balance of the appropriate account is then updated accordingly – or if an incorrect account number was entered a message to this effect is displayed;

• the user is then asked if he or she wishes to make more deposits;

• if the user answers 'y' (for yes), the process continues;

• if the user answers 'n' (for no), then both account details (account number, account name and balance) are displayed.

***Bank Program***

Which bank account?:

***Bank Program***

Which bank account?: a123

***Bank Program***

Which bank account?: a123

How much to deposit?

***Bank Program***

Which bank account?: a123

How much to deposit? 250

***Bank Program***

Which bank account?: a123

How much to deposit? 250

More deposits?

***Bank Program***

Which bank account?: a123

How much to deposit? 250

More deposits? n

***Bank Program***

Which bank account?: a123

How much to deposit? 250

More deposits? n

number: a123 name: Aaron balance: 250.0

number: a456 name: Obama balance: 0.0