Software Development Using Java

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Software Development Using Java

• Surgery
• Peter King
• Cathy French

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Timetables

• make sure you are attending
• 2 lecture slots
• 2 tutorial slots
• 1 surgery (this one)

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For discussion

• What programming language(s) have you studied
  before?
• What differences have you noticed so far?

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Java vs. Visual Basic .NET

• both are programming languages
• with standard programming language features
• variables, data types, sequence, selection,
  iteration, methods (functions)
• both are object-oriented
• all code belongs to a class
• large applications will have many classes
• usually we construct objects of these classes
• easier to manage large programs
• each form in Visual Basic .NET is a different
  class
• can also write classes for non-GUI objects
• Spike

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Java vs. Visual Basic .NET

• both compile to platform-neutral code
• Java byte-code
• .NET - Microsoft Intermediate Language
• C and J also compile to MSIL
• both are executed using an interpreter
• Java Virtual Machine
• .NET Common Language Runtime
• need a different interpreter for each platform
• Window, Linux, Solaris SPARC, Solaris x86 etc.

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Java vs. Visual Basic .NET

• extensive and easy to use class libraries
• Java Application Programming Interface (Java API)
• .NET Framework Class libraries
• web applications
• networking sockets
• graphical user interfaces
• mobile devices
• data structures
• database connections
• already written
• programmer has to learn how to use them

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Java vs. Visual Basic .NET

• both support rich Graphical User Interfaces
• Visual Basic commonly takes GUI-first approach
• use Visual Studio Integrated Development
  Environment (IDE)
• drag and drop GUI components
• autogenerate code skeleton
• type in method bodies by hand
• type in non-GUI classes
• in this module we will take a code-first approach
• type in most code by hand
• so we can understand it
• but drag-and-drop IDEs are available for Java
• Borland JBuilder, Together, NetBeans

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Why study Java?

• to learn another language
• widely used, especially in networked applications
• build on and reinforce the programming
  fundamentals you learnt in study of Visual Basic
• same ideas expressed in different syntax
• keywords, use of brackets, comments
• use of different libraries
• GUI components, String handling

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A first Java program

• / A first Java program /
• public class HelloApp
• public static void main(String args)
• String name
• // declares a variable called name of type String
• name "Cathy"
• System.out.println("Hello, " name)

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HelloApp in detail

• all Java code must belong to a class
• each application (program) must contain at least
  one class
• this application has only one class called
  HelloApp
• the code for each class is stored in a file with
  the same name
• with the extension .java
• our file is called HelloApp.java

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Declaring the class

• start with a class declaration
• public class HelloApp
• body (content) of the class follows within curly
  brackets
• indent body for readability
• public and class are Java keywords
• have specific meaning
• reserved by Java
• dont use them for your own variable, attribute
  or method names!

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The main method

• all Java programs must have a main method
• program execution starts here
• statements in main method are executed
  sequentially until closing is reached
• Visual Basic programs also have an Main procedure
• generated automatically when you create a project
• usually loads the first form
• main method always has the same signature
• public static void main(String args)

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Java statements

• each statement
• represents an action
• ends with a semicolon
• String name
• declares a variable of type String called name
• name "Cathy"
• stores the value "Cathy" in name
• System.out.println("Hello, " name)
• prints the text in brackets in the console window

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Outputting text

• Java provides methods to output text to the
  console window in the class System.out
• this is a library class that is part of the Java
  language
• System.out.println(name)
• prints out the String stored in the variable name
• then goes to a new line
• System.out.print(name)
• prints out what is stored in name
• but does not start a new line

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Outputting text

• System.out.print("Hello")
• prints the word "Hello"
• can print more than one item by putting between
  them
• System.out.println("Hello, " name)
• use escape sequences for formatting
• /n new line
• /t tab
• /" double quote mark
• System.out.println("Hello \n Welcome")
• System.out.println("\tYou must be \"Cathy\"")

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Comments

• ignored by compiler
• can write whatever you want
• // single line (or end of line)
• / multiple line comments go here
• everything between the marks
• is ignored /
• important for documentation!!!!
• useful to comment out suspect code
• don't delete it
• put / / around it

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Typical program structure

• // any import statements
• public class TypicalApp
• public static void main(String args)
• // declare variables
• // assign variable values
• // (perhaps with input from user)
• // do processing / calculations
• // output results