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

Variables: associatie (1)

Variables: associatie (2)

Objects: instance variables instance methods

Voorbeeld Object: letter ‘a’

Classes en Objects

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

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

Variables: overzicht kenmerklocal variable / parameter instance variableclass variable plaats van declaratie vòòr gebruik ergens binnen method, constructor of block; in method-declaratie ergens binnen class, maar buiten methods; bij voorkeur private ergens binnen class, maar buiten methods; static en bij voorkeur final gebruik waarde slechts van belang voor method, constructor of block waarde van belang voor object’s state en meerdere methods meestal gebruikt voor constanten zichtbaarheid onzichtbaar buiten method, constructor of block zichtbaar voor alle methods in de class; onzichtbaar voor andere classes zichtbaar voor alle methods in de class; ook zichtbaar buiten de class, als public levensduur start – exit uitvoer van method, constructor of block object-aanmaak met new – verdwijnen van referentie naar object start – exit uitvoer programma

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

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()

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)

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

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); }

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;

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

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; }

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)) }

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

Class var./method: gebruik in class public class public static void main (String [] args) { } }

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

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

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; }

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."); } }

Graphics

Graphics class of AWT package

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

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

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(); }

Vormen tekenen

Gele achtergrondvorm stoplicht // 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 kleur van de vorm

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);

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);

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

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(); }