Hogwarts School Of Computer Science
From Huben's Wiki
(Created page with "''GLENDOWER: I can call spirits from the vasty deep.<br> ''HOTSPUR: Why, so can I, or so can any man; But will they come when you do call for them?''<br> Henry IV, Shakespeare '...") |
|||
| Line 1: | Line 1: | ||
| + | [[Image:Welcome To Hogwarts.jpg]] | ||
| + | |||
''GLENDOWER: I can call spirits from the vasty deep.<br> | ''GLENDOWER: I can call spirits from the vasty deep.<br> | ||
''HOTSPUR: Why, so can I, or so can any man; But will they come when you do call for them?''<br> | ''HOTSPUR: Why, so can I, or so can any man; But will they come when you do call for them?''<br> | ||
Henry IV, Shakespeare | Henry IV, Shakespeare | ||
| − | + | ==Welcome to Hogwarts School Of Computer Science!== | |
Computers are types of perverse and hostile Demons: we command them as our servants and they perform only exactly what we commanded, even if it was not our intention. | Computers are types of perverse and hostile Demons: we command them as our servants and they perform only exactly what we commanded, even if it was not our intention. | ||
| − | Computer demons speak many inhuman languages: our goal will be to learn fluency in one of those languages: | + | Computer demons speak many inhuman languages: our goal will be to learn fluency in one of those languages: JAVA. |
* We will read and write lengthy incantations called programs in the arcane language JAVA, and understand how these demons and their servants can be bent to our will. | * We will read and write lengthy incantations called programs in the arcane language JAVA, and understand how these demons and their servants can be bent to our will. | ||
* We will study the weird processes of demonic computation: how to invoke smaller demons called objects and how to make them dance for us. | * We will study the weird processes of demonic computation: how to invoke smaller demons called objects and how to make them dance for us. | ||
* We will learn the secret words that create and compel them. | * We will learn the secret words that create and compel them. | ||
| − | * Any little mistake in our incantations will result in our demons ceasing work and cursing | + | * Any little mistake in our incantations will result in our demons ceasing work and cursing us with dread error messages. |
* Thus, it behooves us to continually perfect our understanding of their demonic tongue and repair our program incantations where they show weakness. | * Thus, it behooves us to continually perfect our understanding of their demonic tongue and repair our program incantations where they show weakness. | ||
| Line 17: | Line 19: | ||
==The Mystery Of The Curly Braces== | ==The Mystery Of The Curly Braces== | ||
| + | Banner.java | ||
| + | <pre> | ||
| + | // This applet displays a message moving horizontally | ||
| + | // across the screen. | ||
| + | |||
| + | import java.awt.*; | ||
| + | import java.awt.event.*; | ||
| + | import javax.swing.*; | ||
| + | |||
| + | public class Banner extends JApplet | ||
| + | implements ActionListener | ||
| + | { | ||
| + | private int xPos, yPos; // hold the coordinates of the banner | ||
| + | |||
| + | public void init() | ||
| + | { | ||
| + | Container c = getContentPane(); | ||
| + | c.setBackground(Color.WHITE); | ||
| + | xPos = c.getWidth(); | ||
| + | yPos = c.getHeight() / 2; | ||
| + | Timer clock = new Timer(30, this); // fires every 30 milliseconds | ||
| + | clock.start(); | ||
| + | } | ||
| + | |||
| + | // Called automatically after a repaint request | ||
| + | public void paint(Graphics g) | ||
| + | { | ||
| + | super.paint(g); | ||
| + | g.drawString("Hello, World!", xPos, yPos); | ||
| + | } | ||
| + | |||
| + | // Called automatically when the timer fires | ||
| + | public void actionPerformed(ActionEvent e) | ||
| + | { | ||
| + | Container c = getContentPane(); | ||
| + | |||
| + | // Adjust the horizontal position of the banner: | ||
| + | xPos = xPos - 1; | ||
| + | if (xPos < -100) | ||
| + | { | ||
| + | xPos = c.getWidth(); | ||
| + | } | ||
| + | |||
| + | // Set the vertical position of the banner: | ||
| + | yPos = c.getHeight() / 2; | ||
| + | |||
| + | repaint(); | ||
| + | } | ||
| + | } | ||
| + | </pre> | ||
| + | |||
| + | * What do you notice about the braces and the words of this incantation? | ||
| + | |||
| + | Braces delimit '''blocks'''. A block is a series of statements, and statements are easy to spot because they usually are one per line and end with a semicolon. | ||
| + | |||
| + | * How many blocks are there in this incantation? | ||
| + | * How many statements are there in this incantation? | ||
| + | * Guess how many statements can be in a block: smallest number and largest number. | ||
| + | |||
| + | This incantation is called a '''class''' because it has the magic word '''class''' in it. Muggles call thes magic words '''reserved words'''. | ||
| + | |||
| + | There should be a program on your desktop called Dr. Java. | ||
| + | * Start Dr. Java. | ||
| + | * Cut and paste the incantation Banner.java into Dr. Java. | ||
| + | * Use the file menu to save it to your H drive. Don't change the name from Banner. Dr. Java automatically knows what to call the file: you just tell it what folder. | ||
| + | * Use the Edit/Preferences menu to check the "Show All Line Numbers" box. Click apply, and close the preferences box. Go "oooo, ahhhhhhh!" | ||
| + | * Click "compile", then click "run". | ||
| + | * Enjoy the results! | ||
| + | |||
| + | Now we play with it. | ||
| + | * Look for numbers, and try to change them to make it run differently. You will need to compile and run to see your changes. | ||
| + | * What numbers do what? | ||
| + | * Bonus if you can find how to make it hop instead of smooth scrolling. | ||
| + | * Double bonus if you can do it the right way. | ||
| + | |||
| + | Here is another incantation: | ||
| + | |||
| + | <pre> | ||
| + | // This program shows simple graphics in a window. | ||
| + | |||
| + | import java.awt.*; | ||
| + | import javax.swing.*; | ||
| + | |||
| + | public class HelloGraphics extends JPanel | ||
| + | { | ||
| + | public void paintComponent(Graphics g) | ||
| + | { | ||
| + | super.paintComponent(g); // Call JPanel's paintComponent method | ||
| + | // to paint the background | ||
| + | g.setColor(Color.RED); | ||
| + | |||
| + | // Draw a 150 by 45 rectangle with the upper-left | ||
| + | // corner at x = 25, y = 40: | ||
| + | g.drawRect(20, 40, 150, 45); | ||
| + | |||
| + | g.setColor(Color.BLUE); | ||
| + | |||
| + | // Draw a string of text starting at x = 60, y = 25: | ||
| + | g.drawString("Hello, Graphics!", 55, 65); | ||
| + | } | ||
| + | |||
| + | public static void main(String[] args) | ||
| + | { | ||
| + | JFrame window = new JFrame("Graphics Demo"); | ||
| + | // Set this window's location and size: | ||
| + | // upper-left corner at 300, 300; width 200, height 100 | ||
| + | window.setBounds(300, 300, 200, 150); | ||
| + | window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); | ||
| + | |||
| + | HelloGraphics panel = new HelloGraphics(); | ||
| + | panel.setBackground(Color.WHITE); // the default color is light gray | ||
| + | Container c = window.getContentPane(); | ||
| + | c.add(panel); | ||
| + | |||
| + | window.setVisible(true); | ||
| + | } | ||
| + | } | ||
| + | </pre> | ||
| + | |||
| + | This incantation has not followed the rules of the curly braces, but will still work. | ||
| + | |||
| + | * Cut and paste it into Dr. Java, and save it as HelloGraphics. | ||
| + | * Run it: it should work. | ||
| + | * Now indent it properly so that it looks like Banner.java above. | ||
| + | * Run it: it should still work. | ||
| + | * What does that tell us about spaces in these incantations? | ||
| + | * Why then do we indent according to curly braces? | ||
| + | |||
| + | Let's do it the easy way now! | ||
| + | |||
| + | * Cut and paste it again into Dr. Java, so there is no indentation. | ||
| + | * Select all the code. | ||
| + | * Press the Tab key. What magic has resulted? | ||
| + | * If you have time, you can play with this program too. | ||
