Transcript A simple software developement process from specification

The non-trivial Java example
‘Mouse in a Maze’
A simple software development process
from specification, to design,
implementation, and test
DAAD project
“Joint Course on OOP using Java”
Humboldt University Berlin, University of Novi Sad, ‘Polytehnica’ University of Timisoara,
University of Plovdiv, University of Belgrade
Author: Klaus Bothe
Version: Sep. 29, 2004
Source
Based on an idea from S.N.
Kamin, M.D. Mickunas, E.M.
Reingold: „An introduction to
computer science – Using
Java“, McGraw-Hill, 1998
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2
Points of this Java sample
program
Introduce a
non- trivial
Java program
Illustrate a
methodology how
to present larger
Java programs in
lectures
Using Java API
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For
the lecturer
only
Demonstrate the
importance of
software
engineering
principles for
ordinary Java
program
development
Interactive style of
the lecture
improves learning
effects
3
Course materials
For
the lecturer
only
 Lecture slides:
• about 90 slides
• takes 3 x 2 lecture hours at HU (interactive style)
 Java sources
Classes
LOC
Mouse
61
Maze
55
MouseMaze
64
Easel
23
SoftFrame
135
MazeTest
40
Sum:
378
 Assignments:
• modify, extend the program
• implement as an applet (grafical interface)
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Didactical mistake in presenting complex
Java programs in lectures
For
the lecturer
only
 The lecturer tries to explain each technical detail of
program code
 non-understandable in a lecture
 boring
 The lecturer starts with a Java program too early
 details of requirements specification still open
 design / class structure not well discussed
Finding a proper class structure may be more challenging
then implementing the Java program code.
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Didactical principles in presenting
complex Java programs in lectures
For
the lecturer
only
 Follow the software engineering process:
• requirements analysis, design, implementation & test
 Involve students into this process (interactivity)
 Only outline the main ideas of the implementation
 Assignments support detailed understanding the
code
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Requirements analysis:
‚Mouse in a Maze‘
Task:
Develop a program, that simulates the
movement of a mouse in a maze (labyrinth)
from an entry to an exit.
What to do?
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Next steps?
7
Facts concerning software
development phases
Most errors of software systems result from
misunderstanding the problem to be solved.
Software development consists only of a
small part of programming:
•
•
•
•
Requirements analysis: 20 %
Design:
15 %
Implementation: 20 %
Test: 45 %
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Learning goals
This example should illustrate the
importance of a complete and correct
requirements specification for the project
success.
Before implementing, the next step is the
design of the application: Which
components belong to the program
architecture?
Starting with the implementation too early
may lead to project’s failure.
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Development process of
‚Mouse in a Maze‘
Requirements analysis
Design
Implementation and test
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Requirements analysis:
‚Mouse in a Maze‘
Task:
Develop a program, that simulates the
movement of a mouse in a maze (labyrinth)
from an entry to an exit.
Open questions ?
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Open questions
How does a maze look like?
What is a mouse able to do (e.g. which
kinds of movements)?
What is the initial state of the mouse?
What, if there is no way from entry to exit?
In which way should the solution be
presented?
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How does a maze look like?
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Examples of our kind of mazes
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Requirements specification (1)
Develop a program, that simulates the movement of a
mouse in a maze (labyrinth) from an entry to an exit.
1. The Maze
A maze is a collection of quadratic rooms arranged in a
rectangle. Two adjacent rooms are separated by a wall or
opening (gap). The maze is surrounded by a wall which is
open at two locations (entry and exit). The size of the
maze (length and height) is variable.
Examples:
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How does a mouse look like?
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Our mouse
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Mouse confronted with different
mazes
No
problem

This will
become hard 
exit
entry
exit
entry
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Which kinds of movements is our
mouse able to do?
step forward
turn left
turn right
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Possible movements of the mouse
May move one step
forward into the
adjacent room in the
line of vision
exit
entry
May turn left or right
by 90 degrees
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Two implemented solutions
exit
entry
entry
 Proper solution for the
wrong problem.
 In each case: the shortest
path has been found.
What may be
suspicious with these
solutions?
exit
 Requirements specification is
incomplete
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Requirements specification is
incomplete
entry
exit
entry
exit
 In each case: the shortest path has been found
 Only possible if the mouse knows the whole maze (view
from above)
 This is not the characteristic of maze problems.
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Perceptions of the mouse
Line of vision only
straight forward
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exit
entry
May decide: Am I inside or
outside the maze?
May see only inside of one
room (not into the adjacent
room)
May decide: Do I
face a wall or an
opening (gap)?
23
Field of view of a mouse
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The problem may be huge 
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Requirements Specification (2)
2. The Mouse:
The mouse has no general overview of the maze.
a) The mouse may move in the following way:
turn left, turn right (by 90 degrees), move forward
into the adjacent room.
b) The mouse is located either in a fixed room inside the
maze or just next to the entry or exit. In addition, it
has a fixed line of vision.
c) The mouse can see only in the line of vision. It can
decide wether it faces a wall or not.
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Requirements specification:
open problems?
Description of the initial state of the mouse
Description of the final state of the mouse
Description of the task
Special cases
User interface
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Requirements Specification (3)
3. Desription of the initial state of the mouse:
The mouse is initially placed in front of the entrance to
the maze (the next step forward takes her to the maze).
Example:
exit
entry
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Requirements Specification (4)
4. Desription of the final state of the mouse and of
the task:
We a looking for a sequence of movements (turn left,
turn right, step forward) leading the mouse from the
entry to the exit.
Example:
exit
entry
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Requirements Specification (5)
5. Special case:
If there is no exit or if there is no way from the entry to
the exit, then the mouse should leave the maze
through the entry.
Example:
entry
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Requirements Specification (6)
6. User interface
a) Textual output of the solution:
Example:
step forward, turn right, …
b) Graphical user interface:
The sequence of movements will be displayed with
the help of a graphical applet, i.e. the steps of the
mouse are visualized. The user can interactively
trigger the next step.
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Solvability of the problem
Is there an algorithm at all that
solves the problem for arbitrary
mazes taking into account the
characteristic properties of the
mouse?
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Algorithm: basic principle
Principle:
Have the mouse walk with its right side on
the wall of the maze.
Still not an algorithm
An algorithm has to determine the
sequence of mouse movements.
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Algorithm:
as a pseudo code program
only one step:
if mouse is still inside the maze:
turn right;
if (facing a wall?):
then
turn left and test if (facing a wall?);
if (facing a wall?) then turn left and test ...
else
step forward
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Strong pseudo code:
one step
IF (NOT outside the maze?)
BEGIN /*do next step*/
turn right;
WHILE (facing a wall?) DO
turn left;
ENDWHILE
step forward;
END
Impossible:
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Strong pseudo code:
whole algorithm
step forward; /* enter the maze */
WHILE(NOT outside the maze?)
BEGIN /*do next step*/
turn right;
WHILE (facing a wall?) DO
turn left;
ENDWHILE
step forward;
END
ENDWHILE
Think about: The algorithm fulfills the principle.
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Mouse movements according to the
algorithm: first example
exit
entry
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Mouse movements according to the
algorithm in detail: first example
exit
entry
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Mouse movements according to the
algorithm: second example
exit
entry
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Mouse movements according to the
algorithm in detail: second example
exit
entry
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Mouse movements:
graphical and textual output
exit
entry
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step
turn
step
turn
turn
turn
step
turn
turn
turn
step
turn
step
forward
right
forward
right
left
left
forward
right
left
left
forward
right
forward
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Textual output of the solution
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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xxxxxxxxxxxxxx
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xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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step forward
turn to the right
step forward
turn to the right
turn to the left
turn to the left
turn to the left
step forward
…
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Mouse in a maze – only a nice game?
Sample of finding algorithms for robots
dealing with different tasks:
• Playing soccer
• Robot moving on the moon
• Rescue robots
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Development process of
‚Mouse in a Maze‘
Requirements analysis
Design
Implementation and test
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Task
Requirements specification
Next step ?
Start with programming?
If so,
• with which part/component?
• ???
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Design: develop the software architecture
SW architecture description languages:
UML
Our task: define an object-oriented
architecture
Main problem: How to find classes?
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Software development:
Phases and results
Analysis & Definition
 Requirements specification
Design
 Software architecture
Implementation
 Program
Test
Test cases
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As a matter of fact …
Finding a proper class structure may
be more challenging then
implementing the Java program code.
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Software architecture
Structure of the software:
Which components exist?
Which relations are between them?
Stack:
Push(e)
Pop()
Top()
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Architecture specification languages
 Graphical languages for the specification of
software architectures
 Industry standard: UML
Unified Modelling Language
 Now: examples of one graphical element of UML:
class diagram
What programming languages mean to the
implementation phase, are architecture
specification languages to the design phase.
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UML classes: the structure
Name
Time
Attributes:
state
- hour : int
- minute : int
hidden
Time (hour: int, minute : int)
addMinutes (Min : int)
printTime ( )
Operations:
behaviour
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UML classes as interfaces
Time
- hour : int
- minute : int
UML classes provide
an interface: Which
information is visible
from outside ?
Time (hour: int, minute : int)
addMinutes (Min : int)
printTime ( )
Why are hidden data – which are
not visible from outside – part of
UML class?
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The usable interface of a class:
only visible features
Time
- hour : int
- minute : int
Time (hour: int, minute : int)
addMinutes (Min : int)
printTime ( )
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Hidden data support the
understanding of the
interface. They are part of
the class model.
The only way to
interact with objects
of this class is to call
its methods
53
Relations between classes:
Associations, inheritance, …
Class 1
Class 2
Association
Class 1
Class 2
Directed association: objects of
class one know objects of class
two – and not vice versa
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How to find classes?
Principles ?
By separation of the problem to subproblems
• Sub-problems may become classes
From the objects of the problem area
• Investigate the requirements specification to
find objects of the problem area
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Case study:
‘Mouse in a Maze’
Which objects of the problem area should be
implemented as component / class of the
system?
Mouse
Algorithm for
mouse movement
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Maze
User
interface /output
56
Which relations exist between the
components?
Which
relations ?
Mouse
Algorithm for
mouse movement
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Who needs
whom ?
Maze
User
interface /output
57
Which relation: Who needs whom?
no
Mouse
e.g. test if in
front of a wall
Maze
?
Alg. has not to know the maze
Algorithm for
mouse movement
User
interface /output
?
?
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Class diagram for a mouse
Which data and which operations
characterize the mouse?
Mouse
?
?
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Interface of the mouse:
Which data, which operations?
(first approach)
Mouse
State: place /
direction in a
maze
- Location : Point
- Direction : int
stepForward ( )
turnLeft ( )
turnRight ( )
facingWall ( ) : boolean
outsideMaze ( ) : boolean
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Behaviour:
abilities of the
mouse
(movements &
perceptions)
60
Detailed interface of the mouse
Mouse
+
Visible
attribute
Location : Point
Direction : int
started : boolean
theMaze : Maze
Mouse (Maze m)
getLocation ( ) : Point
stepForward ( )
turnLeft ( )
turnRight ( )
facingWall ( ) : boolean
outsideMaze ( ) : boolean
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Create a mouse in
relation to a
particular maze
Current position of
the mouse
61
Interface of the maze
Class diagram of the maze:
data and operations?
Maze
?
?
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Interface of the maze:
Which information is
necessary for a user of
this class (user = objects
of class “Mouse”)?
62
Interface of the maze
(first approach)
Maze
Is the current
position outside of
the maze?
outside (pos : Point) : boolean
checkWall (direction : int, pos :
Point) : boolean
getStartLocation ( ) : Point
Is there a wall at
position pos in this
direction?
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Where to place the mouse
initially? (position & direction)
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Interface of the maze: attributes ?
Maze
outside (pos : Point) : boolean
checkWall (direction : int, pos :
Point) : boolean
getStartLocation ( ) : ?
The representation of the maze is too complex to
be included as attributes (array)
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Detailed interface of the maze
Maze
- height : int
- width : int
Detailed maze data are too complex to
be included in a class diagram.
The height and width of the maze are
useful to draw the maze
getStartLocation ( ) : Point
getStartDirection ( ) : int
Height and width as a point.
getSize ( ) : Point
checkWall (direction : int, pos : Point) : boolean
checkWall (direction : int, col : int, row : int) : boolean
outside (pos : Point) : boolean
To find class diagrams is an iterative process: start with a
simple solution and extend and modify if necessary.
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Software Architecture:
the whole view (textual output)
Mouse
+
-
Location : Point
Direction : int
started : boolean
theMaze : Maze
Mouse (Maze m)
getLocation ( ) : Point
stepForward ( )
turnLeft ( )
turnRight ( )
facingWall ( ) : boolean
outsideMaze ( ) : boolean
Maze
-
height : int
width : int
getStartLocation ( ) : Point
getStartDirection ( ) : int
getSize ( ) : Point
checkWall (direction : int, pos : Point) : boolean
checkWall (direction : int, col : int, row : int) : boolean
outside (pos : Point) : boolean
Algorithm for
mouse movement
Textual output of the maze
main ( )
printMaze ( )
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Problems of the development of a
software architecture
Software architecture:
• Not unique (many good and many bad solutions)
Design of a software architecture does not
succeed for the first time
Long process:
• Software architecture develops stepwise
Principle:
• Start with one preliminary architecture
• The usability of the methods finally turns out only
during the implementation.
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Development process of
‚Mouse in a Maze‘
Requirements analysis
Design
Implementation and test
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Java sources
Classes
LOC
Mouse
61
Maze
55
MouseMaze
64
Easel
23
SoftFrame
135
MazeTest
40
Sum:
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378
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Information to the audience
This presentation gives only an outline of
the principle points of the implementation.
Several crucial technical details will be
explained.
However, not each implementation detail
will be presented. This would be boring in a
lecture.
During the self-study and with
assignments, everybody should explain
oneself open questions.
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Planning of implementation steps
In which order should the
classes be implemented?
2
Mouse
Algorithm for
3b mouse movement
Maze
1
User interface:
3a
Textual output of the
maze
 UML class diagram:
• Dependencies  order of implementation
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Software Architecture:
the whole view
2
1
Mouse
+
-
Location : Point
Direction : int
started : boolean
theMaze : Maze
Mouse (Maze m)
getLocation ( ) : Point
stepForward ( )
turnLeft ( )
turnRight ( )
facingWall ( ) : boolean
outsideMaze ( ) : boolean
Maze
-
height : int
width : int
getStartLocation ( ) : Point
getStartDirection ( ) : int
getSize ( ) : Point
checkWall (direction : int, pos : Point) : boolean
checkWall (direction : int, col : int, row : int) : boolean
outside (pos : Point) : boolean
3a
3b
Algorithm for
mouse movement
Textual output of the maze
main ( )
printMaze ( )
In the lecture: 1, 2, 3b (main ideas)
Self-study: 3a; 1, 2, 3b (details)
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Implementation of the maze
 Starting from the class diagram
Maze
- height : int
- width : int
getStartLocation ( ) : Point
getStartDirection ( ) : int
getSize ( ) : Point
checkWall (direction : int, pos : Point) : boolean
checkWall (direction : int, col : int, row : int) : boolean
outside (pos : Point) : boolean
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Representation of the maze as
a data structure
How to represent the maze
by Java data structures?
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Position in a maze
 Position = coordinate (x,y)
= (number of column, number of line)
(0,0)
(1,0)
(2,0)
(3,0)
(4,0)
(5,0)
(0,1)
(1,1)
(2,1)
(3,1)
(4,1)
(5,1)
(0,2)
(1,2)
(2,2)
(3,2)
(4,2)
(5,2)
(0,3)
(1,3)
(2,3)
(3,3)
(4,3)
(5,3)
(0,4)
(1,4)
(2,4)
(3,4)
(4,4)
(5,4)
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Movement path of the mouse
Path: (0,2), (1,2), (1,3), (1,2), (1,1), …, (4,0)
(0,0)
(1,0)
(2,0)
(3,0)
(4,0)
(5,0)
(0,1)
(1,1)
(2,1)
(3,1)
(4,1)
(5,1)
(0,2)
(1,2)
(2,2)
(3,2)
(4,2)
(5,2)
(0,3)
(1,3)
(2,3)
(3,3)
(4,3)
(5,3)
(0,4)
(1,4)
(2,4)
(3,4)
(4,4)
(5,4)
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Movement path of the mouse:
Long form
Detailed description:
(0,2), step forward to (1,2), turn to right, step forward to (1,3), turn
to right, turn to left, turn to left, turn to left, step forward …
(0,0)
(1,0)
(2,0)
(3,0)
(4,0)
(5,0)
(0,1)
(1,1)
(2,1)
(3,1)
(4,1)
(5,1)
(0,2)
(1,2)
(2,2)
(3,2)
(4,2)
(5,2)
(0,3)
(1,3)
(2,3)
(3,3)
(4,3)
(5,3)
(0,4)
(1,4)
(2,4)
(3,4)
(4,4)
(5,4)
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Representation of the maze:
store the walls
For each relevant position:
• Is there a wall to the south
 boolean [][] sWall
• Is there a wall to the east
 boolean [][] eWall
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Representation of the maze:
store the walls
boolean [][] sWall
(0,0)
(1,0)
(2,0)
(3,0)
(4,0)
(5,0)
(0,1)
(1,1)
(2,1)
(3,1)
(4,1)
(5,1)
(0,2)
(1,2)
(2,2)
(3,2)
(4,2)
(5,2)
(0,3)
(1,3)
(2,3)
(3,3)
(4,3)
(5,3)
(0,4)
(1,4)
(2,4)
(3,4)
(4,4)
(5,4)
boolean [][] eWall
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South walls of the maze: example
boolean [][] sWall =
{{true, true, true, false},
{false, false, false, true},
{false, false, false, false},
{true, true, true, true}}
(0,0)
(1,0)
(2,0)
(3,0)
(4,0)
(5,0)
(0,1)
(1,1)
(2,1)
(3,1)
(4,1)
(5,1)
(0,2)
(1,2)
(2,2)
(3,2)
(4,2)
(5,2)
(0,3)
(1,3)
(2,3)
(3,3)
(4,3)
(5,3)
(0,4)
(1,4)
(2,4)
(3,4)
(4,4)
(5,4)
DAAD project „Joint Course on OOP using Java“ ©
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South walls of the maze: the array
boolean [][] sWall =
{{true, true, true, false},
{false, false, false, true},
{false, false, false, false},
{true, true, true, true}}
0
1
2
3
0
true
true
true
false
1
false
false
false
true
2
false
false
false
false
3
true
true
true
true
DAAD project „Joint Course on OOP using Java“ ©
81
Method ‘outside’
public boolean outside (Point pos){
return ((pos.x < 1)
//left ...
||
(pos.x > width)
//right ...
||
(pos.y < 1)
//over ...
||
(pos.y > height)
//under ...
);
// the maze
}
API:
Point pos
DAAD project „Joint Course on OOP using Java“ ©
: (x , y)
82
Method ‘checkWall’: technical detail
Boolean checkWall
(int dir, int col, int row)
{
switch (dir){
case NORTH: return
sWall[row-1][col-1];
case SOUTH: return
sWall[row][col-1];
...
(0,0)
(1,0)
(2,0)
(3,0)
(4,0)
(5,0)
(0,1)
(1,1)
(2,1)
(3,1)
(4,1)
(5,1)
(0,2)
(1,2)
(2,2)
(3,2)
(4,2)
(5,2)
(0,3)
(1,3)
(2,3)
(3,3)
(4,3)
(5,3)
(0,4)
(1,4)
(2,4)
(3,4)
(4,4)
(5,4)
DAAD project „Joint Course on OOP using Java“ ©
83
Components:
separate implementation & separate test
Component test:
• Test of the component independent of the rest
of the system.
Integration test:
• Later on, the collaboration with other
components will be tested.
DAAD project „Joint Course on OOP using Java“ ©
84
Component test of the maze
class Maze {…
}
Component
to be tested
class MazeTest {…
}
Testframe for
class Maze
DAAD project „Joint Course on OOP using Java“ ©
85
Test frame:
basic principles for test output
% java MazeTest
Start location is (0,2): [x=0,y=2]
Start direction is EAST = 1: 1
Outside true : true
Not outside -> false : false
Not outside -> false : false
Wall -> true : true
No wall -> true : true
Wall -> true : true
Actual value
Expected value
Semantic interpretation
DAAD project „Joint Course on OOP using Java“ ©
86
Implementation of the mouse
 Starting from the class diagram
Mouse
+
-
Location : Point
Direction : int
started : boolean
theMaze : Maze
Mouse (Maze m)
getLocation ( ) : Point
stepForward ( )
turnLeft ( )
turnRight ( )
facingWall ( ) : boolean
outsideMaze ( ) : boolean
DAAD project „Joint Course on OOP using Java“ ©
87
Communication between the objects:
send a message
Operation of the
mouse
public boolean facingWall() {
return
theMaze.checkWall (direction, location);
}
Operation of the
maze
DAAD project „Joint Course on OOP using Java“ ©
The mouse sends a
message to the maze: ‘If I
have a certain location and
direction in the maze, is
then a wall in front of me?’
88
Methods: ‘turnLeft’ and ‘turnRight’
public void turnLeft() {
printoutMove(“turn to the left”);
direction = (direction + 3) % 4;
}
public void turnRight() {
printoutMove(“turn to the right”);
direction = (direction + 1) % 4;
}
Think about these formulas.
DAAD project „Joint Course on OOP using Java“ ©
89
Method: ‘stepForward’
public void stepForward() {
switch (direction) {
case NORTH: location.y--;
case EAST:
location.x++;
case SOUTH: location.y++;
case WEST:
location.x--;
}
printoutMove(“step forward”);
}
DAAD project „Joint Course on OOP using Java“ ©
break;
break;
break;
break;
90
Search algorithm:
class ‘MouseMaze’ (1)
public static void main ( ... ) {
Maze theMaze = new Maze();
Mouse littleMouse = new Mouse(theMaze);
printMaze(theMaze);
Moves the
mouse one
step
forward, if
necessary
with turns
//move the mouse step by step
do{
makeStep(littleMouse);
}
while (!littleMouse.outsideMaze());
}
DAAD project „Joint Course on OOP using Java“ ©
91
Search algorithm:
class ‘MouseMaze’ (2)
private static void makestep(Mouse m){
if (m.started){
if (!m.outsideMaze()){
m.turnRight();
Visible
while (m.facingWall()){
attribute
m.turnLeft();
}
m.stepForward();
}
} else {
m.stepForward();
m.started = true;
}
}
DAAD project „Joint Course on OOP using Java“ ©
Moves the
mouse one
step
forward, if
necessary
with turns
92
Critics of the implementation
 Constant NORTH = 0, … repeatedly defined in three classes

source of error

better solution: define them in an interface only once
 Variable ‘started’ visible outside

instead of this:
- private + additional access operation
- modify the algorithm
 Data representation of the maze is error-prone
• true/false sequencies correct ?
• Variables height, width, size may be in contradiction to eWall, sWall
 better let them compute
 Strategy of the mouse may be a part of the mouse:
Other mice may have other strategies: move at the left-hand wall
(mice = plural of mouse)
DAAD project „Joint Course on OOP using Java“ ©
93