Algoritmiek

1. Algoritmiek Variables and Methods Graphics Hoorcollege 10 - Ma. 6 nov. 2006 L.M. Bosveld-de Smet

2. Variables: associatie (1)

3. Variables: associatie (2)

4. Objects: instance variablesinstance methods

5. Voorbeeld Object: letter ‘a’

6. Classes en Objects

7. Variables: kenmerken • Naam • Data Type • 8 primitive types • onbeperkt aantal object of reference types • Bereik (Scope) • Levensduur (Lifetime) • Initialisatie • Declaratie

8. Variables: verschillende soorten • Local variables • Parameters • Instance variables (non-static fields) • Class variables (static fields)

9. Variables: overzicht

10. public class variable: voorbeeld • Constante van de Math class (java API) public static final double PI = 3.1415926535…; public class PrintPI { public static void main (String[] args){ System.out.println(Math.PI); } }

11. Instance variable: voorbeeld public class Bicycle { … … … private int speed; … … … public Bicycle (int startSpeed) { speed = startSpeed; } … … … public int getSpeed (){ return speed; } … … … } instance variable constructor: Bicycle myBicycle = new Bicycle (10); getter method: myBicycle.getSpeed()

12. public class method: voorbeelden • Methods van de Math class (java API) public static int round (float a) public static double sqrt (double a) public static double random () Math.round(5.5)

13. private class variable / public class method: voorbeelden public class Bicycle { … … … private int speed; private int id; private static int numberOfBicycles = 0; … … … public Bicycle (int startSpeed) { speed = startSpeed; id = ++numberOfBicycles; } … … … public static int getNumberOFBicycles(){ return numberOfBicycles; } … … … } class variable class method: Bicycle.getNumberOfBicycles

14. local variables: voorbeeld (1) public class Adding { public static void main (String[] args) { int next=1; int total = 0; while (next > 0) { next = Integer.parseInt(SimpleIO.readLine()); total = total + next; } System. out.println("Total is : " + total); } }

15. local variables: voorbeeld (2) while (workToDo (table)) { for (int r = 0; r < table.length; r++) { for (int c = 0; c < table [0].length; c++) { if (table [r] [c] > 3) { stamps += 4; table [r] [c] -= 4;

16. parameter: voorbeeld public void setFee (double newFee) { fee = newFee; } parameter doc.setFee (150.00);

17. Array parameters public class WordLists { public static void main(String[] args) String[] wordList1 = {"aap", "hond", "varken", "luipaard", "bever"}; String[] wordList2 = {"hortensia", "roos", "lelie", "geranium", "magnolia"}; System.out.println ("Longest word list 1: " + wordList1[longestWord(wordList1)]); System.out.println ("Longest word list 2: " + wordList2[longestWord(wordList2)]); } private static int longestWord(String[] list) { int indexLongestWord = 0; for (int i = 1; i < list.length; i++) { if (list[i].length() > list[indexLongestWord].length()) { indexLongestWord = i; } } return indexLongestWord; } }

18. Instance methods public class Person { private String name; public Person () { name = "no name yet."; } public Person (String initialName) { name = initialName; } public void setName (String newName) { name = newName; } public String getName () { return name; } public void writeOutput () { System.out.println ("Name: " + name); } public boolean sameName (Person otherPerson) { return (this.name.equalsIgnoreCase (otherPerson.name)) } }

19. Class methods: examples public static void callByName (String name) { system.out.print (name); } private static int updateScore (int currentScore, int points) { return currentScore + points; }

20. Class var./method: gebruik in class public class <class_name> <declaratie class variable(s)> public static void main (String [] args) { <main body> } <declaratie class method(s)> }

21. “helpers” • Class methods als “helpers” • “cohesion” • “stepwise refinement” • “top-down decomposition”

22. Verdeling van taken • Quiz-programma: • Stel een vraag aan de gebruiker • Lees het antwoord van de gebruiker • Controleer of het antwoord correct is • Geef adequate feedback • Hou de score bij

23. Class “helper” methods private static String readAnswer (String question) { SimpleIO.prompt (question); String userInput = SimpleIO.readLine(); return userInput.trim().toLowerCase(); } private static boolean match (String userAnswer, String correctAnswer) { return (userAnswer.equals(correctAnswer)); } private static void giveFeedback (boolean ok, String hurrah, String sorry) { System.out.println (ok ? hurrah : sorry); } private static void updateScore (boolean ok) { if (ok) { score += 10; } }

24. Gebruik van “helpers” in main import jpb.*; public class Quiz { private static int score; public static void main(String[] args) { score = 0; String userAnswer = ""; boolean isCorrect = false; userAnswer = readAnswer ("Waarvan is bit de afkorting?\n") ; isCorrect = match (userAnswer, "binary digit") ; giveFeedback (isCorrect, "Goed geantwoord!", "Sorry. Verkeerd antwoord."); updateScore (isCorrect) ; userAnswer = readAnswer ("Hoeveel bytes komen overeen met 32 bits?\n") ; isCorrect = match (userAnswer, "4") ; giveFeedback (isCorrect, "Het gaat prima zo!", "Wat jammer nu!") ; updateScore (isCorrect) ; System.out.println ("Your total score is " + score + " points."); } <declaration helpers> }

25. Graphics

26. Graphics class of AWT package

27. DrawableFrame object en methoden import java.awt.*; import jpb.*; public class <class name> { public static void main (String[] args) { // create drawable frame DrawableFrame df = new DrawableFrame(<frame title>); df.show() / df.setVisible(true); df.setSize(<width>,<height>); // obtain graphics context Graphics g = df.getGraphicsContext(); //make drawing <Graphics methods applied to Graphics object>; // repaint frame df.repaint(); } }

28. DrawableFrame- en Graphics-objecten graphics context frame / window line

29. DrawLine class // draws a line inside a frame import java.awt.*; import jpb.*; public class DrawLine { public static void main (String[] args) { // create drawable frame DrawableFrame df = new DrawableFrame("Line"); df.setVisible(true); df.setSize(200,200); // obtain graphics context Graphics g = df.getGraphicsContext(); // draw line g.drawLine(50,50,150,150); // repaint frame df.repaint(); } }

30. Vormen tekenen

31. Gele achtergrondvorm stoplicht kleur van de vorm // Draw background of sign g.setColor(Color.yellow) int[] xBackground = {0, 100, 200, 100}; int[] yBackground = {100, 0, 100, 200}; g.fillPolygon(xBackground, yBackground, xBackground.length); X coordinaten van vorm Y coordinaten van vorm

32. 5 geneste vierkanten // Draw five nested polygons to form the stripe on the // outer border of the sign g.setColor(Color.black); int[] xPolygon1 = {5, 100, 195, 100}; int[] yPolygon1 = {100, 5, 100, 195}; g.drawPolygon(xPolygon1, yPolygon1, xPolygon1.length); int[] xPolygon2 = {6, 100, 194, 100}; int[] yPolygon2 = {100, 6, 100, 194}; g.drawPolygon(xPolygon2, yPolygon2, xPolygon2.length); int[] xPolygon3 = {7, 100, 193, 100}; int[] yPolygon3 = {100, 7, 100, 193}; g.drawPolygon(xPolygon3, yPolygon3, xPolygon3.length); int[] xPolygon4 = {8, 100, 192, 100}; int[] yPolygon4 = {100, 8, 100, 192}; g.drawPolygon(xPolygon4, yPolygon4, xPolygon4.length); int[] xPolygon5 = {9, 100, 191, 100}; int[] yPolygon5 = {100, 9, 100, 191}; g.drawPolygon(xPolygon5, yPolygon5, xPolygon5.length);

33. Tekenen van stoplicht // Draw a black rectangle (the traffic signal) g.fillRect(77, 35, 46, 130); // Draw red,yellow,and green circles (the traffic // lights) g.setColor(Color.red); g.fillOval(83, 43, 34, 34); g.setColor(Color.yellow); g.fillOval(83, 84, 34, 34); g.setColor(Color.green); g.fillOval(83, 125, 34, 34);

34. Tonen van tekst Monospaced, Bold, 30 SansSerif, Italic, 30 Serif, Plain, 40

35. Toon tekst: programma import java.awt.*; import jpb.*; public class DisplaySum { public static void main (String[] args) { // create drawable frame DrawableFrame df = new DrawableFrame("Wirth's RULE"); df.setVisible(true); df.setSize(350,200); // obtain graphics context Graphics g = df.getGraphicsContext(); // display text in red monospaced bold font g.setColor(Color.red); g.setFont(new Font("Monospaced", Font.BOLD, 30)); g.drawString("DATA STRUCTURES + ", 15, 50); // display text in green sansserif italic font font g.setColor(Color.green); g.setFont(new Font("SansSerif", Font.ITALIC, 30)); g.drawString("ALGORITHMS = ", 15, 100); // display text in blueserif plain font g.setColor(Color.blue); g.setFont(new Font("Serif", Font.PLAIN, 40)); g.drawString("PROGRAMS", 15, 150); // repaint frame df.repaint(); } }