1 / 16

Chapter 2

Chapter 2. Programming by Example. A Holistic Perspective. Three sections separated by blank lines. Program comment File: FileName.java -------------------------- What the program does Imports Library packages Main class. Program Comment Format. /* * File: HelloProgram.java

delu
Download Presentation

Chapter 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 2 Programming by Example

  2. A Holistic Perspective Three sections separated by blank lines. • Program comment File: FileName.java -------------------------- What the program does • Imports Library packages • Main class

  3. Program Comment Format /* * File: HelloProgram.java * ----------------------------------- * Describe what this program does. Inputs and outputs * if any. The user can run this program without reading * the code. * * Author: E. Roberts, 123456 */

  4. Main Class Format public class HelloProgram extends GraphicsProgram { public void run() { add(new GLabel(“hello, world”, 100, 75)); } } • Indentations (3 spaces each level) • Positions of “{“ and “}” • ClassName and methodName

  5. Main Class public class HelloProgram extends GraphicsProgram { body of the class definition } • Key words: public, class, extends • Main class name must be the same as file name • Main class HelloProgram is a subclass of GraphicsProgram, defined in acm.program package (must be imported).

  6. Body of Main Class public void run() { add(new GLabel(“hello, world”, 100, 75)); } • run: method name • run(): no arguments passed to run • add: method defined in acm.graphics, one argument (an object of GLabel class) • GLabel: a class defined in acm.graphics, requires three arguments

  7. Out put: 75 Hello, world 100 Hello, world

  8. Add Two Integers /* * File: Add2Integers.java * ------------------------------- * This program prompts for two integers, adds them, and prints their sum. * * Author: E. Roberts, 123456 */ Import acm.program.*; public class Add2Integers extends ConsoleProgram { public void run() { println(“This program adds two integers.”); int n1 = readInt(“Enter n1: “); int n2 = readInt(“Enter n2: “); int total = n1 + n2; println(“The total is “ + total + “.”); } }

  9. Questions • Add2Integers is a subclass of what class? • Where is ConsoleProgram (handles console input and output) class defined? • Where are the methods println and readInt defined? • run() is a method in which class?

  10. Console Output • println: displays the argument string then returns to next line println(“This program adds two integers.”) Displays: This program adds two integers. println(“The total is “ + total + “.”) Displays, when the value of total is 42, The total is 42. • +: concatenation operator

  11. Console Input • readInt: displays argument string, prompts an integer entered from keyboard, returns the entered integer. readInt(“Enter n1: “) Displays Enter n1: prompts an integer from keyboard, if 17 is typed, Enter n1: 17 returns 17

  12. HelloProgram Revisited Split add(new GLabel(“hello, world”, 100, 75)); Into GLabel msg = new GLabel(“hello, world”, 100, 75); add(msg); Why? Control font, size, color, etc, in between. How?

  13. Sending Messages Setting font-size and color public void run() { GLabel msg = new GLabel(“hello, world”, 100, 75); msg.setFont(“Helvetica-24”); msg.setColor(Color.RED); add(msg); } hello, world

  14. GRect and GOval /* * File: GRectPlusGOval.java * ------------------------------------ * This program draws a red rectangle and a black * outlined and green filled oval */ import acm.graphics.*; import acm.program.*; import java.awt.*;

  15. GRect and GOval (cont.) public class GRectPlusGOval extends GraphicsProgram { public void run() { GRect rect = new GRect(100, 50, 125, 60); rect.setFilled(true); rect.setColor(Color.RED); add(rect); GOval oval = new GOval(100, 50, 125, 60); oval.setFilled(true); oval.setColor(Color.GREEN); add(oval); } }

  16. position: ( 100, 50) width: 125 height: 60 unit: pixel

More Related