CS 9G Java Final Review

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CS 9G Java Final Review

• Welcome! My name is Jonathan Tsai
• Monday, December 13, 2004
• About 24 hours left until final
• Hope you enjoy the review session
• Slides will be available online at
• PowerPoint
• http//www.ocf.berkeley.edu/jontsai/files/cs9g_fi
  nal_review.ppt
• PDF
• http//www.ocf.berkeley.edu/jontsai/files/cs9g_fi
  nal_review.pdf

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CS 9G Java Final Review

• CS 9G Final (You should have already signed up)
• Tuesday, December 14
• 8-11am, 1230-330 or 5-8pm. All in the Bechtel
  Auditorium
• For updated info check http//www-inst.eecs.berke
  ley.edu/selfpace
• Worth 40 of your grade
• Need about 70 in class to pass (I'm not sure
  about this exactly)

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CS 9G Java Final Review

• What to expect on the final
• Big ideas in Java, topics indicated in the
  following slides
• Knowing exact parameters and names of functions
  in obscure methods that are rarely used is not
  important
• But having the proper syntax is
• Partial credit will be given for small errors
• Okay, ready? Let's go!
• If I go to fast, feel free to stop me and ask
  questions

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Adding Machine

• Applet
• import java.applet.Applet
• public void init ( )
• public void paint (Graphics)
• Widgets
• TextField
• Button
• Other
• public void actionPerformed(Event)

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Adding Machine

• Applet
• import java.applet.Applet
• public void init ( )
• public void paint (Graphics)
• Widgets
• TextField
• Button
• Other
• public void actionPerformed(Event)

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Adding Machine

• public void init( )
• Called whenever starting an applet
• HTML code
• ltapplet codeAddingMachine.class width300
  height200gtlt/appletgt
• Set up objects
• If have additional parameters to retrieve from
  HTML code to Applet
• Inside ltapplet ...gt and lt/appletgt, for each
  parameter put
• ltparam name"your_param_name" value"your_value"gt

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Adding Machine

• Applet
• import java.applet.Applet
• public void init ( )
• public void paint (Graphics)
• Widgets
• TextField
• Button
• Other
• public void actionPerformed(Event)

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Adding Machine

• public void paint(Graphics)
• Usually called by the applet whenever repaint( )
  is called
• Graphics object to be painted on must be passed
  in as a parameter
• Some Graphics method calls, given a Graphics
  object g
• g.drawString(Hello World)
• g.drawRect(0, 0, 50, 50)

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Adding Machine

• Applet
• import java.applet.Applet
• public void init ( )
• public void paint (Graphics)
• Widgets
• TextField
• Button
• Other
• public void actionPerformed(Event)

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Adding Machine

• Widgets
• import java.awt.
• import java.awt.event.
• Initialize it
• Button reset new Button(reset)
• Add it to the applet
• add(reset)
• Bind it with the actionListener
• reset.addActionListener(this)
• this refers to the current Applet

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Adding Machine

• Applet
• import java.applet.Applet
• public void init ( )
• public void paint (Graphics)
• Widgets
• TextField
• Button
• Other
• public void actionPerformed(Event)

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Adding Machine

• public void actionPerformed(Event)
• Determine the source of the Event e
• e.getSource( )
• Returns an object which corresponded to the call
  from the previous slide
• reset.addActionListener(this)
• Do some action
• Usually call repaint( ) as well

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Cat and Mouse
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Cat and Mouse

• Four Classes
• CatMouseChase.java
• Cat.java
• Mouse.java
• Position.java
• CatMouseChase was the Applet that controlled
  display and mouse interaction, etc

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Cat and Mouse

• Cat and Mouse represented the cat and mouse,
  respectively
• Each has a private field, Position, which
  represents the polar coordinates of the cat or
  mouse with respect to the base
• Create or instantiate a new object by calling the
  constructor
• Cat cat new Cat( )

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Cat and Mouse

• Use public accessor functions to retrieve the
  private fields
• Position catPos cat.getPosition( )
• Call public methods like so
• cat.move(0, 1)
• catPos.toString()

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Butterfly

• The classes
• ButterflyApplet
• ButterflyCollection
• Contains a data structure which holds butterflies
• Buttefly
• ButterflyDisplayer (for the thread, more on this
  later)
• Three versions
• Arrays
• Vector or LinkedList (using Java API)
• API Application Programming Interface
• Explicitly linked list (you made your own)

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Butterfly

• What was the point of this exercise?
• We hoped that you could see how you can implement
  your own data structure, such as a
  ButterflyCollection, that maintained a layer of
  abstraction between the applet/displayer and the
  actual butterflies being drawn
• Can use generic methods like add(Butterfly),
  remove(Butterfly), etc.

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Butterfly

• Implementing new data structures happens in real
  life all the time
• Usually performs specific additional features, or
  to optimize time/space
• Keep student records sorted by SID
• It's meaning is as simple as the name
• Something that holds data
• Can you think of data structures in real life (or
  Java) that is based on simpler data structures?

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Inventory

• The classes
• InventoryTest
• Instantiated a new Inventory object, and
  attempted to fill it
• Inventory
• Underlying data structure array of entries
• Entry
• The name of the item
• How many there are
• LineFormatException
• The different errors that occur in a badly
  formatted input file

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Inventory

• Let's examine some class and method signatures
• public Entry (String s) throws LineFormatException
  
• Yup, that's a constructor
• They can also support the throws keyword, just
  like any other method
• This simply means Calling this method can
  potentially cause this error (specifically, a
  LineFormatException).
• class LineFormatException extends Exception
• LineFormatException is a subclass of Exception
• This is a concept of inheritance, we'll get to
  that in a few slides

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Inventory

• When something bad happens, we'd like to throw an
  exception
• if (something_bad_happens)
• throw new LineFormatException(this is bad)
• Note that you don't just throw Exception, you
  have to throw new Exception
• Exceptions are just like any other object

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Inventory

• But don't fret! We have a safety net, which is
  part of the idea of exception handling
• try
• somethingBadMightHappen( )
• catch (LineFormatException e)
• // Display a message
• catch (Exception e)
• // this is in case an exception we didn't expect
  is thrown
• // consider it a safety net for the safety net
• // usually don't need to be this cautious

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Inventory

• So what's the deal with throws?
• We use this in a method signature to indicate
  that some caller to this method must implement
  try/catch, whether a direct caller or not
• Otherwise, the program will crash when the
  exception is encountered
• Example
• public void somethingBadMightHappen( ) throws
  LineFormatException
• throw new LineFormatException(just
  because)

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Bear
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Bear

• Depending how you implemented it, you might have
  4 classes (similar structure to Butterfly
  program)
• An applet
• Something that extends Frame
• A displayer
• The Bear
• We'll focus on the thread and application aspects
  of this program

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Bear

• A simple definition of an applet
• extends Applet
• has an init( ) method
• And an application
• has a main method
• Since we also want to have graphics displayed in
  a window, our application must also extend Frame
• This does not mean all applications have to
  extend Frame
• Inventory was an application that did not

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Bear

• Simple way to do it
• Put a main( ) method inside the applet that
  instantiated the class that extends Frame (we'll
  call it BearFrame)
• BearFrame has to also implements WindowListener,
  MouseListener
• We'll talk about interfaces and implements later

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Bear

• The thread aspect of the program
• So what?
• Computers and computer programs that we use
  commonly use don't really do multi-tasking
  (thought it seems that way)
• True multi-tasking would require a separate CPU
  for each process
• But, computers can achieve something to this
  effect by running multiple processes for a short
  interval at a time, and switching between them
  extremely rapidly
• These are called threads

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Bear

• How do I make a thread, say BearDisplayer?
• class BearDisplayer extends Thread
• public void run( )
• // This method is called by the program
  when
• // BearDisplayer.start( ) is called
• When do I use synchronized?
• Usually if the method is called inside the run(
  ), or is part of a resulting call by a method
  invoked in run( )
• Don't worry too much about the specifics, you'll
  learn more about this if you continue with CS

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Basics

• Naming convention
• Variables and Methods
• startWithLowerCase
• Initial letters of different words upper case in
  multi-word variable or method name
• If variable is final, all capitals, with
  underscore between words
• THIS_IS_A_CONSTANT
• Classes
• ThisIsAClass
• Like variable, first letter is upper-cased

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Basics

• Declare a variable
• int n
• Or many at a time int a, b, c, d
• Initialize a variable
• n 5
• Declare and initialize at same time
• int n 5
• int vars are initialized to 0 by default
• boolean to false
• But you shouldn't depend on this!
• If something is declare as final, you can't
  reassign it (constants like Math.PI)

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Basics

• Integer division
• int i 5
• i 5 / 2
• System.out.println(i)
• What gets printed out?

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Basics

• Only one public class per file
• I'll write a sample class module to demonstrate
  this
• Sorry for the spacing/indenting!
• File FinalExamReview.java
• public class FinalExamReview // note the name
• public FinalExamReview( ) // default
  constructor
• public void setName(String n) myName n
• public String getName( ) return myName
• public String toString( ) return myName
• public boolean equals(Object o) return
  false
• private String myName

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Basics

• Make a new FinalExamReview object
• FinalExamReview rev new FinalExamReview( )
• Do some stuff
• rev.setName(cs9g)
• System.out.println(rev)
• In the last example, rev is not a String, but
  it's toString method will be called by println to
  get it's String representation

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Basics

• Decisions if and switch
• if (just like C)
• if (something)
• else
• Can be nested
• if (something)
• else
• if (something_else)
• else

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Basics

• This block of statements
• if (something)
• else
• if (something_else)
• else
• Is equivalent to
• if (something)
• else if (something_else)
• else

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Basics

• Switch
• // generate a random integer between 0 and 10
• int n Math.random( ) 11
• String s
• switch (n)
• case 0
• s zero break // exit the switch
  statement
• case 1
• s one break
• default // if it did not match any previous case
• s greater than one // don't need break
  statement

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Basics

• Self test convert this code to not use switch
• // generate a random integer between 0 and 10
• int n Math.random( ) 11
• String s
• switch (n)
• case 0
• s zero break // exit the switch
  statement
• case 1
• s one break
• default // if it did not match any previous case
• s greater than one // don't need break
  statement

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Basics

• For loop
• for (int i0 i lt array.length i)
• // Do something
• While loop
• while (somethingIsTrue)
• // Do something

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Object Oriented Programming

• Why is OOP so cool?
• Reusable code
• How real world works (at least a good model of
  it)
• Public
• Private
• Static
• Inheritance
• Interfaces

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Object Oriented Programming

• Pronounced equals-equals (I do, at least)
• For objects
• Returns true if they are in the same memory
  location
• False otherwise
• For primitives like int, boolean
• Returns true if they have the same value
• False otherwise

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Object Oriented Programming

• public boolean equals(Object o)
• Pronounced dot equals (I do)
• If a class does not have one specified, the one
  that is implemented in Object will be used (since
  all classes extend Object implicitly)
• Note that it takes an Object as argument
• Can use instanceof operator
• I don't think you learned this but here's how
• if (o instanceof Butterfly)
• // o is indeed a Butterfly, cast it and use
  it
• else
• return false

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Object Oriented Programming

• public String toString( )
• Returns the string representation of an object
• If a class does not have one specified, the one
  that is implemented in Object will be used (since
  all classes extend Object implicitly), like
  equals
• Objects that are equals( ) to each other should
  have the same toString( ) representation

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Object Oriented Programming

• Why is OOP so cool?
• Reusable code
• How real world works (at least a good model of
  it)
• Public
• Private
• Static
• Inheritance
• Interfaces

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Object Oriented Programming

• Most methods are declared public
• Instance fields use with care!
• Usually only for constants
• Any method in any class will have access to it
• If the class was BankAccount and the field was
  balance, this would be highly undesirable for the
  bank (or highly desirable for you)

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Object Oriented Programming

• Why is OOP so cool?
• Reusable code
• How real world works (at least a good model of
  it)
• Public
• Private
• Static
• Inheritance
• Interfaces

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Object Oriented Programming

• Most instance fields are declared private
• Void methods, usually
• Methods of the same class can access these
• Note! This is not the same as saying that private
  fields are inaccessible from different objects
  (not to each other)

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Object Oriented Programming

• Why is OOP so cool?
• Reusable code
• How real world works (at least a good model of
  it)
• Public
• Private
• Static
• Inheritance
• Interfaces

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Object Oriented Programming

• Static means that there is only one copy of a
  method or field shared by all instances of that
  class
• Think of how one would keep track of the number
  of instances of a class ever created
• Static field numInstances will do
• How to invoke a static method
• ClassName.methodName(args)
• How to reference a static field
• ClassName.fieldName
• Public and private still apply

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Object Oriented Programming

• Why is OOP so cool?
• Reusable code
• How real world works (at least a good model of
  it)
• Public
• Private
• Static
• Inheritance
• Interfaces

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Object Oriented Programming

• Any class can only extend one class (no multiple
  inheritance like C)
• Protected
• Protected fields can be accessible in subclasses,
  but not by methods of classes outside of the
  inheritance hierarchy
• Cannot be protected and private
• Private fields are not inherited

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Object Oriented Programming

• Consider two classes
• class Parent
• protected hasTallGene true
• protected int height 0
• public void grow( )
• height
• if (hasTallGene)
• height

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Object Oriented Programming

• Consider two classes
• class Child extends Parent
• public void playCounterstrike()
• // play!
• And the declarations
• Parent p new Parent( )
• Child c new Child( )
• Parent p2 new Child( )
• Child c2 (Child) p

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Object Oriented Programming

• What would happen for the following statements?
• i.e. Is it normal behavior, runtime error, or
  compile time error?
• p.grow( )
• c.grow( )
• p2.grow( )
• c2.grow( )
• p.playCounterstrike( )
• c.playCounterstrike( )
• p2.playCounterstrike( )
• c2.playCounterstrike( )

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Object Oriented Programming

• Why is OOP so cool?
• Reusable code
• How real world works (at least a good model of
  it)
• Public
• Private
• Static
• Inheritance
• Interfaces

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Object Oriented Programming

• Interfaces
• Can have field declarations and initializations
• But not method bodies
• Implements keyword used in implementing classes
• Pretty obvious if you say it this way!
• Like a Java class, filename must be same as
  interface. Names usually end with -able
• File Sortable.java
• public interface Sortable
• public void sort( )
• private Object maxValue null

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Data Structures

• Data structures are good when they are general
• Though there is more code involved
• Consider a backpack vs. a laptop sleeve. Backpack
  is more versatile, can turn it into a laptop bag
  by throwing a sweater in it laptop sleeve can
  only hold a laptop

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Data Structures

• What is this extra work referring to?
• Remember what you put in the data structure
• What goes in is that which comes out
• Casting!
• Data structures usually store Object (general),
  but if you want to perform specific operations on
  those objects, they must be of the proper type
• Asking an Object that you expect to be a
  Butterfly for it's position will cause a
  compile-time error, because Object does not store
  a position

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Data Structures

• Operations you should be able to do
• Traverse it
• Search for something
• Convert it to another data structure (LinkedList
  to array, array to Vector, Vector to LinkedList,
  etc)
• Sort it (if you're up to the challenge)

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Data Structures

• Arrays
• All members are of the same type
• Fixed size
• Easy to use if you don't need to grow the
  collection
• Examples in Inventory, Butterfly
• int blah new int 6
• Each value is initialized to 0

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Data Structures

• Vectors
• Each member can be a different type (though not
  very useful)
• Instead, a Vector is a general purpose data
  structure
• Growable
• Remember to cast when retrieving
• How to traverse a Vector, convert it to other
  types

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Data Structures

• LinkedList
• Train analogy
• Be able to draw a box and pointer diagram
• Rearrange pointers
• Deleting nodes

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CS 9G Java Final Review

• Programming Assignments
• Applet Introduction Adding Machine
• Objects and Classes Cat and Mouse
• List Structures Butterfly
• Exception Handling Inventory
• Threads Bear
• Additional Topics
• Basic Java
• Object-oriented programming
• Data Structures
• Exceptions and Applications

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Exceptions

• See Inventory
• Common exceptions
• FileNotFoundException
• IOException
• ArrayIndexOutOfBoundsException
• Know these!

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Applications

• See Inventory
• Has main method
• public static void main (String args)
• Invoked by Java when running from the command
  line
• java InventoryTest inventory.data
• inventory.data is in the 0th position of args
• Review error handling in Inventory program
• Checking for files

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CS 9G Java Final Review

• You've made it through!
• The final won't be that hard if you could follow
  most of the review, so relax )
• Can email Carol at selfpace_at_cs.berkeley.edu if
  you really want to know your grade in a couple of
  days (will only tell you whether you passed the
  class). Otherwise, wait for it to be posted on
  BearFacts.

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CS 9G Java Final Review

• Good skill on the final!
• Don't forget to enjoy your break!

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