java with xoh for exams

JAVA WITH XOH FOR EXAMS

XS MAPHUMULO

***Java guide***

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Copyright © 2015 X.S. Maphumulo

Publishers and Copyright laws

No part of this publication may be reproduced, stored in a retrieval

system, or transmitted, in any form, or by any means, electronic,

mechanical, photocopying, recording, or otherwise, without the prior

consent of the publisher.

For modifications contact the author

Email: [email protected] or [email protected]

Contact number: 0612375781

mailto:[email protected]

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The Author

Xolani Samkelo Maphumulo, author of this hands-on java guide, is a

first year student in Computer Science at the University of the Free State. He lives

in Durban and he has been a java basic coder for 3 years in Zwelibanzi High school

situated in Durban. He is an excellent junior coder in both languages C# and java

and He feels so incline to share his knowledge with matriculates of 2015 for the

upcoming final exams.

Acknowledgements

I would like to express my greatest gratitude to my high school teachers MN

Ngwane and KC Ngcobo (IT educators), for giving me the best and pure

programming skills in java. Also a special thanks to the sole editor,

Khang Mokoena.

Who is this guide for, what does it cover and

what you need in order to use it

This guide is designed specifically for current matriculates as a tool to get them on

the road for the upcoming final examination in Information Technology Paper 1.I

do not teach you the syntax of the java language but I teach how to program, so

follow as I do the previous past papers using different approaches. The guide also

consists of complex exercises that will prepare you for the exam and the solutions

are provided at the end of the book. Netbeans 7.3.1 is used to compile all the

solutions included but other versions will also support the source code of each

question. Variable’s names and controls such as buttons are changed according to

a naming convention specified in APPENDIX A.

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CONTENT

The content is structured according to the order of questions in the

final exam paper.

Section A – General Programming skills

String class methods: format, split, substring, char At and Exceptions and

string handling

Writing complex mathematical formulas using arithmetic operators and

Math class methods: random, round, power etc.

Associate different (not restricted to default) events to GUI components.

Using Programming techniques for problem solving, such as loops, date

functions and casting.

Section B -OOP

Object Oriented Programming(OOP) and Advanced OOP

1. Applying objects ,methods and classes

2. Inheritance ,Encapsulation and Polymorphism

Section C Problem solving

Arrays in 1 dimensional and 2D

Reading ,Writing and Manipulation of Text Files

String manipulation

Dynamic instantiation of objects

Solutions

Appendix A – Naming conventions, data types, Access modifiers and escape

characters

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SECTION A

Composed of question 1!

General programming skills

To use string classes in complex problems

To use math classes and format your output

To apply programming techniques such as loops

And defensive programming.

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Introduction

The String classes and handling

Java Class Library (JCL) includes a huge library of codes and predefined classes of

which, we as developers use in order to solve problems. This Library (JCL) also

contains string classes and methods such as format,split,substring ,char At and

some defensive programming statements that are used to handle string and

prevent runtime errors.

Since this is just a guide, I will not explain in detail about JCL classes but will explain

those that I will use in my source code. For those who want to dig further browse

the link: https://en.wikipedia.org/wiki/Java_Class_Library Summary of strings methods

The prefixed data type indicate indicates the return value

Use the link below to download solutions to all the questions included

in this guide, however they are provided at the end of the book.

http://www.datafilehost.com/d/1dfe90c8

“Whether you want to uncover the secrets of the

universe, or you want to pursue a career in the 21st

century, Basic computer programming is an

essential skill to learn”

~ Stephen Hawking

https://en.wikipedia.org/wiki/Java_Class_Library

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String classes and methods

char charAt (int index): It returns the character at the specified index. Specified

index value should be between 0 to length () -1 both inclusive.

boolean equals(Object obj): Compares the string with the specified string and

returns true if both matches else false.

boolean equalsIgnoreCase(String string): It works same as equals method but it

doesn’t consider the case while comparing strings. It does a case insensitive

comparison.

int compareTo(String string): This method compares the two strings based on the

Unicode value of each character in the strings.

int compareToIgnoreCase(String string): Same as CompareTo method however it

ignores the case during comparison.

boolean startsWith(String prefix, int offset): It checks whether the substring

(starting from the specified offset index) is having the specified prefix or not.

int lastindexOf(String str): Returns the index of last occurrence of string str.

String substring(int beginIndex): It returns the substring of the string. The substring

starts with the character at the specified index.

String substring(int beginIndex, int endIndex): Returns the substring. The substring

starts with character at beginIndex and ends with the character at endIndex.

String replace(char oldChar, char newChar): It returns the new updated string after

changing all the occurrences of oldChar with the newChar.

boolean contains(CharSequence s): It checks whether the string contains the

specified sequence of char values. If yes then it returns true else false.

int length(): It returns the length of a String

String toUpperCase(): Equivalent to toUpperCase(Locale.getDefault()).

String toLowerCase(): Equivalent to toLowerCase(Locale. getDefault()

http://beginnersbook.com/2013/12/java-string-charat-method-example/

http://beginnersbook.com/2013/12/java-string-equals-and-equalsignorecase-methods-example/

http://beginnersbook.com/2013/12/java-string-equals-and-equalsignorecase-methods-example/

http://beginnersbook.com/2013/12/java-string-compareto-method-example/

http://beginnersbook.com/2013/12/java-string-comparetoignorecase-method-example/

http://beginnersbook.com/2013/12/java-string-startswith-method-example/

http://beginnersbook.com/2013/12/java-string-lastindexof-method-example/

http://beginnersbook.com/2013/12/java-string-substring-method-example/

http://beginnersbook.com/2013/12/java-string-substring-method-example/

http://beginnersbook.com/2013/12/java-string-replace-replacefirst-replaceall-method-examples/

http://beginnersbook.com/2013/12/java-string-length-method-example/

http://beginnersbook.com/2013/12/java-string-tolowercase-method-example/

http://beginnersbook.com/2013/12/java-string-tolowercase-method-example/

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Math classes

In computational problems these classes come in handy. The table below shows

the commonly used methods. There are many more than these ones provided but

some of them are beyond the scope of your curriculum.

Method Description Example abs(x) Absolute value of x int numb= Math.abs(-5);

//=5

exp(a) Gives ea Double ex = Math.exp(1); // =2.71

max(x,y) Largest of arguments x and y

Int max =Math.max(3,4); //=4

min(x,y) Smallest of arguments ,x and y

Int min =Math.min(3,4); //=3

pow(a,b) Gives ab double pwr=Math.pow(2,5); //=32

round(x) Nearest integer to x double n=Math.round(13.6); //=14

sqrt(x) Square root of x double sqrt =Math.sqrt(25); //=5

Reference

1) Marietjie Havenga & Christina Moraal,

(2007),Creative programming in java part 2 ,BitaByte

PTY (ltd)

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The following statements are used when making a decision and also in

defensive programming which is covered in section C.

If-else statement

If-else statement is the crucial tool used for validation and error

checking.

Code segment If (Boolean condition)

{

Body of the program if the Boolean condition is true

}

else

{

Body of the program if the Boolean condition is false

}

A Boolean condition is any statement that only returns true or

false. For instance, marks>=50 the result will be true only if the

marks is greater or equivalent to 50, else false .An if- statement

may contain a compound boolean condition :

if ((marks>=50 && marks <60 )||(marks==60))

The switch statement

Switch statement fulfils the same role as an if- statement and

everything that can be done with a switch can also be done with an

if-statement, but not the other way around. The structure of a

switch is shown in example 3.

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The conditional operator (also known as the ternary operator)

The conditional operator has the following structure:

(Test expression)? (Results if true): (Results if false)

Consider the following example:

String sResult = (marks>=50)? “Pass”: “Fail”;

As always, the right-hand side of an assignment must be evaluated

first

The conditional expression is evaluated first and if it is true, the

value “Pass” is assigned to sReport else the value “Fail” is assigned to

sReport.

According to the specified naming convention in Appendix A, each

variable is prefixed with the first letter of it type e.g. sReport is a

string type

Table below shows Logic operators for Boolean conditions

Operator Description

== Equal to

!= Not equal to

>= Greater than or equal to

<= Smaller than or equal to

&& AND

|| OR

^ XOR

! NOT

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I will not do all the previous papers , apart that from

being impossible ,this guide doesn’t focus on the quantity

of information but it focuses on the quality by giving you

best strategies to program and to find the fast and

effective algorithms of any java problem you will

encounter in the future.

LetStart(“With Xolani”);

if(result.LeftBehind()==true)

{

string promise = “ I will pick you up “;

this.GoTogetherAgain(I.promise);

}

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1. Consider the above screen print. Cisco is looking for the best junior programmer from the two universities: University of KwaZulu-Natal and University of the Free State. You are required to develop a software that will allow each applicant to register.

Instructions

The age of the student must be in this range: 18 – 21, display an error message if it beyond or less.

Ensure that the student only select one university

The date of birth must be in the form dd/mm/yyyy and use it to calculate the age

For User Profile button (btnUserProfile) display a name tag in the text Area. The name tag must be as follows

The button new user must clear all the fields including the text area

The button Generate Code, must append a three a character to the text area

a. Character 1 must be the first letter of the name (initial)

b. Character 2 must be any random number less than 10

c. Character 3 must be the last character of the surname

Surname Initial (age)

Gender

University

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Copyright©2015 X.S. Maphumulo

Example: Nicklaus Jobs, who was born in 1995 and studies at the University of the Free State.

Solution

It’s a good programming practice to instantiate variables or data fields at a higher level

(below the class name), that you will use in different scopes of the class. From the

question, you could see that there are some variables that we will use on both scopes

(button User profile and button Generate code) and those variables must be declared as

global variables of the class.

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//button – [User profile ]

private void btnUserProfileActionPerformed(java.awt.event.ActionEvent evt)

{

1. sName = txfName.getText();

2. sSurname = txfSurname.getText();

3. sDate = txfDateofBirth.getText();

4. String sGender = (String)cmbGender.getSelectedItem();

5. cInitial = sName.charAt(0);

6. String date = sDate.substring(6);

7. int Age =2015- Integer.parseInt(date);

8. String sNameTag = " ";

9. String university= " ";

10. if(Age>=18 && Age<=21)

11. {

12. if(radbtnUKZN.isSelected() && radbtnUFS.isSelected())

13. {

14. JOptionPane.showMessageDialog(null," Please select only 1 university");

15. }

16. else

17. {

18. if( radbtnUKZN.isSelected() )

19. {

20. university = "University of Kwa-Zulu Natal";

21. }

22. else if( radbtnUFS.isSelected() )

23. {

24. university= "University of the Free state";

25. }

26. else

27. {

28. JOptionPane.showMessageDialog(null," Select at least one university");

29. }

30. sNameTag+=sSurname +" "+cInitial+" ("+Age+")"+"\n"+sGender+"\n"+ university+"\n";

31. txtAreaOutput.setText(sNameTag.toUpperCase());

32. }

33. }

34. else

35. {

36. JOptionPane.showMessageDialog(null," Incorrect age");

37. }

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Explanation

Line 1-3 ,declare and assign the variables using the corresponding values from the

text fields

Line 4 , the selectedItem() method of a combobox , checks the selected item then

it returns it as an object that can either be a string , integer , a real

number(double) or a character. We therefore have to explicitly type cast the

object to string type: (String) cmbgender.getSelectedItem ().a numerical example

showing type casting

double dNumber=13.5;

int iNumber = (int) dNumber;

Now iNumber will be 13

Line 5, we use the charAt (int index) method to get the first letter of the name

which is assigned to cInitial .Note cInitial was declared at the top of the class.

Nicklaus

0123456

Therefore charAt (0) will return ‘N’ as a character.

Line 6, the method substring have two different signatures and that is called

method overloading. The first one uses two parameters and in this current

exercise we would have used it as follows:

String date=sDate. Substring (6, 4); where 6 is the begin index and 4 it length

Which means the compiler will start from character six to extract and take only 4

characters ahead the 6th one.

On the other hand, String = sDate.substring (6); tells the compiler to substring

starting from 6 to the rest of the word.

Line 7, In order to calculate the age, we must firstly convert the year of birth to an

integer then take 2015 minus the year converted.

Line 8-9,I have declared to variables : sNameTag (to display name tag ) and

university (to get the selected university from radio buttons)

Line 10, Validation : checks if the age is greater than 18 AND (&&) less than 21

Line 12,This is called a nested if-else statement(have an else-statement nested to

another) .Basically, we now check if the user selected the both of the radio buttons

if its true use dialog to display the error message if not continue to check .

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Line 17-28, we check which university is selected then overwrite the value of the

variable “university”, if the user did not select any of the two display an error

message on line 28.

Line 29, if all the conditions are true: the user selected only one university then we

concatenate the variables required for a name tag. NOTE the escape characters

are used just to format the name tag. “\n” – next line and “ \t” tab or spaces

Check in appendix A for all escape characters.

Line 31, we display sNametag which holds the name tag, we used the method

toUppercase () just to display sNametag in capital letters.

Line 36, Look at the code again you will note that we nested everything inside the

validation of the age. In line 34 the else-statement states that if the age is not

between 18-21 then display an error message in line 36.

//button – [New user]

private void btnNewUserActionPerformed(java.awt.event.ActionEvent evt) {

1. txfSurname.setText("");

2. txfName.setText("");

3. txfDateofBirth.setText("");

4. txtAreaOutput.setText("");

5. JOptionPane.showMessageDialog(null," You may input all your details");

Explanation

private void btnNewUserActionPerformed(java.awt.event.ActionEvent evt) {

Line 1-3, We clear the text fields by overwriting their text values to an empty string

Line 4, text areas and fields uses the same properties and methods hence the text

area in internet programming is called a multiline text field.

Line 5, display a dialog indicating that all text fields are cleared.

//button - [Exit]

private void btnExitActionPerformed(java.awt.event.ActionEvent evt) {

1. System.exit(0);

Exit the program, for enrichment: There is a class called System, it one of the

most powerful classes in java. You can use the intellisense to explore more of it

functions

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//button – [Generate code]

private void btnGeneratePinActionPerformed(java.awt.event.ActionEvent evt) {

1. char sLast = sSurname.charAt(sSurname.length()-1);

2. int number =(int)Math.random()*10;

3. String sPin = cInitial + String.valueOf(number) + sLast;

4. txtAreaOutput.append(sPin.toUpperCase());

Explanation

Line 1, We are required to take the last character of the surname to formulate

the code

Let’s visits arrays. Since arrays are zero-based (starts from zero) then every set

of length N the last term will be N-1.

X O L A N I

0 1 2 3 4 5

We could see that the actual length of the word”xolani” is 6 but according to

arrays its 5 then if we let the Length to be n the last element will be n-1

Line 2, we have a Math.random () method which is used to get a random

number, but this method returns a double so we must type cast it to an integer.

NOTE in order to determine the maximum number of the random number you

must multiply with it hence here we multiplied by 10 because we want the

random number from 0 -10.

Line 3-4, we construct the code. Note we used the method String.valueOf () to

convert the random number to a string type. If this conversion was left out, the

three characters would return a sum not the consented string

2. You are developing an electronic voucher validator for a software company. The

application must check if the voucher is valid then add the name of the customer

to the combo box. The user must be able to delete the customer by selecting the

name then delete it.

Instructions

Voucher is validated as follows

I. The length of the voucher must 5 characters

II. The first character must be an integer

III. The last four characters must be letters

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Ensure that you display a message showing that the user was

successfully deleted.

The button add must only add the user if the voucher is valid

Solution

//button Add private void btnAddActionPerformed(java.awt.event.ActionEvent evt) {

1. String sVoucher = txfVoucher.getText();

2. if(sVoucher.length()==5)

3. if(Character.isDigit(sVoucher.charAt(0)))

4. if(Character.isLetter(sVoucher.charAt(1)))

5. if((Character.isLowerCase(sVoucher.charAt(2)) &&

(Character.isLowerCase(sVoucher.charAt(3))&&Character.isLowerCase(sVoucher.charAt(4)))))

6. cmbCustomers.addItem(txfNameSurname.getText());

7. }

Explanation

In programming everything builds on top of each other, therefore I will not explain

some of things I did on the previous exercise. Fasten your seatbelts it's going to be

a bumpy ride.

Line 2, we check whether the length is equivalent to five characters if not the

execution does not continue until the length is five.

Line 3, Assuming that length was five, we now check whether the first character of

the voucher is a digit. The Character class uses a lot of static methods to validate

characters .The best way to know which method to use, just type Character

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followed by a dot the intelliSpaense will give you options and since they are self-

explanatory, it will be easy to pick the appropriate one.

Line 5, checks the last 3 characters whether they are letters or not.

Please know how to nest if-else statements and also know how to write

compound if-else statements.

Line 6, finally we now add the name to the combo box, the combo box uses a

method addItem (), which adds any object to the combo box.

//button – [Delete]

private void btnDeleteActionPerformed(java.awt.event.ActionEvent evt) {

1. if(JOptionPane.showConfirmDialog(null, "Are you sure?")== 0)

2. {

3. cmbCustomers.removeItem(cmbCustomers.getSelectedItem());

4. JOptionPane.showMessageDialog(null, " deleted");

5. }

6. else

7. {

8. JOptionPane.showMessageDialog(null, " You did not delete");}

Explanation

Deleting, clearing, disposing and closing are damaging operations so before we

execute them, we need to confirm from the user.

Line 1, we confirm from the user, using the confirm dialog.

The dialog consist of three buttons, if the user clicks a yes it returns a zero

Hence my if-else statement checks if it zero then delete the name and surname.

If the user clicks no from the confirm dialog, line 8 will be executed.

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3. Consider the screen print above, you are responsible for electronic investments

that are made by clients to your Bank. Develop a software that will allow a user to

make an investment. You will output a report showing the results of the simple

interest and compound interest, accumulated amounts. You have to append the

user’s details below the two amounts.

Your report must be as follows:

Use the following formulas to calculate for investments amount

1) A = P (1+i x n) – Simple interest

2) A = P (1+I )2 - Compound interest

Accumulated amount in Simple interest : <amount>

Accumulated amount in Compound interest : <amount>

Date of birth : < date of birth>

Surname and Initial : <surname initial>

Gender: <gender>

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Instructions to follow

The label “display percentage” must constantly display the percentage when the

use slides the knob of the slider.

Use the ID number to output date of birth e.g. 26 March 1998

Hint

The first 6 digits indicate the date of birth in this form YYMMDD

Use the ID number to output the gender ,

Hint

The four digits in position 7 to 10 of an identity number (ID number) indicate a

person's gender. The following applies:

>=5000: Male

< 5000: Female

Calculate and display both simple and compound interest amounts using the same

data.

Use a Dialog to output your report and must be capitalize.

Example: Emily Swift with an ID 9803260431083 and input the following data for

the investment

Amount to Invest: 12000

Years: 2

Interest: 20%

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The following screen print shows the output of the above entered data.

Solution

//button –[ Report]

private void btnReportActionPerformed(java.awt.event.ActionEvent evt) {

1. double dAmountInvest = Double.parseDouble(txfAmountInvested.getText());

2. int iYears =(int) SpinnerYears.getValue();

3. double dPercentage = (SliderInterest.getValue()*1.0)/100;

4. String sNameSurname = txfNameSurname.getText();

5. String ID = txfIDNumber.getText();

6. String sSurname =sNameSurname.substring(sNameSurname.indexOf(' ')+1);

7. char cInitial = sNameSurname.charAt(0);

8. String sGender=" ";

9. int iGender = Integer.parseInt(ID.substring(6,10));

10. if(iGender>=500)

11. {

12. sGender= "Male";

13. }

14. else

15. {

16. sGender = "Female";

17. }

18. String sDateOfBirth = " ";

19. if(ID.length()==13)

20. {

21. String idn = ID.substring(0,6);

22. String day = idn.substring(4,6);

23. String year = "19"+ idn.substring(0,2);

24. int month = Integer.parseInt(idn.substring(2,4));

25. String sMonth= " ";

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26. switch( month)

{

case 1: sMonth += "January";break;

case 2: sMonth += "February";break;

case 3: sMonth += "March";break;

case 4: sMonth += "April";break;

case 5: sMonth += "May";break;

case 6: sMonth += "June";break;

case 7: sMonth += "July";break;

case 8: sMonth += "August";break;

case 9: sMonth += "September";break;

case 10: sMonth += "October";break;

case 11: sMonth += "November";break;

default:sMonth += "December ";break;

27. }

28. sDateOfBirth = day + " "+ sMonth+ " "+ year;

29. }

30. double dAmountInSimple= Math.round( dAmountInvest*( 1+ dPercentage*iYears ) );

31. double dAmountCompound = dAmountInvest * Math.pow(1 + dPercentage, iYears);

32. double dAmountCompoundInvest = Math.round(dAmountCompound);

33. String sOutput= " ";

34. sOutput += "Simple Interest : "+dAmountInSimple+ "\n Compound Interest :

"+dAmountCompoundInvest+"\n";

35. sOutput += "Date of birth : "+sDateOfBirth+ " \nClient : "+ sSurname+ " "+cInitial + " \n";

36. sOutput+= "Gender : "+sGender;

37. JOptionPane.showMessageDialog(null,sOutput.toUpperCase());

Explanation

Line 1, instantiates the variable for the amount to be invested.

Line 2, creates a new variable year that will hold the value of the spinner.

The getValue () method of a jSpinner returns an object so we must type cast (int)

the object to an integer.

Line 3, interest can be a double or an integer but I used a double because a double

type can hold an int value but an integer (int) cannot hold a value with a decimal

(double).

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SliderInterest.getValue()*1.0;

The above code is extracted from line 3. I multiplied by 1.0 to make the whole

expression a double, so that I will be able to divide by 100 then get the actual

percentage. For instance, the user may slide the knob and select 20 then to get the

actual percentage you will have to divide 20 by 100 then get 0.2 of which is a double.

If the factor 1.0 was omitted a logic error would occur because an integer divide by

an integer returns an integer.

Example

double y =10/9;

The value of y is 1.0

But

double y = (10 * 1.0)/9;

The value for y is 1.111112

Line 4, gets the name and the surname of the client. There must be a

single space between the name and the surname.

Line 5, gets the Id from the text fields as a string

Line 6, I substring or extract the surname from the “sNameSurname”

which contains both name and surname separated by a single space.

The indexOf() method get the first occurrence of the single space of

which occurs between the name and the surname. indexOf(‘ ‘)+1 simply

means move 1 step after finding a space then start to substring the rest

of the text of which is now a surname. Follow me here

Xolani Maphumulo

There is a single white space between the “i” and the “M”.The method

simply tells the compiler to add 1 after that single space and when we

add one we Jump to the M of the surname,then from ‘M’ we substring

or extract everything that follows M of which is “Maphumulo”.

Line 7, we use the same variable “sNameSurname” to get the first letter

of the name. Since we start by a name so charAt(0) will return the first

letter of the name.

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Line 8, A good programmer declare and assign a variable with an empty string if

he/she knows that the variable will need to be overwritten in different conditions.

I assigned sGender with an empty because if iGender is greater than 5000 then

sGender must be a Male else a female.

Line 10 – 17, we overwrite the value of sGender according to the value of iGender.

Line 19, checks whether the ID contains 13 characters.

Line 21, returns the first six characters of the date of birth from the ID.The

characters are in the form YYMMDD.

Line 22, extracts the day from idn.

Line 23, we get the year of birth. Note the question states that we must assume

that everyone was from 1900 and an ID only contains two characters of the year so

we will prefix “19” to the year of birth from the ID.

Line 25-27, since we are required to display the month in words, so I used switch

statement to determine which month at a certain case.

The if-else statement may also be used.

Line 28, Concatenate all variable required for the date of birth.

Line 30, calculate the accumulated amount for the simple interest. It is still

acceptable to have many variables for calculating the accumulated value, in fact it

very good compared to what I did.

Line 31, I want you to pay attention on the Math.pow() method since the number

of years must be an exponent so we must write it as the second parameter of the

method.

Line 33-36, the variable sOutput is used to display the report using a dialog.

Everything can be done in one line but I decided to keep on appending for the sake

of readability.

Line 37, display the report stored in sOutput.

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Copyright © 2015 X.S Maphumulo

//Slider -[ Interest ]

private void SliderInterestStateChanged(javax.swing.event.ChangeEvent evt) {

1. lblSlider.setText(String.valueOf(SliderInterest.getValue()));

Explanation

Line 1, In order to constantly display the changing value of the slider, the stateChanged() event handler of the slide will keep track of every value the knob changes to.

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By reading the whole question surely you have noticed that we must have a global variable “kilometres” that will be available to all the scopes of the class. The below screen capture shows the instantiation of this global variable.

//button – [Delivery] Question 1.1

private void btnDeliveryActionPerformed(java.awt.event.ActionEvent evt) {

1. String departure = (String) (cmbDepart.getSelectedItem());

2. String destination = (String) (cmbDestination.getSelectedItem());

3. kilometres = Integer.parseInt(txfDistance.getText());

4. lblDelivery.setText(departure + " to " + destination + " : " + kilometres + "km");

}

Explanation

Line 1, we get the departure from the combo box as a string. Since the

getSelectedItem() method of the combo box returns an object we had to type

cast the object to a string.

Line 2, get the destination as the selected item from the combo box.

Line 3, overwrites the value of kilometres by the value the distance text field.

Line 4, display using the label, Ensure that your output is the same as that of the

screen capture provided. The setText() method is found in any component

,basically it overwrites the value of the text of the component ,to the text

specified as a parameter.

Button – [Delivery Cost] Question 1.2

private void btnDeliveryCostActionPerformed(java.awt.event.ActionEvent evt) {{

5. int position = (int) (lstKgs.getSelectedIndex()); 6. double costTransport = 0; 7. switch (position) 8. { 9. case 0: costTransport = 0.6 * kilometres; break; 10. case 1: costTransport = 1.0 * kilometres; break;

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11. case 2: costTransport = 1.25 * kilometres; break; 12. case 3: costTransport = 1.65 * kilometres; break; 13. } 14. if (chbSpeedPost.isSelected()) 15. { 16. costTransport += 100; 17. } 18. txfCost.setText(String.format("R%2.2f",costTransport));

}

Explanation Line 5, The list class contains a method getSelectedIndex() which returns the

index of the selected item. According to the screen the selected item is 1 since in programming we start counting from 0.

Line 6,instantiates the variable that will hold the transport cost line 7 – 13, calculates the value of the transport cost .The selected index is used

to check for different cases .if the user selects the first category , position in line 5 will hold 0 then the transport cost will be calculated according to the case 0.

Line 14 – 17, checks whether “chckSpeed” is selected or not. If its selected R100 will be added to the transport cost.

Line 18, displays the transport cost to the text field. If you take a close look in the parameter of the setText() method, you will see that we didn’t only display but we also formatted the value to 2 decimal places.

Button – [Delivery box Number] Question 1.3

private void btnBoxNumberActionPerformed(java.awt.event.ActionEvent evt) {

1. int boxNumber = 0;

2. if (chbSpeedPost.isSelected())

3. {

4. boxNumber = 4;

5. }

6. else

7. { //opening the else statement

8. do

9. {

10. boxNumber = (int) (Math.random() * 5) + 1;

11. } //closing do-while

12. while (boxNumber == 4);

13. } //closing the else statement

14. txfBoxNumber.setText("" + boxNumber);

}

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Explanation

I have commented the braces to not get you confused.

Line 2, checks whether the check box is selected, if yes then overwrites the value of boxNumber to 4.

Line 6-12, the Boolean statement simply means IF chbSpeedPost (checkbox) is not selected then do the following. So long as boxNumber is 4 the statement will return a true then continue to acquire a random number until boxNumber is not 4, that’s where the statement will return false then the compiler will stop executing line 8.

Line 14,displays boxNumber to the text field

Button - [Validate bar code] Question 1.4 private void btnBarCodeActionPerformed(java.awt.event.ActionEvent evt) {

1. String sbarCode = txfBarCode.getText(); 2. int sumOdd = 0; 3. int sumEven = 0; 4. for (int n = 0; n < sbarCode.length()-1; n ++) 5. { 6. if ((n+1) % 2 ==0) 7. { 8. sumEven = sumEven + Integer.parseInt(sbarCode.substring(n, n + 1)); 9. } 10. else 11. { 12. sumOdd = sumOdd + Integer.parseInt(sbarCode.substring(n, n + 1)); 13. } 14. int sum = sumOdd * 3 + sumEven; 15. int checkDigit = 10 - (sum % 10); 16. if(checkDigit == Integer.parseInt(sbarCode.substring(sbarCode.length()-1))) 17. { 18. txfDisplayBarCode.setText("The bar code is valid. Check digit: " + checkDigit); 19. } 20. else 21. { 22. txfDisplayBarCode.setText("NOT valid. Correct check digit: " + checkDigit); 23. }

}

Explanation

Line 1, gets the bar code from the text field and store it to a variable “sbarCode”

Likely we are given the algorithm to follow when answering this question. Read until you understand what is expected from you to write.

Line 2-3, creates two new variables and give them a value of zero.

Line 4, a for-loop stepping through each character of the bar code stored in sbarCode.

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Line 6, checks all numbers in the bar code that are in the logical even position. Consider the following bar code 4373494603233 All the red numbers are in the logical even position while the blacks one are odd.

Line 8, we add all the numbers in logical even positions. Line 8 may also be written as follows sumEven += Integer.parseInt(sbarCode.substring(n, n + 1));

Line 10, all the numbers that are in logical odd positions are now added in line 12.

Line 14,According to the algorithm, before we get the total sum we must first multiply the sum of odds by 3

Line 15, as per instruction of the algorithm, to get the check digit we must: 10 – (sum modulus 10) which means we subtract the sum modulus 10 from 10. Modulus means the remainder after division.

Line 16 – 23, verifies if the checkdigit is equivalent to the last digit of the bar code ,if that is true then the bar code is valid else it’s not valid.

Button - [view and save deliveries] Question 1.5

I gave the background information about text files on section C so bear with me and browse section C before you try to answer this question. private void btnViewDeliveriesActionPerformed(java.awt.event.ActionEvent evt)

1. { 2. String place = (String)(cmbCityName.getSelectedItem()); 3. outputArea.setText(place+"\n"); 4. Try

5. { 6. PrintWriter out = new PrintWriter(new FileWriter( "December2014"+place+".txt"));

7. for (int i = 0;i<arrDecDeliveries.length;i++)

8. { 9. if(arrDecDeliveries[i].indexOf(place) >=0) 10. { 11. outputArea.append(arrDecDeliveries[i]+"\n”); 12. out.println(arrDecDeliveries[i]); 13. } 14. } 15. out.close(); 16. } 17. catch (IOException e) 18. {

19. JOptionPane.showMessageDialog(null,"Error");

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Explanation

Line 2-3, gets the place using the getSelectedItem() method of the combo box then Line 3 we display the place. The escape character “\n” is to prepare the next line for the next output.

Line 4 -16, the use of try –catch statement is to avoid run-time errors as we now dealing with external files. Line 6, we write to a file using the PrintWriter class which takes the name of the file as a parameter.

Line 7, the one dimensional array “arrDecDeliveries” contains a date and the name of the two cities.

Line 9, checks whether the place written exists, if it exists in the array “arrDecDeliveries” the indexof() method will return a number greater than 0.

Line 12 -15,writes the value of text to the file then close the file

If there is a problem with the external file the dialog message will be displayed.

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SECTION B


Object Oriented Programming (OOP)

Develop a class, including data fields and methods

Write parameterized methods that return a value

Develop different constructors

To apply programming techniques such as loops

Defensive programming.

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Introduction

Classes

Class is a template that contains similar objects. The object is referred to as the instance

of the class not the class itself. All along we’ve been using classes that are found inside

the library (JCL) to solve problems called predefined classes. In this section we will

develop and implement our own classes, user-defined classes.

Methods

In object oriented programming in order to use any member of a class we follow a

certain hierarchy.

For instance, let’s consider a scenario where I want to format a decimal value to two

decimal places using DecimalFormat class.

Package/namespace: import java.text.DecimalFormat;

Object instantiation: DecimalFormat f = new DecimalFormat("0.00");

method : System.out.println(f.format(16.5666));

In order to access the method format we must have a package then a class and method.

Method signature- is composed of the access modifier, return type, method name and

parameters

public int getSum(int iNum1,int iNum2)

The above method shows a method signature

Access modifier – is public which means you can access the method from other

classes .If the method is private it’s not accessible to external classes. We declare

data fields and methods as private if we want to enforce business rules or

validation.

The return type- the above method returns an integer and to indicate which type

is returned by the method ,you must include that type in the signature.Methods

that returns a value are called accessor methods

and methods that does not return a value are called mutator methods.Mutator

methods are mostly used for displaying and to pass parameters.

The method name, is the most significant part of the method signature. A class

may have more than one method with the same name as long as the signature is

different.

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Example:

We have an - Substring(int beginValue) which takes one parameter

We also have – Substring(int begin ,int end) which takes two parameters

They both sit on the same class inside JCL. The signature is different because they

have different number of parameters. A signature may differ by a single letter.

This is called method overloading

Parameters are used to pass value from one class to another or one method to

another. The order of parameters must be the same in the method call and in the

method signature.

The static and non-static keywords

The keyword static plays a huge role to a programmer

Once the method is declared with a keyword static, a programmer does not have to

instantiate the object of a class in order to use that method.

Non-static methods

Non static methods are called instances. A programmer must instantiate the object in

order to use the method.

Main Method

This is the most crucial method in any programming language. Everything that is written

to any class must be called inside the main method in order for it to be executed. The

following code shows the main method signature

public static void main(String[]args)

Access modifier – public so that everyone may access it.

Static – It’s a static method, hence you don’t have to instantiate any object before

you call the main method

void – The return type indicate it doesn’t return a value but output everything

inside it

main- it just a name for the method

String[]args - it passes a string array as an argument or parameter

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Constructor

A Constructor is a special method that assigns initial values to the

object(initializes the object)

There are two types of constructors

1. Default Constructor- this type contains no parameters and it may be

empty inside the body or may give initial values to the global members

of the class

2. Parameterized Constructor – this type contains parameters and it

assigns members of the class to those parameters

Advanced Object Oriented programming

Inheritance

Inheritance – A technique used to form new classes, using existing classes as super or

base class of the new formed classes. The new classes are now called subclasses and

they inherits all the members of the super or base class, such as object, methods, data

fields and properties.

Advantages

Makes implementing new classes quick

Fewer errors

Programming becomes easier and understandable

A Flow chart showing the principle of inheritance

Super Class

Sub-classes

Vehicle

Car Truck

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The unified Modelling Language (UML) provides a graphical tools that can be used

to describe a system

Encapsulation – refers to the packaging of data fields and behaviors into a

single unit (class) so that implementation details are hidden and access is

restricted.

Polymorphism – refers to the ability of the objects belonging to different classes

respond to a method, field, or property calls of the same time.

Abstraction – refers to the mechanism through which details can be reduced and

factored out so that one can focus on a few concepts at a time. 1. You are an IT educator to a school situated in Durban called Zwelibanzi. You were

asked to develop an e-Report for a subject that will be used by learners in a remote

location. Your software must allow a learner to choose the term and specify the subject

she/he wants to check results for.

Questions

1.1 Write a class called CReport and code it as follows

1.1.1 Declare the following data fields as private

sNameSurname – name and surname (String)

sSubject - subject to view result for(String)

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sTerm – the term ( String)

dPaper1- the marks for paper 1 (double)

dPaper2-marks for paper 2 (double)

1.1.2 Write a default constructor and set to zero dPaper1 and dPaper2

1.1.3 Write a parameterized constructor to assign all data fields to their

Parameters. Each data field must have a parameter that is initialized to.

1.1.4 Write accessor methods for sNameSurname ,sSubject and sTerm.

1.1.5 Write a method called FinalMark() to calculate the final mark the method

must take the sum of the two marks(dPaper1 and dPaper2) then divided by

200. The method must return the rounded percentage of the two marks

1.1.6 Write a method Display() that will return a string as follows

If the returned percentage from FinalMark() is greater than zero but

less than 30 the method must return Fail

If the returned percentage from FinalMark() is greater than 30 but less

than 100 the method must return Pass

If the returned percentage from FinalMark() is greater than 80 but less

than 100 the method must return Pass with distinction

1.1.7 Write a method toString() that will return a concanated string .Copy and paste

the code below as it is.

return getTerm()+" "+getSubject()+" Report for "+ getNameSurname()+"\n"

+"The Final Mark is :"+ FinalMark()+"\n"+Display();

NB: there will be no code to copy and paste in the final exam

So it’s highly recommended that you understand this code

1.2 Go to form as show in the above screen capture, Under the button Report –

[bntReport]

1.2.1 Write a code to get that data from all text fields and the combo box

1.2.2 Create an object of CReport and pass all the parameters

1.2.3 Output the method toString() in a dialog box

Solution public class CReport { //Question 1,1

//Question 1.1.1

private String sNameSurname;

private String sSubject;

private String sTerm;

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private double dPaper1;

private double dPaper2;

//Question 1.1.2

public CReport()

{

dPaper1= 0;

dPaper2=0;

}

//Question 1.1.3 public CReport(String sNameSurname,String sSubject,String sTerm,double dPaper1,double dPaper2)

{

this.sNameSurname=sNameSurname;

this.sSubject=sSubject;

this.sTerm =sTerm;

this.dPaper1=dPaper1;

this.dPaper2=dPaper2;

}

//Question 1.1.4

public String getNameSurname()

{

return sNameSurname;

}

public String getSubject()

{

return sSubject;

}

public String getTerm()

{

return sTerm;

}

//Question 1.1.5

public double FinalMark()

{

double dFinal = (dPaper1+dPaper2)*1.00/200;

double dFinalPerc = Math.round(dFinal *100);

return dFinalPerc;

}

//Question 1.1.6

public String Display()

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{

String sDisplay = " ";

double dMark = FinalMark();

if(dMark>=0 && dMark <=30)

{

return sDisplay += "You Failed";

}

else if( dMark >=30 && dMark<=100)

{

return sDisplay += "You Passed";

}

else if(dMark>= 80 && dMark<=100)

{

return sDisplay +="Passed with a distinction";

}

else

{

return sDisplay +="Invalid Mark";

}

}

//Question 1.1.7

public String toString()

{

return getTerm()+" "+getSubject()+" Report for "+ getNameSurname()+"\n"

+"The Final Mark is :"+ FinalMark()+"\n"+Display();

}

}

//Question 1.2

Button- Reports [btnReports]

2. String sTerm = (String)cmbTerm.getSelectedItem();

3. String sNameSurname = txfNameandSurname.getText();

4. String sSubject = txfSubject.getText();

5. double dPaper1= Double.parseDouble(txfPaper1.getText());

6. double dPaper2= Double.parseDouble(txfPaper2.getText());

7. CReport report = new CReport(sNameSurname, sSubject, sTerm, dPaper1,

dPaper2);

8. JOptionPane.showMessageDialog(null,report.toString());

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Explanation

Question 1.1.1

We declare the required data fields or members. Data fields must always be

declared as private unless stated otherwise. We ensure that we declare

them as high as we can so that they will be available to every scope hence

they are also termed global members of the classs

Question 1.1.2

It a good programming practice to always write a default constructor where

you give initial values to data members ,eventually they will be overwritten.

Question 1.1.3

Parameterized constructor (constructor with parameters) we created a

parameter for each data member and if you notice the names are exactly

the same. To not confuse the compiler since we have used the same names

we introduced the this-reference

The this-reference act as an arrow that tells the compiler that this member

of class is equivalent to this parameter

Public class Example {

private String sName;

public Example(String sName)

{

this.sName = sName;

}

If you find this confusing, you are allowed to not use the same

names for parameters and data members but also ensure the

order of parameters is the same.

Question 1.1.4

An accessor method is a method that returns a value. These methods will

help every time when we need the value of the returned variable.

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Question 1.1.5

We instantiated a variable called dFinal, to calculate the weighted average

of the two papers.I multiplied by the factor 1.00 to change the expression

to a double type, from there I can now divide by 200.

Since we must return a percentage, I multiplied the value of dFinal by 100 ,

we now have the percentage .The Math.round() method is used to format

the percentage to 2 decimal places. We finally return dFinalperc with the

value of the formatted percentage.

Question 1.1.6

In an if-else statement each condition affects the value that will be

returned by the method, so in this question it wise to return a value of each

condition. We take the value returned in FinalMark() method by just calling

the method and assign it to a new local variable with the same data type,

double Mark. It was also possible to just use the method itself without

creating a new variable but for the readability sake let’s stick on this

approach

Question 1.1.7

Master the principle of concatenation in java, you will never struggle to

write the body of the toString() method. Try to understand how I

concatenated each variable to another. The methods getTerm() ,

getSubject() and getNameSurname they just hold the value for

sTerm,sSubject and sNameSurname respectively.

Question 1.2 button Report

We get the term from the combo box using the method getSelectedItem()

that returns an object then we explicitly convert it to a string.

Gets the two papers

We instantiate the object of the CReport in order to connect with all the

members of the class.

CReport report = new CReport(parameters in their order)

We take all the variables instantiated in this form and pass them to the

CReport class.

We need to display the method toString() that holds a report which sits

inside the CReport class. JoptionPane as our dialog box then

report.toString() means in the CReport class take the toString() method .

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SECTION C


Problem Solving

To Read , Write and Manipulate an external text file

To apply advanced string manipulation

Use complex operations to arrays

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External text files

Until now all the programs we wrote, data is saved in the random static

memory hence we always have to enter it from scratch each and every time

when we run the program. JCL provides classes that can be used to

permanently store data that we execute on our programs, then later we just

read the stored data. The class PrintWriter and BufferedReader can be used

to store data in a text file and also read the data later.

The basic code to write to a text file

PrintWriter writer = new PrintWriter(new FileWriter(“filename.txt”);

writer.println(“Type what you want to save to a text file”);

writer.close()

The basic code to read from a text file

BufferedReader br = new BufferedReader(new FileReader(“filename.txt”);

String sLine = br.readLine();

System.out.println(sLine+ “\n”);

Br.close();

Using a Scanner class to read from a text file

File text = new File(“filename.txt”);

Scanner scnr = new Scanner(“filename.txt”);

while(scnr.hasNextLine()){

String line = scnr.nextLine();

System.out.println(line +”\n”);

}

Arrays – A data structure that may contain variables of the same type.

Before you enter the exam room you should know to do the following:

Declare and Instantiate an array

Sort , Sum,average,median,highest,lowest and length

You should know how to remove Duplicates

Display a 2-dimensional array into a matrix

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Defensive programming

Since we working with external files error handling is the crucial aspects

of this section

First technique is the try-catch statement

try

{

Body of the whole program

}

catch()

{

Display the message if there was an error

}

This statement is very useful when reading a textfile basically, it tells

the compiler to TRY and execute the source code then CATCH any run-

time error that it may encounter.

If-else statement also plays a huge role in defensive programming and

validation

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The File Class

The file class provides us with the static methods for the creation, deletion,

moving and opening files.

File file = new File(filename);

To check if a file exist

If(file.exists())

{

Code if the file exists

}

else

{

File does not exist

}

Deleting a files

If(file.exists())

{

f.delete();

}

Move/Rename

if(file.exists()) {

file.renameTo(new File(NEW_FILENAME)); }

Before any operation you must first verify whether the file

exist else you will run into a run-time error

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Text manipulation

Let consider a case where we want to manipulate data from a text file.The

data is delimited by a certain character. For instance, a whitespace or tab.

Example below shows how a text file is manipulated using the method split()

Example: You run a book store and you store all your book’s information in a

text file called “Book.txt” each line of data in the text file is structured as

follows

Code Book description Cost of the book

The screen print shows the first 4 lines of Book.txt

Code that reads a Book.txt object

1. BufferedReader in = new BufferedReader( new FileReader("Books.txt")); 2. String line = in.readLine(); 3. String[] sbook = line.split("\t"); 4. String code = sbook[0]; 5. String description = sbook[1]; 6. String price = sbook[2]; 7. System.out.printf("%-12d%-12d%07d\n","Code","description","price"); 8. System.out.printf("%-12d%-12d%07d","======","========","========""); 9. System.out.printf("%-12d%-12d%07d\n",code,description,price); 10. in.close();

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Output

Code Descripiton Cost

==== ========= =====

Book Java-with-xoh R123.0

e-Book Nighted R200

Book Perl R140

Explanation Line 1,The bufferedReader class was instantiated to get the external file Book.txt

Line 2,sLine takes each line of the text file

Line 3, sLine is broken down into columns delimited (separated) by a tab.

then each column is temporarily saved to the new array sbook.

A tab was used as delimiter in this question however there are several delimiters.

The following ones are mostly used therefore you should know them

o \w - Matches any word character.

o \W - Matches any nonword character.

o \s - Matches any white-space character.

o \S - Matches anything but white-space characters.

o \d - Matches any digit.

o \D - Matches anything except digits.

Line 4 -6, The text file contains 3 columns: Code, Description and Cost

and they will be transferred to sbook[0],sbook[1] and sboo[2] accordingly.

sBook[0] = Code

sBook[1] = Descciption Each column is saved in a new column

sBook[2] = Cost

Line 7-9, This display the heading : Code Description Cost

Line 8 , Underline the heading

Line 9 , append each column under it heading

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Solution

The fragile and non-fragile item must be instantiated as global variables

// Button – [btnLoad Load item] 3.1

private void btnLoadActionPerformed(java.awt.event.ActionEvent evt) {

1. String loadingCode = "";

2. if (rbtFragile.isSelected())

3. { if (fragileItems.length() < 20)

4. {

5. loadingCode = "F" + (fragileItems.length() + 1);

6. fragileItems += "*";

7. }

8. } else

9. {

10. if (nonFragileItems.length() < 30)

11. {

12. loadingCode = "NF" + (nonFragileItems.length() + 1);

13. nonFragileItems += "*"; }

14. } txfLoadingCode.setText(loadingCode);

15. if (loadingCode.equals(""))

16. {

17. JOptionPane.showMessageDialog(null, "Loading of item cannot be processed - No loading

space\n", "Information", WIDTH);

18. }

19. txaOutput.setText("Loading progress display area: \n================\n\n");

20. txaOutput.append(String.format("%-20s%-25s%n", "Fragile items:", fragileItems));

21. txaOutput.append(String.format("%-20s%-25s", "Non-fragile items:",

nonFragileItems));

Explanation

In line 1 , the variable that will hold the loading code was instantiated.

Line 2, we verify whether the radio button for fragile items was selected or not.

The method is isSelected() returns true or a false

Line 3, we secondly check if the length is less than 20 (for maximum fragile

items),if that is true then In Line 5 we overwrite the value of loadingCode

according to the instructions. F is for fragile items then the length will determine

how many asterisks

For instance if a user types F5 to the loading code text field

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The output will 5 asterisks which implies that the following line of

States that the number after ‘F’ is the length of the fragile items

And the asterisks will be displayed equally to the length

Line 6, if the length is less than 20 we will constantly concatenate an asterisk to

fragileItems ( global variable)

Line 8, we assume that if the radio button for fragile items is not selected, radio

button for non-selected item will be selected. Then we do the same process we

check if the loadingCode contains the length that is less than 30

The loadingCode is composed as follows

NFLength or NLength , length is a numerical value that will determined by the

number of asterisks that must be displayed

Line 14-15, once we get the loadingCode, we can then display it to the text area.

Line 15 , checks whether the loadingcode is null or it an empty string if it is we

then output an error message using a dialog

Line 19-21, the values of fragile items and non-fragile items is formatted then

displayed to the text area.

//Button – [btnCheckload Check load status] Question 3.2

private void btnStatusActionPerformed(java.awt.event.ActionEvent evt) {

1. int numFragile = fragileItems.length

2. int numNonFragile = nonFragileItems.length();

3. double percFragile = (numFragile) / 20.0 * 100;

4. double percNonFragile = (numNonFragile) / 30.0 * 100;

5. txaOutput.setText(" Load status report:\n=====================\n");

txaOutput.append(String.format("%-15s%-25s%-15s%n", " Item type" "Number of items",

"Percentage loaded"));

6. txaOutput.append(String.format("%-15s%-25s%-13.2f%n", " Fragile", numFragile, percFragile));

7. txaOutput.append(String.format("%-15s%-25s%-13.2f%n", " Non-fragile",

numNonFragile, percNonFragile));

8. if (percFragile >= 50 && percNonFragile >= 50)

9. {

10. txaOutput.append("\n The delivery may progress.");

11. }

12. if (numFragile < 10 || numNonFragile < 15)

13. {

14. txaOutput.append("\n The delivery may not progress.");

15. if (numFragile < 10)

16. {

17. txaOutput.append("\n Number of fragile items still required : " + (10 - numFragile));

18. }

19. if (numNonFragile < 15)

20. {

21. txaOutput.append("\n Number of non-fragile items still required : " + (15 - numNonFragile));

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22. }

23. }

24. }

Explanation

Line 1-2,gets the length of the of fragile and non-fragile items

Line 3-4, The maximum number of fragile items must be 20

then we calculate the percentage of the fragile items.

The non-fragile have a maximum of 30 so compute the quotient then get the

percentage.

Line 5-7, For readability the heading is underlined then in Line 6-7 we display the

percentages of the fragile and non-fragile items

Line 8,We use a compound if-else statement to check if both of the computed

percentages are greater than 50 .The dialog message only indicates that they are

greater than 50 . Do not confuse the following two:

&& - logic AND used when both condition must be true.

|| - logic OR used when one of the two conditions must be true.

Line 14, if both of the percentages are not greater or equivalent to 50 then we

output a dialog message, informing the user that he/she may not continue with

the delivery

Line 15-17 , Remember the maximum number for fragile items is 20 then in order

to have 50% of fragile items so that a user may continue with the delivery, he/she

must actually have a length of 10 fragile items:

10 20 0.5 100 = 50% From the equation above then we can conclude that the user who didn’t get 50%

actual got less than 10. We verify if the user have less than 10 then inform the

user using the dialog box, the number that is required in order to have 50% then

continue with the delivery.

Line 18, the same thing in line 15-17 but in this case the maximum number for

non-fragile items is 30 then in order to get 50% the user must actually have 15

non-fragile items. We verify if the user have less than 15 then use a dialog to

inform the user the number of required non-fragile items in order to continue

with the delivery

10 30 0.5 100 = 50%

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//Button – [btnClear Clear load] Question 3.3

private void btnClearActionPerformed(java.awt.event.ActionEvent evt) {

1. fragileItems="";

2. nonFragileItems="";

3. txaOutput.setText("");

Explanation

Line 1-3 , overwrites the values of fragile and non-fragile items to an empty string

.Line 3 clear the text field

1. Consider the screen print below. Develop an algebraic calculator that will allow a

user to enter the values for a, b and c (quadratic) or m and c (linear) then use

those values to solve for x-intercept and y-intercept. Display both intercepts in

the dialog box.

Instruction

The user must select only one equation to solve

If selected both, display an error message.

Use a dialog to output the intercepts

𝑥 =−𝑏±√𝑏2−4𝑎𝑐

2𝑎 Use it to solve for the x-intercept

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2. As a challenge re do exercise 1 but now allow the user to select both

radio buttons and output both solution in Dialog, The solution must not

be a number only but it must show steps, show factors before you

arrive at the final answer.

3. Write a concise description in two text files, the descriptions are about

programming (“programming.txt”) and artificial intelligence

(intelligence.txt) .Allow a user to select from the combo box which

description to read and then also write a code to read that specified

text file in the Button Display Description.

Example: If a user select Programming

“You might not think that that programmers are artists,

but programming is an extremely creative profession .It’s

Logic-based creativity”

~John Romero

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4. Using the above screen capture. Develop an application with which you and your

friend can exchange secret messages .The button – Encode and save must encode

the content of the text area by changing it to a reversed form, the content of the

text area then save it to a text file. The button read and decode must first decode

the content from the reversed state to the original state (readable) then display it

to the text area.

Example: if a user types “Xolani” then it must saved as “inaloX” to a text file.

To read it must be changed from “inalox” to “Xolani”.

5. Using Exercise 3 above, Develop the same application but this time use classes

and methods to add functionalities.

Write a class called “CMessage” with the following methods

A mutator method Save () that will encode the content and save it.

A mutator method Read () that will read and display the content.

It a problem solving so there are no restrictions you can use methods with

parameters and other strategies so long as the two mentioned methods are

found inside the class.

NOTE: You must connect the class with the graphical user interface.

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Solution to Exercise 1

private void btnSolutionActionPerformed(java.awt.event.ActionEvent evt) {

1. double m = Double.parseDouble(txfLinearM.getText());

2. double c = Double.parseDouble(txfLinearC.getText());

3. double xLinear = (-1*c*1.00)*m;

4. double yLinear = c;

5. double a= Double.parseDouble(txfQuadraticA.getText());

6. double b= Double.parseDouble(txfQudraticB.getText());

7. double C= Double.parseDouble(txfQuadraticC.getText());

8. double xQuad1 = ((-1*b ) + Math.sqrt(Math.pow(b,b) - (4*a*C)))/2.0*a;

9. double xQuad2 = ((-1*b ) - Math.sqrt(Math.pow(b,b) - (4*a*C)))/2.0*a;

10. double yQuad = C;

11. String sLinear = "The solution for Linear equation :\n x="+xLinear +" and y="+ yLinear ;

12. String sQuadratic = " The solution for the quadratic equation :\n"

13. +"x=" + xQuad1 +" or x ="+xQuad2 +", y="+yQuad;

14. if(radbtnLinear.isSelected() && radbtnQuadratic.isSelected())

15. {

16. JOptionPane.showMessageDialog(null,"Select only one equation");

17. }

18. else

19. {

20. if(radbtnLinear.isSelected())

21. {

22. JOptionPane.showMessageDialog(null,sLinear);

23. }

24. else if( radbtnQuadratic.isSelected())

25. {

26. JOptionPane.showMessageDialog(null,sQuadratic);

27. }

28. else

29. {

30. JOptionPane.showMessageDialog(null,"Please select at least one radio button");

31. }

32. }

Solutions for exercise 2, 3 and 4 will be posted on the ftp server or you can email me will

forward them to your email account.

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356 | P a g e


This appendix specifies the following

Explains the naming conventions and how to give names to Variables, classes and controls.

It summarizes methods and classes that found in the JCL (library)

Contains links for useful resources and sites

Provides the history of java and Why the author chose java

357 | P a g e


The purpose of naming conventions is to facilitate easier maintenance of code. This is

accomplished by naming all entities in a java program such that

It can be distinguished from other entities

Its function is evident

Its class type can be identified

If we stick to jTextbox1, jTextbox2, jButton1 etc. as controls were named by Netbeans,

we will soon run into trouble to comprehend the purpose of controls or variables, to

follow the logic of a piece of code and to maintain the code.

The following table shows how controls are named however some of the controls are

not mentioned here.

Prefix Description Example

Txf /txt Text field txfName

lbl label lblDisplay

btn button btnReport

radbtn Radio button radbtnLinear

cmb Combobox cmbGender

frm form frmHome

timer tmr tmrCount()

Variables

Variables of the primitive type are prefixed as follows

float - f

int , int32 - i

double - d

boolean - is/her

char - c

String – s

358 | P a g e


Loops counters and variables for capacity are not necessarily prefixed. It is convention

use i, j, k (for loop counters) and n or m for observations or array lengths.

Arrays

Arrays are prefixed with “arr” for instance arrNames means an array of names. The

programmer may write the full word without the prefix arr since arrays are collections.

Classes

In this guide I used a convention called Pascal case where a class is prefixed with the

capital letter C.

Description of the escape sequence

Escape Sequence Description

\b backspace

\t Tab

\n Next line

\f Form feed

\r Carriage return

\” “ Double quotation mark

\’ Single quotation mark

\\ backslash

Access to methods

Access modifier Description

public Any class can use this method

private Use by the class only –protected data

Protected Method(member) accessible in a class ,

other class in the same package and

subclasses outside the package

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Bibliography Blignaut ,P.J (2014) , Be sharp with C#

Havenga M & Moraal C .(2007), Creative java programming part 2

Approach

java with xoh for exams

Documents