Professor: Alvin Chao

Transcription

1 Professor: Avin Chao

2 Anatomy of a Java Program: Comments Javadoc comments: /** * Appication that converts inches to centimeters. * Chris Mayfied 01/21/2014 */ Everything between /** and */ ignored by compier Used to generate code documentation

3 Anatomy of a Java Program: Comments Bock comments are used for text that shoud not be part of the pubished documentation: /* */ Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation fies (the "Software"), to dea in the Software without restriction. In-ine comments are used for short carifying statements: // Create a scanner for standard input.

4 Anatomy of a Java Program: Casses Java is an object-oriented anguage (OO) - Java casses tie together instructions and data - A Java code must exist within some cass pubic cass ConvertInches { pubic and cass are keywords: Words that have a specia meaning for Java. - pubic (more ater) - cass Create a cass with the foowing name. (Must match the fie name) - Cass names are aways captaized Braces { and encose bocks of code

5 Anatomy of a Java Program: Methods Method named coection of Java statements: pubic cass ConvertInches { pubic static void main(string[] args) { Later

6 Anatomy of a Java Program: Methods Method named coection of Java statements: pubic cass ConvertInches { pubic static void main(string[] args) { Later return type (void means nothing is returned)

7 Anatomy of a Java Program: Methods Method named coection of Java statements: pubic cass ConvertInches { pubic static void main(string[] args) { Later return type (void means nothing is returned) method name main is the starting point for a Java programs

8 Anatomy of a Java Program: Methods Method named coection of Java statements: pubic cass ConvertInches { pubic static void main(string[] args) { Later return type (void means nothing is returned) method name main is the starting point for a Java programs argument type String[] means that this method takes an array of Strings.

9 Anatomy of a Java Program: Methods Method named coection of Java statements: argument name args wi be an array of Strings from the command ine. args[0], args[1], etc. pubic cass ConvertInches { pubic static void main(string[] args) { Later return type (void means nothing is returned) method name main is the starting point for a Java programs argument type String[] means that this method takes an array of Strings.

10 Anatomy of a Java Program: Decaring and Assigning Variabes variabe named box for storing data: type Defines what the variabe can hod name Shoud aways be informative. x is not OK. int inch; doube cent; fina doube CENT_PER_INCH; CENT_PER_INCH = 2.54;

11 Anatomy of a Java Program: Decaring and Assigning Variabes variabe named box for storing data: type Defines what the variabe can hod name Shoud aways be informative. x is not OK. int inch; doube cent; fina doube CENT_PER_INCH; CENT_PER_INCH = 2.54; assignment Puts the vaue on the right into the variabe on the eft. ALWAYS RIGHT TO LEFT! itera vaue

12 Anatomy of a Java Program: Decaring and Assigning Variabes variabe named box for storing data: type Defines what the variabe can hod name Shoud aways be informative. x is not OK. fina makes this variabe a constant int inch; doube cent; fina doube CENT_PER_INCH; CENT_PER_INCH = 2.54; assignment Puts the vaue on the right into the variabe on the eft. ALWAYS RIGHT TO LEFT! itera vaue

13 Anatomy of a Java Program: Standard Library and Keyboard Input import java.uti.scanner; /** * Appication that converts inches to centimeters. * Chris Mayfied 01/21/2014 */ pubic cass ConvertInches { import Brings in externa casses pubic static void main(string[] args) { int inch; doube cent; fina doube CENT_PER_INCH; CENT_PER_INCH = 2.54; // Create a scanner for standard input. Scanner keyboard; keyboard = new Scanner(System.in); The Scanner cass, aong with System.in are used to read user input from the termina // Prompt the user and get the vaue. System.out.print("How many inches? "); inch = keyboard.nextint();

14 Putting it a together... import java.uti.scanner; /** * Appication that converts inches to centimeters. * Chris Mayfied 01/21/2014 */ pubic cass ConvertInches { pubic static void main(string[] args) { int inch; doube cent; fina doube CENT_PER_INCH; CENT_PER_INCH = 2.54; // Create a scanner for standard input. Scanner keyboard; keyboard = new Scanner(System.in); // Prompt the user and get the vaue. System.out.print("How many inches? "); inch = keyboard.nextint(); mutipication + joins strings (or adds numbers) // Convert and output the resut. cent = inch * CENT_PER_INCH; System.out.print(inch + "in = "); System.out.printn(cent + "cm ");

15 Reminder: Portabiity Most high-eve anguages are considered portabe because they can be compied into machine code for any computer: x86 Compier x86 Program C Program ARM Compier ARM Program

16 Java Compiation Byte Code Fies are portabe because there are JVM's that run on most machines The same compied byte code works on any JVM

17 Which is Syntacticay Correct? pubic static void main(string[] args) { System.out.printn("Heo " + args[0] + "!"); System.out.printn("Wecome to CS149."); pubic cass Persona { pubic static void main(string[] args) { System.out.printn("Heo " + args[0] + "!"); System.out.printn("Wecome to CS149."); pubic cass Persona { // pubic static void main(string[] args) { System.out.printn("Heo " + args[0] + "!"); System.out.printn("Wecome to CS149.");

18 pubic cass Wecome { pubic static void main(string[] args) { String name; name = "Bob"; System.out.printn("Heo " + name + "!"); System.out.printn("Wecome to CS149."); Which is Syntacticay Correct? (Fie name is Good.java) pubic cass Good { pubic static void main(string[] args) { String name; "Bob" = name; System.out.printn("Heo " + name + "!"); System.out.printn("Wecome to CS149."); pubic cass Good { pubic static void main(string[] args) { String name; name = "Bob"; System.out.printn("Heo " + name + "!"); System.out.printn("Wecome to CS149.");

19 Which is Syntacticay Correct? pubic cass Good pubic static void main(string[] args) { String name; name = "Bob"; System.out.printn("Heo " + name + "!"); System.out.printn("Wecome to CS149."); pubic cass Good { pubic static void main(string[] args) { String name; name = "Bob"; System.out.printn("Heo " + name + "!") System.out.printn("Wecome to CS149."); pubic cass Good { pubic static void main(string[] args){ String name; name = "Bob"; System.out.printn("Heo " + name + "!"); System.out.printn("Wecome to CS149.");

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