CITA 140 Introduction To Computer Programming

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CITA 140 Introduction To Computer Programming

• Instructor Dr. Douglas Dune, Ph.D.

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Java Programming, Third Edition

• Chapter One
• Creating Your First Java Classes

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Objectives

• Learn about programming
• Be introduced to object-oriented programming
  concepts
• Learn about Java
• Analyze a Java application that uses console
  output
• Add comments to a Java class

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Objectives (continued)

• Save, compile, and run a Java application
• Modify a Java class
• Create a Java application using GUI output
• Correct errors and find help

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Learning About Programming

• Program set of instructions directing computer
  action
• Machine language based on circuit switching
• High-level programming languages
• Languages approximating natural language syntax
• Example terms read, write, and add
• Syntax grammatical rules of programming language

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Learning About Programming (continued)

• Compiler translates high-level code into object
  program
• Interpreter converts and executes statements
  line by line
• Debugging locating and repairing errors
• Program logic structural integrity

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Introducing Object-Oriented Programming Concepts

• Procedure set of operations forming program unit
• Variable named computer memory location
• Procedural programming
• Procedure acts on separate data to perform
  task(s)
• Procedure may call or invoke other procedures
• Object-oriented programming
• Views application as a set of interacting objects
• Objects contain data and methods

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Introducing Object-oriented Programming Concepts
(continued)

• Three OOP language requirements
• Encapsulation, inheritance, polymorphism
• Class object template encapsulating methods and
  data
• Object components
• Attributes (states) defining characteristics
• Methods self-contained blocks of program code
• Instance term for an existing object of a class

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Introducing Object Oriented Programming Concepts
(continued)

• Inheritance class deriving methods/data from
  another
• Example Mustang derives features from generic
  Ford
• Polymorphism method operation specified by
  context
• close ( ) interpreted differently by printer and
  browser

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Learning About Java

• Java was developed by Sun Microsystems
• Object-oriented language modeled after C
• Designed for interactive Web-based applications
• Also suitable for general purpose applications
• Java is architecturally neutral
• Java is compiled and interpreted
• Source code form of Java (and all high-level)
  programs

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Learning About Java (continued)

• Java programs run on Java Virtual Machine (JVM)
• Three step process from source code to executable
• Source code written in text editor
• Java compiler translates into bytecode (binary
  program)
• Java interpreter executes line by line in JVM

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Java Program Types

• Java applets programs embedded in a Web page
• Java applications stand-alone programs
• Console support character output to DOS window
• Windowed create GUIs (graphical user interfaces)
  

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Analyzing A Java Application That Uses Console
Output

• Console applications relatively easy to write
• The First class is written on seven lines
• First's sole task output "First Java
  Application"

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Understanding the Statement That Prints the
Output

• Literal string character sequence enclosed by "
  "
• Argument data passed to a method
• Parsing System.out.println("First Java
  Application")
• out is a System object
• println ( ) is a method encapsulated in out
• Dot operator separates class, object, method
• println ( ) takes literal string argument
• println( ) outputs string, places cursor on next
  line

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Understanding the First Class

• All coding takes place within classes
• Class defined by using name or identifier
• Identifiers must meet four requirements
• Contain letters, digits, underscores, or dollar
  signs
• Begin with a letter, underscore, or dollar sign
• May not be a Java reserved keyword, such as class
• May not be primitive value true, false, or null
• Convention begin class name with uppercase letter

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Understanding the First Class (continued)

• First line public class First
• Keyword class identifies First as a class
• Public access modifier defining permissions
• Contents enclosed within curly braces
• Includes main ( ) method
• main ( ) method encloses another method, println(
  )

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Understanding the Main Method

• Parsing public static void main(String args)
• public defines access level (least restrictive)
• static indicates method independent of object
• void indicates method does not return a value
• String indicates argument type (string class)
• The name args is a placeholder for argument
• class First may be used as a shell (or template)
• Replace println( ) with block comments

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Adding Comments To A Class

• Comments non-executing lines documenting program
• Statements "commented out" ignored by compiler
• Three ways to comment
• Line comments //
• Block comments / /
• javadoc comments / /

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Saving a Java Class

• Java class stored in secondary memory (disk)
• Save public class with .java extension
• Example First.java
• Class name and file name must match
• Java is case-sensitive

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Compiling a Java Class

• Two-step translation process
• Source code compiled into bytecode
• Bytecode interpreted into executable statements
• Compiling at the command line
• Source code file should be in path
• Type javac followed by name of file
• Example javac First.java
• Syntax errors require debugging in text editor

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Running a Java Program

• Running application
• Type java followed by class name
• Example java First
• Application output appears in command window

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Modifying a Java Class

• To produce new output, modify text file
• Open text file that contains existing program
• Change original literal string
• Add an additional literal string with new println
  ( )
• Save file with changes (under same name)
• Recompile class with javac command
• Interpret bytecode and execute using java
  command

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Creating A Java Application Using GUI Output

• JOptionPane provides dialog boxes for GUI output
  
• Implementation
• Import class package containing JOptionPane
• Example import javax.swing.JOptionPane
• Use showMessageDialog( )
• Like println ( ), but with two arguments
• Pass null and new literal string
• Must use exit ( ) method to return control to OS

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Correcting Errors and Finding Help

• Syntax errors
• Concern violation of language rules
• Captured and highlighted by compiler
• Logic error
• Syntactically correct, but semantically invalid
• Captured at run-time by operating system (crash)
• Example class ErrorTest
• Comments in second line not properly closed

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Correcting Errors and Finding Help (continued)

• After debugging error, program recompiled
• Java resources at http//java.sun.com
• Documentation
• Java API (class library)
• FAQs (Frequently Asked Questions)
• SDK (Java Software Development Kit)
• The Java Tutorial

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Summary

• OO features encapsulation, inheritance,
  polymorphism
• OO programs consist of interacting objects
• Object is an instance of a class
• Objects encapsulate methods and attributes
• Java object-oriented programming language

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Summary (continued)

• All Java coding in the context of classes
• Java architecturally neutral
• Java source code compiled into bytecode
• Java interpreter executes bytecode within JVM
• Java program types applets and applications

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Summary (continued)

• Syntax grammatical rules of language
• Logic program semantics
• Comments non-executable documenting statements
• Compilation command javac fileName.java
• Run command java fileName