Overview of Java

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• Overview of Java
• programming projects for 3345

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Programming assignments submission

• .java files via WebCT, you may put them in one
  folder and archive them together
• readme.txt with instructions how to compile and
  run your code, format of the input, your
  assumptions, known bugs and limitations etc. Do
  not write program is self-explanatory, contact
  me with questions you may have.
• sample input and output files, if any
• makefile (optional)
• presentation of an assignment may be required,
  short questions may be asked

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Programming assignments development and coding

• Submit neat well-indented code, part of the grade
  is for code
• Provide enough comments (each variable (except
  loop iterators), function, block of code)
• For your own benefit, you may want to learn of
  javadoc or doxygen
• Follow good naming conventions
• Code optimization vs. development time and
  readability the example below is hard to read
• for(P("\n"),R-P(""))
• for(eCe-P("_"(u/8)2))P(""(u/4)2)

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Programming assignments development and coding

• Simple and working program is better than
  sophisticated and not working one. Bells and
  whistles go unnoticed when the basic
  functionality is poor.
• Develop with re-using in mind some of the
  routines of the first project (input\output, GUI)
  may be reused in the second project
• Always make backups and always keep a running
  copy of your code!
• If stuck in debugging, localize (isolate) errors
  comment all your code, insert only the Hello,
  world! line. See whether the program runs,
  gradually adding pieces of your code.

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Programming assignments run time issues

• Catch exceptions, exit gracefully, acknowledge
  exiting.
• One should be able to easily understand how to
  interact with the program, i.e. give meaningful
  labels to input fields, prompt for input in
  command-line interface.
• Program should be easy to use
• Dont hard-code the input data, yet you may use
  randomly generated numbers as the input

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Programming assignments

• It was agreed in class that the following
  environments are used to develop the projects
• NetBeans
• JBuilder
• JCreator
• Eclipse
• or text editor
• Please, stick to these options. Download the
  latest version of your favorite environment
  before you start.

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Using Unix machines

• Putty tool to connect to
• apache.utdallas.edu, ssh net01
• New rules net01-net50 machines cannot be used in
  this class
• javac to compile programs, java to run programs
• Makefiles and tarballs

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Honor code

• OK to use provided code examples
• No code from the book or web. If you need to use
  external code for some additional features,
  clearly specify the parts of the code that are
  not yours.
• Projects are individual. Explicitly acknowledge
  any cooperation.
• Using the standard Tree and Graph libraries is
  not allowed. Write your own classes corresponding
  to the objects.

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Java code concepts

• Source code written to .java
• Compiled using javac to .class
• A .class file does not contain code that is
  native to a given processor it instead contains
  bytecodes-- the machine language of the Java
  Virtual Machine. The Java launcher tool (java)
  then runs the application with an instance of the
  Java Virtual Machine.
• Platform hardware or software environment in
  which a program runs.
• Java platform software only
• 2 components
• The Java Virtual Machine
• The Java Application Programming Interface (API)

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Java platform

• One should have
• Java Runtime Engine (JRE) to run java
  applications
• Java Source Development Kit (SDK/JDK) to compile
  .java into .class
• Optionally, the development environment.

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Popular example

• package javalecture
• public class FirstClass
• public static void main(String args)
• System.out.println("I think therefore I think
  I am!")
• Try to explain the underlined terms before
  looking at the next slide.

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Package a unique namespace for the types it
contains classes in the same package can access
each other's protected members. Public class
is visible to all classes everywhere. No
modifier visible only within its own
package. Member (function) level Public, no
modifier same meaning Private can only be
accessed in its own class Protected can
only be accessed within its own package and, in
addition, by a subclass of its class in another
package. Instance methods are associated with
an object and use the instance variables of that
object. This is the default. Static methods
take all they data from parameters and compute
something from those parameters, with no
reference to variables. This is typical of
methods which do some kind of generic
calculation.
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Abstract classes and interfaces

• An abstract class is a class that is declared
  abstract and may include abstract
• methods (methods not implemented). Abstract
  classes cannot be instantiated,
• but they can be subclassed. In Java, EVERY class
  is a subclass of
• java.lang.Object (or subclass of its subclasses).
  
• abstract class Account
• int amount
• void withdraw(double number) ...
• abstract void changeBalance()
• An interface an abstract class declared as
  interface
• all variables are static and final
• only method signatures included, no method
  implementations.
• Interface PrintableObject
• static final Integer MaximumSizeInBytes256
• void print()

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Extends vs implements

• final class InterestBearingAccount extends
  Account
• Class InterestBearingAccount (subclass) inherits
  all members (variables and functions) of class
  Account (superclass).
• class Image implements PrintableObject
• Class Image provides implementation to methods of
  the class PrintableObject (e.g. method print()
  that would specify how exactly to print images).
• Interfaces are used to encode similarities which
  classes of various types share, but do not
  necessarily constitute a class relationship (e.g.
  Image and Text classes).
• A class which implements an interface must either
  implement all methods in the interface, or be an
  abstract class.

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Popular example using Swing

• package javalecture
• import javax.swing.JFrame
• import javax.swing.JLabel
• public class HelloWorld
• public static void main(String args)
• JFrame Frame new JFrame ("Hello,
  World!")
• Frame.setDefaultCloseOperation
  (JFrame.DISPOSE_ON_CLOSE)
• Frame.getContentPane().add (new
  JLabel("Hello, World!"))
• Frame.pack()
• Frame.setVisible(true)

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Draw with Swing

• import java.awt.
• import javax.swing.
• public class Drawing
• public static void main(String args)
• new Drawing()
• Drawing()
• JFrame frame new JFrame()
• frame.setDefaultCloseOperation(JFrame.DISPOSE
  _ON_CLOSE)
• frame.getContentPane().add(new MyComponent())
• frame.repaint()
• frame.setSize(300, 300)
• frame.setVisible(true)

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Draw with Swing
class MyComponent extends JComponent
public void paintComponent(Graphics g)
super.paintComponent(g)
// Draw an oval that fills the window
int x 0 int y 0
int width getSize().width-1
int height getSize().height-1
g.drawOval(x, y, width,
height)
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Create conten pane

• public JPanel createContentPane ()
• //Create and set up the content pane.
• ContentPanel new JPanel()
• ContentPanel.setLayout(null)
• SubmitButton new JButton("Square!")
• SubmitButton.setLocation(5, 220)
• SubmitButton.setSize(100, 30)
• SubmitButton.addActionListener(this)
• ContentPanel.add(SubmitButton)

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Create conten pane
ClearButton new JButton("Clear...")
ClearButton.setLocation(5, 280)
ClearButton.setSize(100, 30)
ClearButton.addActionListener(this)
ContentPanel.add(ClearButton)
// Insert Textfields XField new
JTextField(3) XField.setLocation(5,
30) XField.setSize(100, 30)
ContentPanel.add(XField)
ContentPanel.setOpaque(true)
return ContentPanel
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Process button click

• public void actionPerformed(ActionEvent e)
• if(e.getSource()SubmitButton)
• //get the data from the text fields
• Integer x
• x Integer.parseInt(XField.getText().t
  rim())
• Integer z
• zxx
• XField.setText(z.toString())
• else if(e.getSource()ClearButton)
• //clean the fields
• XField.setText("")

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Create and show GUI

• private static void createAndShowGUI()
• //This is to turn on the Default 'Look
  and Feel'.
• JFrame.setDefaultLookAndFeelDecorated(true
  )
• Frame new JFrame ("Multiplicator!")
• ButtonEx demo new ButtonEx()
• Frame.setContentPane(demo.createContentPan
  e())
• Frame.setDefaultCloseOperation(JFrame.DISP
  OSE_ON_CLOSE)
• Frame.setSize(800,600)
• Frame.setVisible(true)

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Combine all

• import java.util.
• import javax.swing.
• import java.awt.event.ActionListener
• import java.awt.event.ActionEvent
• public class ButtonEx implements ActionListener
• static JTextField XField
• JButton SubmitButton, ClearButton
• JPanel ContentPanel
• static JFrame Frame
• public static void main(String args)
• createAndShowGUI()

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Read from file

• public int readFromFile()
• try
• fin new FileInputStream ("input.txt")
  
• BufferedReader reading new
  BufferedReader(new InputStreamReader(fin))
• String thisLine
• //while not the end of file
• while ((thisLine reading.readLine()) !
  null)
• counter
• //close the input file
• fin.close()
• catch (IOException e)
• System.err.println ("Unable to read
  from file")
• return -1
• finally

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Stream tokenizer

• One option to read file with entries delimited by
• a custom symbol (set of symbols) is to read line
• by line and use an object of class
• StringTokenizer to extract each entry.
• For details, check http//java.sun.com/j2se/1.4.2
  /docs/api/java/util/StringTokenizer.html

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Write to file

• public void writeToFile(int n)
• try
• BufferedWriter writtingnew
  BufferedWriter(new FileWriter("output.txt"))
• writting.write("Total number of
  strings in input file " n )
• writting.close()
• catch (IOException e)
• System.err.println ("Unable to write
  to file")
• finally
• System.out.println("This is a last
  action")

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Exercises

• For using in the projects draw an oval on a
  button click
• For your own interest make your java application
  look like usual OS application. Set your own
  icon for the application. Make application window
  appear in the center of the screen.
• These are optional, no grades involved.