1

Intro to Java

Week 12(Slides courtesy of Charatan & Kans, chapter 8)

2

Software Quality

Learning objectives

By end of this lecture you should be able to:

document your code so that it is easy to maintain; distinguish between compile-time errors and run-time

errors; test a program using the strategies of unit testing and

integration testing; generate test data using the strategies of black box

testing, white box testing and stress testing; document your test results professionally using a test

log; explain the meaning of a Java program throwing an

exception; format your output to improve the usability of your

programs.

3

Measuring quality

There are many desirable features of a piece of software.

We will concentrate on the following:

maintainability;reliability;robustness;usability.

4

Maintainability

The requirements of an application often change over time.

Maintaining a system refers to the need to update an existing system to reflect these changing requirements.

Code should be designed in such a way as to make these changes easier rather than harder.

5

Documentation

For a software system to be easy to maintain, the software design also needs to be clearly documented.

When developing object-oriented programs, this design documentation should include:

complete class diagrams;clear method definitions (parameter &return types, plus pseudocode when

appropriate).

6

Reliability

When attempting to run a program two kinds of errors could occur:

compile time errors; run-time errors.

7

Compiler errors

8

Testing

Testing can never show the absence of errors, only the presence of them.

The aim therefore of any testing strategy is to uncover these errors.

Two areas of testing:

validation (making sure you are building the

right product); verification (making sure you are building the

product right).

9

Verification

A Java application typically consists of many classes working together.

Testing for such errors will start with a process of

unit testing (testing individual classes)

followed by

integration testing (testing classes that make up an application together).

10

Unit testing

All applications require a class with a main method before they can be run.

Two possibilities

add a main method into the class you aretesting;

writing a separate class especially to contain the

main method. This new class then acts as the

driver for the original class.

11

Dummy classes

Testing the StudentList class requires the Student class to be available.

You can develop your own dummy class in place of the missing class.

// a dummy student class class Student {

// no code in class }

12

Adding dummy methods to dummy classes

public double findStudentAverage (int i){ return student[i-1].calculateAverageMark( );}

class Student // ammended dummy class{ // additional dummy method public double calculateAverageMark() { return 50.5; } }

13

Integration testing

When the individual classes in a program have been tested they can be integrated and tested together.

If compiler errors occur during integration then check the following:

14

All methods called should have an implementation in the receiving class

Student

Student (…)

getName( )

setName(…)

StudentList

x = student[i-].calculateAverageMark( )?

15

Names of method calls should match exactly names of methods in receiving class

Student

double calculateAverageMark( )

StudentList

x = student[i-1].CalculateAverageMark()

?

16

Parameter list of method call should match exactly parameter list of methods in the receiving class

StudentList

x = student[i-1].calculateAverageMark(2)

?

Student

double calculateAverageMark( )

17

The expected type of values returned from the method calls should match the return types of these methods in the receiving class.

Student

double calculateAverageMark( )

StudentList

int x; x = student[i-1].calculateAverageMark();

?

18

Black box testing

component to test

? inputs expected outputs

19

Testing the method getGrade

Student Grades

marks 70 and above grade 'A'

marks in the 60's grade 'B'

marks in the 50's grade 'C'

marks in the 40's grade 'D'

marks in the 30's grade 'E'

marks below 30 grade 'F'

20

Test data produced

grade 'A'

grade 'B'

grade 'C'

grade 'D'

grade 'E'

grade 'F'

"mark too low"

"mark too

high"

79, 64, 55, 46, 33, 25, -40, 120

21

Testing the boundaries

If the code still fails to produce the correct result often the error lies on the boundaries of such equivalent groups.

In this case the following boundary values should all be tested as well as the sample from each equivalent group identified earlier:

-1, 0, 1, 29, 30, 31,39, 40, 41,49, 50, 51,59, 60, 61, 69, 70, 71, 99, 100, 101

22

White box testing

component to test

inputs based on code

expected outputs

topMark = 70;

// more code here

while(!valid)

{

if (mark > topMark)

grade = 'A';

//more code here

else

valid = false;

}

23

The test log

TEST LOG

Purpose: To test the STUDENTLIST class

Run Number: 1 Date: 17th March 2000Action Expected Output Pass/ Fail Reason for failureAdd student ("Ade") message "student

entered"

set mark to 69 no message expected get grade 'B' Add student ("Madhu") message "student

entered"

set mark to 70 no message expected get grade 'A' Displays 'B' instead of 'A'.

Due to error in if statementother tests

24

Robustness

A program is said to crash when it terminates unexpectedly.

A robust program is one that doesn't crash even if it receives unexpected input values.

Generally, whenever a value is received to be processed, it should be checked before processing continues; if an unexpected value could cause the program to crash.

25

A program will crash if an illegal array index is used

PushToLimitSalesStaff

for (int i = 1; i<=3; i++){ System.out.println ("enter sales for employee "+ i); value = EasyIn.getInt(); cars4U.setFigure(i, value); }

SalesStaff

public void setFigure(int numberIn, int valueIn){ staff[numberIn-1] = valueIn; }

'i' set to 3 last time round the loop

an attempt will be made to access index 2

26

Dealing with the problem

public boolean setFigure(int numberIn, int valueIn){ if (numberIn <= staff.length) { staff[numberIn-1] = valueIn; return true; // method succesful } else { return false; // method unsuccessful }}

27

Adapting the driver program

for (int i = 1; i<=3; i++){ System.out.println ("enter sales for employee "+ i); value = EasyIn.getInt(); boolean ok = cars4U.setFigure(i, value); if (!ok) // unable to set figure succesfully { System.out.println ("ERROR:last figure not entered "); } }

28

Usability

The usability of a program refers to the ease with which users of your application can interact with your program.

A user-manual can help make your programs easier to follow.

29

Adding a "HELP" option

*** REACTOR SYSTEM ***

[1] Get current temperature[2] Increase temperature[3] HELP[4] Quit

enter choice [1,2,3,4]: _

30

Escape sequences

Special formatting characters, known as escape sequences, can be added into strings.

Some useful escape sequences

\t add a tab space

\n add a new line

\" add a double quote

\' add a single quote

\\ add a backslash

31

The DecimalFormat class

The DecimalFormat class can be used to format the display of decimal numbers.

This class resides in the java.text package

import java.text.*;

Once you have access to this class you can create DecimalFormat objects in your program.

32

Creating DecimalFormat objects

The DecimalFormat constructor has one parameter, the format string.

DecimalFormat df = new DecimalFormat( "000,000.000");

33

Using a DecimalFormat object

Use the format method of the DecimalFormat class to format a given number:

DecimalFormat df =new DecimalFormat( "000,000.000");

double someNumber = 12345.6789;

System.out.println("before\t" + someNumber);System.out.println("after\t"+ df.format(someNumber));

before 12345.6789after 012,345.679

34

Optional digits

Replacing a zero in a format string with a hash (#) would mean that the digit was optional, not compulsory.

DecimalFormat df = new DecimalFormat( "#00,000.000");

double someNumber = 12345.6789;

System.out.println("before\t" + someNumber);

System.out.println("after\t" + df.format(someNumber));

before 12345.6789after 12,345.679

35

Graphical user interfaces