Computer Science 1 (Studio) 01C-Simple Java

1. Computer Science 1 (Studio) 01C-Simple Java CS1s - 01C-Simple Java (v1.00)

2. Compilation in Java • The Java development toolchain: • Source code created with emacs has a .java extension • Byte code generated by javac has a .class extension • Byte code run by java excludes the extension % emacs Foo.java Other Java bytecode Foo.java Foo.class % javac Foo.java % java Foo Java Virtual Machine Java source code Java compiler Byte code CS1s - 01C-Simple Java (v1.00)

3. Basic Java Program FirstProgram.java: // This is my first program public class FirstProgram { public static void main (String args[]) { System.out.println(“Hello World!”); System.out.print(“I’m”); System.out.print(“ programming!”); } } CS1s - 01C-Simple Java (v1.00)

4. FirstProgram • The name of the program is FirstProgram • This source code must be contained in a file named FirstProgram.java • Some lines are terminated with curly braces { } while some are terminated with the semicolon ; • What’s the difference between: System.out.println() System.out.print() • “Literal strings are contained within double quotes.” • // Single line comments begin with forward slashes CS1s - 01C-Simple Java (v1.00)

5. Creating A Java Source Code File • In class Activity • Go to your ~/cs1/lec/01 directory • Create the FirstProgram.java file using emacs FirstProgram.java: // This is my first program public class FirstProgram { public static void main (String args[]) { System.out.println(“Hello World!”); System.out.print(“I’m”); System.out.print(“ programming!”); “What up!” } } CS1s - 01C-Simple Java (v1.00)

6. Compiling Java Programs • You must be in the same directory as the source code file, FirstProgram.java • ~/cs1/lec/01 • In class Activity • Compile your program using: % javac FirstProgram.java • There are two possible outcomes: • Your program compiled without any problems and the byte code, FirstProgram.class, was quietly generated • Error messages were printed to standard output and no byte code, FirstProgram.class, was generated CS1s - 01C-Simple Java (v1.00)

7. The Compiler • The java compiler is responsible for generating byte code from your java source code • Syntax errors in the source code cause the compiler to abort and display error messages • Missing symbols • Illegal instructions • Misspelled words • Your source code must be 100% syntactically correct before you can run your program CS1s - 01C-Simple Java (v1.00)

8. Fixing Syntax Errors • In class Activity • Load the source file into emacs • Locate the syntax error/s based on the compiler output • To go to a line number in emacs: Edit->Go To->Goto Line… • Make the necessary changes • Save the changes: File->Save (C-x C-s) • Recompile the source code using the same command: % javac FirstProgram.java • Repeat these steps until the compiler no longer reports any errors CS1s - 01C-Simple Java (v1.00)

9. Running Your Program • To run your program you must invoke the JVM in the same directory as the byte code file • This is the same directory as your source code • The JVM interprets the byte code which was generated by the compiler (FirstProgram.class) % java FirstProgram • In class Activity • Successfully execute the program CS1s - 01C-Simple Java (v1.00)

10. Coding Standards • Look again at the source code and answer the following questions: • Who is the author or authors of the code? • When was it written? • What is the purpose of the program? • What are the different working revisions and changes to the source? CS1s - 01C-Simple Java (v1.00)

11. Coding Standards • These questions cannot be answered because the program is not properly documented • Documentation is a very important part of writing code • It allows you or another author to interpret what you intended the code to do (in plain English) • It provides information about the author (ownership) • It documents what was done to the program • In a development group, consistent coding standards increases productivity CS1s - 01C-Simple Java (v1.00)

12. The DCS Coding Standard for Java • Each program you write in Java, to be submitted as coursework, must follow the DCS Coding Standard • Programs that work correctly, but are not properly documented, will be penalized when graded • In class Activity • Navigate to the Coding Standard link (under Documentation) on the CS1 Studio Homepage • Read through the rules for proper coding CS1s - 01C-Simple Java (v1.00)

13. Documenting FirstProgram • All source code must begin with a C-style comment that lists the file name and version information: /*  * filename.java  *  * Version:  *     $Id$  *  * Revisions:  *     $Log$  */ CS1s - 01C-Simple Java (v1.00)

14. Documenting FirstProgram • The following comments will appear before the definition of every class: /**  * A description of what the class does.  *  * @author      Author name  * @author      Contributor 2  * @author      Contributor 3                 .                 .  * @author      Contributor n  */ CS1s - 01C-Simple Java (v1.00)

15. Documenting FirstProgram • The following comments will appear before every method (including main):  /**   * A description of what the method does   *   * @param       name    description   …   * @param       name    description *   * @return              description *   * @exception   name    description …   * @exception   name    description */ CS1s - 01C-Simple Java (v1.00)

16. Documenting FirstProgram • In class Activity • Add a source file documentation block • Add a class definition block • Add a method header for the main method • Add a comment inside main to explain what is happening • Save the file, recompile and rerun CS1s - 01C-Simple Java (v1.00)

17. Writing your Second Program • In class Activity • Log on/off the CS system and get back into ~/cs1/lec/01 • Create a new Java source file called SecondProgram.java: public class SecondProgram { public static void (String args[]) { System.out.println(“Hello world!”) System.out.print(My name is ”); Systemout.println(“ YOUR NAME HERE ”; } • Save the file • Compile the program and make note of the errors • Correct all the errors in the program so that it successfully compiles and prints your name CS1s - 01C-Simple Java (v1.00)

18. Revision History • Revision History • v1.00, 9/2/2004 4:52 PM, sps Initial revision. CS1s - 01C-Simple Java (v1.00)