Java Programming

1
Java Programming

• CIS 421
• Web-Based Java Programming

2
Course Text

• Text
• Computing with Java
• Programs, Objects, Graphics
• Alternate 2nd Edition
• Art Gittleman
• Scott Jones Publishers
• ISBN 1-57676-074-X

3
Prerequsites, Tests, Public area

• Prerequisites
• Cis237, Mat 126, and QPA of 2.90
• Tests Two midterms, one final.
• Public directory
• /export/home/public/spiegel/cis421

4
Turnin script

• Programming Projects are submitted electronically
  using turnin script
• See turnin handout
• Must setup turnin once
• To invoke
• turnin421 ltfile1gt ltfile2gt ....
• each item submitted separated by whitespace
• no limit to items
• You should receive a confirmation e-mail
  containing an
• ls l listing of files submitted (can include
  files previously submitted)
• Files submitted may be overwritten by subsequent
  turnin of files with same name

5
Overview of Java

• Java Features
• How Java Works
• Applications vs Applets
• Program-Driven vs Event Driven
• Graphical User Interfaces (GUI)

6
Java Features

• Simple, Object-Oriented, Familiar
• Robust and Secure
• Architecture Neutral and Portable
• High Performance
• Interpreted, Threaded, and Dynamic

7
Simple, OO, Familiar

• Its simplicity comes from the fact that there are
  no pointers in Java. Therefore, the programmer
  does not have to manage pointers and the
  resultant problems that pointers bring.
• All programs in Java are based on objects
• Java uses the familiar syntax and fundamental
  control structures of C/C

8
Robust and Secure

• Robust programs run without crashing due to
  programming errors, erroneous input, or failure
  of external devices. Java has many checks at
  compile-time and provides run-time exception
  handling to deal with unexpected events.
• Security, especially across the internet,
  requires careful measures, which are implemented
  in Java

9
Architecture Neutral and Portable

• Java programs run on a variety of processors
  using various operating systems
• Portability depends not only on architecture but
  also on implementation. Java specifies the
  language carefully to reduce implementation
  dependencies.

10
High Performance

• Java versions continually increase performance
  capabilities.
• In network applications, communication delays
  usually far exceed performance delays.

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Interpreted, Threaded, and Dynamic

• Interpreted, not compiled.
• Threaded capable of multi_tasking and
  concurrent processing, even across the internet
• Dynamic linking to library code as it needs it.
• Java is ideally suited for general, interactive,
  and network programming

12
How Java Works
Java Compiler
Java Source Code
Java Byte Code
Java Interpreter For Processor 1
Java Interpreter For Processor 2
13
Setting up Unix for Java

• Make a directory called java in your home
  directory.
• Put this java directory in your CLASSPATH in
  .cshrc with the command (this is one long line)
• setenv CLASSPATH .home/javawhatever_is_there
  _already
• this allows packages starting from your java
  subdirectory
• Put the directory /usr/j2sdk1.4.0_03/bin in your
  path variable in the .login file.
• Give the commands source .login and source .cshrc
  to make the changes effective.
• These changes are applied automatically on
  subsequent logins

14
Testing Changes

• acad gt java -version
• java version "1.4.0_03"
• Java(TM) 2 Runtime Environment, Standard Edition
  (build 1.4.0_03-b04)
• Java HotSpot(TM) Client VM (build 1.4.0_03-b04,
  mixed mode)
• acad gt

15
Applications vs Applets

• Applications run like programs written in other
  languages. They usually are standalone, running
  at the command line.
• Applets are usually small applications that are
  embedded in a web-page and run on the internet in
  a web browser.

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Building an Application

• Edit the source file either in your favorite
  editor, or IDE, and save it as ltfilegt.java
• The file name must be the same as the one and
  only public class name in the file
• Compile by giving the command
• javac ltfilegt.java
• at the command line of a DOS or Unix window.
• Run the program by giving the command
• java ltfilegt

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hello.java

• // File hello.java
• // Compiler Sun javac
• // Compile javac hello.java
• // Executable hello.class
• // Execute java hello
• //
• // Purpose Prints usual first
• // program

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hello.java

• public class hello
• public static void main(String args)
• int x 3
• System.out.println(Hello, World!
• \nx (x) )

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Application Programs

• The file name must be the same as the one and
  only public class in the file.
• This public class must have a static method
  called main (Why static??)
• public static void main( String args)
• local declarations and statements

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Exercise

• Setup your Unix account to compile and run a Java
  Application program. Test it with the HelloWorld
  program hello.java.
• The example is in the java/hello subdirectory in
  the instructors public area

21
Basic Java Programming

• The C/C component
• Comments C/C style
• Identifiers and keywords
• Types, variables, expressions
• Control structures
• Functions
• System output
• Console input
• Packages

22
Identifiers and Keywords

• A Java identifier must start with a letter,
  followed by 0 or more letters and/or digits.
  Java is case-sensitive.
• Keywords cannot be used as user-identifiers. See
  text for a list of keywords.
• Style recommended preferred consistency is a
  must!
• Class names begin with a capital letter
• Variable names begin with a lower case letter
• Function names begin with a verb which is
  lowercased.
• Constants are all upper case.
• Multiple word names are lower case except for the
  beginning of each word component.

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Examples

• Request would be a class name
• myRequest would be a variable name
• getRequest() would be a function (method) name
• THE_REQUEST would be a constant.
• The Java standard style convention should be
  followed in our programming.

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Standard Types

• char ascii or unicode
• boolean true or false
• Numerical types various sizes of numbers

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Numerical Types

• Standard numerical types in Java are
• type size least value greatest value
• ________________________________________
• byte 8 -128 127
• short 16 -32768 32767
• int 32 -2147483648 2147483647
• long 64 -263 263-1
• float 32 -3.4 x 1038 3.4 x 1038
• double 64 -1.7 x 10308 1.7 x 10308
• 7 and 15 digit accuracy respectively

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Variables and Expressions

• Java follows the syntax of C/C for expressions
  and assignment.
• The operators for the standard types are the same
  as those for C/C
• Remember that is assignment and
• is equal relational operator.
• You should NOT use in a cascading manner.

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Control Structures

• The control structures are the same as C/C
• if
• switch
• for
• while
• do while
• Note unlike C/C, where the expression can
  evaluate to int, the test expression MUST be of
  type boolean

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Functions (Methods)

• In Java there are no independent functions
• A function (method) is always a member function
  of some class.
• The syntax is very similar.
• modifier(s) resulttype name( ltparamsgt)
• local declarations
• and statements
• // the modifier is public, private, or
  protected, and can also be prefaced static

29
System Output

• Output is generated by using streams. The stream
  classes are defined in the standard Java package
  java.io.
• The class System in the package java.lang
  contains three different streams for use in Java
  programs
• System.in the keyboard
• System.out the screen
• System.err the screen
• System.out.println( any string)

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Examples of Output

• To print an object, the object should have
  overloaded the method toString that is inherited
  from the Class Object.
• Standard types have this method.
• System.out.println(The value of x x )
• The is the concatenation operator for strings.

31
System Input

• System input is quite complicated, so many
  authors provide a package of IO functions for the
  standard types.
• We prefer to avoid these. A class InputReader is
  in the public java directory for text input.
• More fundamental IO will be discussed later
• Java is made for GUIs, particularly components
  such as TextFields, Menus. etc

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Examples of input

• helloYou.java
• helloInt.java
• java/hello directory in public area

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Things that are different

• String concatenation is the operator
• It takes two operands which are stringable,
  that is any operand that is a string or has the
  toString method overloaded for that type.
• System.out.println(76 trombones)

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Packages

• Java organizes code into packages which
  correspond to directories in the file system.
• Each Java class is contained in a package.
• The default package is . (the current
  directory)
• The System class is found in java.lang
• The Applet class is found in java.applet

35
Comments

• When calling methods of the same class, we do not
  need to use the class name as a prefix.
• When calling methods of another class, we use the
  class name or object of that class as a prefix.

36
Objects

• Still declared as a class
• No separate sections
• Each declaration specified with access
• public, private, protected
• static declarations part of class, but not object
• non-static declarations part of instantiated
  objects only