Program Realisation 2 Todays Topics Pixels, coordinates, and - - PowerPoint PPT Presentation

Program Realisation 2 http://www.win.tue.nl/˜hemerik/2IP20/ Lecture 9 Kees Hemerik Tom Verhoeff Technische Universiteit Eindhoven Faculteit Wiskunde en Informatica Software Engineering & Technology Feedback to T.Verhoeff@TUE.NL

c 2006, T. Verhoeff @ TUE.NL 1 Program Realization 2: Lecture 9

Today’s Topics

• Pixels, coordinates, and rectangles in Delphi
• Event mechanism in Delphi
• Memory leaks, dangling references
• UML: Unified Modeling Language
• (Automated unit testing)
• Conclusion

c 2006, T. Verhoeff @ TUE.NL 2 Program Realization 2: Lecture 9

Pixels and coordinates

x=0 1 2 3 y=0 1 2 y=0 1 2 3 x=0 1 2 3 4

• Pixels are not points, but little squares
• Coordinate options:

through pixel centers , between pixels

• For many purposes, coordinates between pixels are preferred

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Rectangles

• FillRect(XL, YL, XH, YH) colors the points x, y such that

XL ≤ x < XH ∧ YL ≤ y < YH

• It has width XH - XL and height YH - YL
• FillRect(X0, YL, X1, YH) and FillRect(X1, YL, X2, YH) are horizon-

tally adjacent: they touch, but do not overlap

• FillRect(X, YL, X, YH) is empty
• Scales well: FillRect(0, 0, XH, YH) vs. FillRect(0, 0, 2*XH, 2*YH)
• Edsger W. Dijkstra. Why numbering should start at zero. EWD 831,
• Aug. 1982

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Framed Rectangles

y=0 1 2 3 x=0 1 2 3 4 4 5 6 7

• Rectangle(0, 0, 5, 4) ; Rectangle(4, 0, 7, 4)
• These share a 1-pixel boundary, or each has 0.5-pixel boundary
• In final assignment, we want Rectangle(0.5, 0.5, 4.5, 3.5) and

Rectangle(4.5, 0.5, 6.5, 3.5)

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Event Mechanism in Delphi: Main Event Loop

1 program PrDirTreeView; 2 3 uses 4

Forms,

5

Main in ’Main.pas’ {Form1};

6 7 begin 8

Application.Initialize;

9

Application.CreateForm(TForm1, Form1);

10

Application.Run;

11 end.

Application.Run starts the main event loop

The main event loop waits for an event and calls its event handler

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Event Mechanism in Delphi: Event

• Events are triggered by user actions and object state changes
• Events are implemented as private fields with method pointers,

e.g. of type TNotifyEvent

• TNotifyEvent = procedure (Sender: TObject) of object;
• Procedure types
• Cannot be accommodated in the static call graph

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Memory Leaks and Dangling References Memory leak : after p := q or New(p) or p := ...Create(...) , (old p)ˆ is possibly still allocated but unreachable

• The amount of usable memory has diminished (leaked away)
• GetHeapStatus reports some memory statistics (e.g. TotalAllocated)

Dangling references : after

Dispose(p) or p.Free , other references

could still point to (old p)ˆ

• References to disposed/freed objects are called ‘dangling’
• The objects pointed to are no longer valid and are unreliable

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Memory Leaks and Dangling References: Examples See final assignment, Main.pas:

1 // invariants --------------------------------------------------------- 2

...

3 // I2: (FFocus = nil) or (FFocus is a node in the tree with root FRoot) 4

...

5 procedure TForm1.ChangeRoot(APath: String); 6 begin 7

FFocus := nil;

8

FRoot.Free;

9

FRoot := MakeDirTree(APath);

10 end;

Omitting FRoot.Free causes a memory leak after line 9 Omitting FFocus := nil, makes FFocus a dangling reference after line 8 (violating I2)

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UML: Unified Modeling Language

• Standard graphical language for modeling object-oriented software
• Syntax: Diagrams, but also textual representation (OCL)
• Semantics: somewhat controversial
• For (static) structure and (dynamic) behavior
• Extensible, still evolving
• Not a design method

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Automated Unit Testing Framework

• For each unit U, write a separate unit test driver Test_U
• Test_U uses U, makes various calls of U, and checks the results
• DUnit for Delphi, or FPCUnit for FreePascal/Lazarus
• XUnit test framework provides classes for organizing test cases,

and checking and reporting of results

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Main Theme: Modular Structure

• Manage Complexity
• Separation of Concerns
• Divide and Conquer
• Design by Contract

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Why Modular Structure?

• Correct construction

Manage complexity

• Team construction

Reduce development time

• Verification

Errors are inevitable

• Adaptation

Change is inevitable

• Reuse

Reduce budget

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How to Design During design, many decisions must be made Design guidelines, principles, and methods needed Modular structure: how to ‘find’ the modules

• Top-down design , stepwise refinement, functional decomposition
• Bottom-up design

Functionality versus data as basis for modularity

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Main Themes

• Abstract Data Types and object-oriented programming
• Recursion , both in control and in data
• Event-driven, interactive Graphical User Interfaces
• Borland Delphi with Object Pascal

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What Next?

• 2IA20: Ontwerp van Algoritmen 2
• 2IF10: Componenten 1

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