COP3252 Advanced Java Programming

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COP3252Advanced Java Programming

• 10-Jan-08
• Lecture Set 2
• Intro Java History, Java vs C, compiling and
  running, Printing Text, Assignment 1

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History of Java

• 1991 Sun Microsystems funds internal corporate
  research project (Codename Green)
• Goal is to gain a stake in the growing
  intelligent consumer-electronic device sector
• Results in C based language
• Creator, James Gosling, named language Oak
• Sun realizes that Oak is already taken
  renames langauge Java while at a coffee shop

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History of Java

• Early 90s Green project has a slow start
• Market for intelligent consumer-electronic
  devices was slow to develop
• Project is in danger of being canceled
• Mid 90s WWW explodes in popularity
• Sun sees potential for using Java to add dynamic
  content (interactivity, animations ) to web
  pages.
• Green project comes alive again
• May 1995 Sun Microsystems officially announces
  Java at an industry conference.
• Today Java is used to provide applications on
  many consumer devices (cell phones, gaming
  systems, pdas, etc)

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Java vs. C

• Compiling and Running
• C
• Must be fully compiled into machine language
• Resulting executable is machine-specific
• Portable only when using non-machine specific
  libraries (but still requires compilation on each
  platform)
• Generally faster run-time for executable
• Java
• Compiled into bytecode (not into machine
  language)
• Bytecode runs on an interpreter (Java Virtual
  Machine)
• Bytecode is portable but JVM must be installed
  on platform
• Reduced runtime speed since it had to run through
  an interpreter

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Benefits of Java

• Software development kit (SDK) includes vast
  collection of packages (classes)
• Easy-to-use API (on Suns website)
• Standard format for building API docs (Java Docs)
• Very easy to build GUIs
• Runs on multiple platforms
• No pointer notation
• Objects and arrays are created dynamically
• Automatic garbage collection / memory management

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Benefits of C

• C gives the programmer more control (resource
  allocation/deallocation, control over addresses
  with pointers)
• Programs run faster (compiled with platforms
  native instructor set, no interpreter)

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Java Class Libraries

• Java programs consist of pieces call classes
• Classes include pieces call methods
• Methods perform tasks and return information
• Many existing classes exist in the Java
  Application Programming Interface (API)
• Learning Java is a combination of learning the
  language (to write your own classes) and learning
  about the classes already available in the Java
  class library.

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The Java Hello World File

• public class example
• public static void main( String args )
• System.out.println(Hello, World.)

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Hello World explanation

• public class example
• Begins the class declaration for class example
• Every program in Java consists of at least one
  class declaration (defined by the programmer)
• class is a reserved word in Java it begins
  the class declaration and expects a class name to
  immediately follow
• Opening and closing brackets are used to
  denote the start and end of the class

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Class Naming

• By convention, all class names in Java begin with
  a capital latter and capitalize the first letter
  of each word they include
• Example MyClassName
• Class names are indentifiers
• String of characters consisting of letters,
  digits, underscores, and dollar signs
• Do no being with a digit and can not contain
  spaces
• Note JAVA IS CASE SENSITIVE
• Test is not the same as test

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Class Naming public and filenames

• Example begins with word public
• This keyword will be used (for now) when defining
  all of our classes . But will not be explained
  until later
• When declaring a class public, we are required
  to name the source code file with the same name
  as the class.

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Hello World explanation

• public static void main (String args)
• main method declaration
• Starting point for every Java application
• JVM will not execute the application if the above
  line is not present
• All method bodies open with a and close with a

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Hello World explanation

• System.out.println(Hello, world.)
• One of Javas command line print statements
• Instructs Java to print a String to the command
  line.
• Calls the println function standard output
  object.
• Moves cursor to next line in the command window.
• Strings in Java are denoted by a set of opening
  and closing double quotes
• All statements end with a semicolon.

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Creating your first .java file

• Open an editor on one of the CS machines and
  input the source code
• Save the file as example.java
• Exit your text editor
• Now you will compile (make the code executable)
  from the command line

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Compiling a JAVA Program

• JAVA compiler command javac
• should be a valid .java file
• If there are no errors, the compiler will create
  your object code (.class file)
• If there are errors, the compiler will return a
  list of line numbers and the corresponding error
  messages.

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Compiling an error free JAVA program

• Create a file called example.java using the code
  from an earlier slide
• Compile the program with the command javac
  example.java
• Use the ls command to verify that the compiler
  has created an example.class file

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Running a Compiled JAVA Program

• The command to execute a compile program is
  java
• is the name of the class of the
  program you wish to run OR the name of the
  .class file without the .class extension
• Example To run example.class, you would type
  java example

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Submitting a Program

• Use the Digital Dropbox on Blackboard
• Student tools - Digital Dropbox
• Click the send file button
• Fill in the name
• Click the choose file button to find your file
• Click the submit button

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The Java JRE and SDK

• Both are available from http//java.sun.com
• JRE (Java Runtime Environment) Allows you to
  run already compiled programs (.class files) on a
  system
• SDK (or JDK Java Development Kit) Allows you
  to compile and run Java programs (includes the
  JRE)
• The JRE and JDK is available for all popular
  operating systems.
• The JDK must be installed on your personal
  machine if you wish to use an IDE such as
  NetBeans, JCreator, JGrasp, or Eclipse.

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JAVA Comments

• Comments are used to document the code and import
  the readability.
• There are two types of comments in JAVA
• Single-line comments line begins with //
• Example
• //This is a single-line comment
• Multi-line (or block) comments begins with /
  and ends with /
• Example
• / This is a
• multi-line comment/

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JAVA Comments Example

• /Name R. Thornton
• Date 16-Jan-07
• Program Comment Example/
• //Begin example class
• public class example
• //Begin main method
• public static void main (String args)
• System.out.println(Hello) //Print a string
• //end main method
• end example class

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JAVA Comments

• You MUST comment all of your code in this course.
• Proper commenting will account for 10 to 20 of
  each program assignment grade.
• Commenting guidelines
• It is recommended that you include enough
  comments in your code so that someone completely
  unfamiliar with programming can read through your
  code and figure out what it is doing.
• It is better to have too many comments than to
  not have enough comments!

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Programming Style

• A portion of every assignment grade will be based
  on your programming style.
• Programs should be easy to read and properly
  indented
• Examples of proper indentation will be show in
  all example code given in this class.

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JAVA Printing text to the screen

• We use the standard output object to print text
  in to the screen.
• There are two standard output object methods
• System.out.print(a string)
• Prints the string and leaves the cursor on the
  same line
• System.out.println(a string)
• Prints the string and moved the cursor to the
  next line

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JAVA Printing text to the screen Cont.

• These two methods take a string as input.
• The input of a method is denoted by an opening
  and closing parenthesis ( and ).
• A string is denoted by an opening and closing set
  of double-quotes and
• Anything between the quotes is printed as-is
• except for escape sequences (discussed later)
• The end of a line of code is denoted by a
  semi-colon

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JAVA Printing text to the screen Cont.

• The following code
• System.out.print(Hello.)
• System.out.println( Welcome to)
• System.out.println(JAVA)
• Prints this to the screen
• Hello. Welcome to
• JAVA
• _

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JAVA Printing text to the screen Escape
Sequences

• JAVA has a list of escape sequences that
  represent special formatting options
• The backslash (\) is an escape character and
  denotes the start of an escape sequence.
• The character immediately following the backslash
  determines which escape sequence will be used.

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JAVA Printing text to the screen Escape
Sequences
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JAVA Printing text to the screen Example

• print, println, and escape sequence examples can
  be found in the PrintExamples.java file on the
  course website

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Assignment 1 / Next Class

• See assignments page.
• Due Tuesday, 15th of Jan, 2008.
• Assignment 2 will be assigned on Tuesday.
• Also on Tuesday
• Variables, printf, control structures