Download 081208

Final Review
James Atlas
August 12, 2008
“Family Feud” style
• Each team gets a chance to pick an answer
• The team with the highest ranked answer
gets to try to guess the rest
• 2 wrong answers and the other team can
then “steal” the category
• Each category winner gets candy!
• Must be able to explain a little about the
answer! And there are bonus questions…
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First, a list of topics
• http://www.cis.udel.edu/~atlas/cisc370/finalprep.html
• On the exam:
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Java basics
Syntax, primitive types, control flow, naming conventions
Basic OOP syntax, object-oriented design
OOP in Java: Inheritance, Interfaces, Polymorphism
Advanced classes: inner classes and anonymous classes
Packages
Exceptions
Java Input/Output
Serialization/Cloning
Java Collections framework
The Swing toolkit
Network programming
Multithreaded programming
Software design patterns
XML
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What is Java?
int
50 Object-oriented
float
30 Cross-platform
long
15 Large Library of Tools
Programming Language (Sun)
boolean
5
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Name some components of the Java
Virtual Machine
int
35 Bytecode Interpreter
float
30 Garbage Collector
long
25 Dynamic Compiler
boolean
10 Versions (native code for each platform)
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Name a Java primitive type
int
20 int
float
17 float
long
15 long
boolean
15 boolean
double
10 double
byte
10 byte
short
7
short
char
6
char
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Name a method/field access modifier
int
50 public
float
25 private
long
20 protected
boolean
5
package-private
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Name a different keyworded
method/field modifier
int
35 static
float
30 final
long
20 synchronized
boolean
10 volatile
double
5
transient
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How do you control a loop in Java?
int
50 for
float
25 while
long
10 do-while
boolean
10 break
double
5
continue
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What Java constructs provide the
basis for Object-oriented principles?
int
50 Classes
float
25 Interfaces
long
20 Abstract Classes
boolean
5
java.lang.Object/Instances
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BONUS: Every variable is passed-byvalue in Java, how does this work?
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What components/properties make
up a class definition?
int
25 Fields/variables
float
20 Constructors
long
15 Methods
boolean
15 Package
double
15 Imports
byte
10 Object hierarchy
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BONUS: What is overloading and how
is it handled in Java?
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Name some common Interfaces
related to the Java Collections
Framework
int
35 List
float
25 Map
long
20 Set
boolean
10 Collection
double
5
Comparable
byte
5
Queue
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What keywords are used in Java
Exception handling?
int
40 catch
float
30 try
long
20 throws
boolean
10 finally
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Name a Java I/O class or interface
int
30 InputStream
float
28 OutputStream
long
17 FileInputStream/Out
boolean
15 SocketInputStream/Out
double
6
DataInputStream/Out
byte
4
ObjectInputStream/Out
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BONUS: What design pattern does
Java I/O follow?
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Name a way/reason to use an innerclass
int
30 Hidden from other classes
float
26 Convenient
long
24 Implement interfaces on-the-fly
boolean
20 Access the surrounding implementation
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Name a general software pattern
(only ones we talked about in class)
int
35 Factory
float
30 Decorator
long
25 MVC
boolean
6
Command
double
4
Observer/Event
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Name a component of the Java Swing
framework
int
30 Frame
float
25 Container
long
15 Layout
boolean
10 Button
double
10 Panel
byte
6
Menu
short
4
Event
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Name a component of the Java
Network Programming model
int
60 Socket
float
25 ServerSocket
long
15 Stream
boolean
5
InetAddress
double
5
DatagramPacket
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Name an activity that a Java program
can perform on XML
int
35 parse/read
float
30 generate/write
long
25 transform
boolean
10 validate
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BONUS: Explain the difference
between the SAX and DOM
programming models
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The End!
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Object Destructors
• In C++ (and many other OOP languages),
classes have explicit destructor methods that
run when an object is no longer used.
• Java does not support destructors, as it
provides automatic garbage collection
 Watches/waits until there are no references to
an object
 Reclaims the memory allocated for the object
that is no longer used
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finalize()
• Java supports a method named finalize().
• method is called before the garbage collector
sweeps away the object and reclaims the
memory
• This method should not be used for
reclaiming any resources
 the timing when this method is called is not
deterministic or consistent
 only know it will run sometime before garbage
collection
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Summary of Inheritance
• Place common operations & fields in the
superclass.
 Remove repetitive code by modeling the “is-a”
hierarchy
 Move “common denominator” code up the
inheritance chain
• Protected fields are generally not a good
idea.
• Don’t use inheritance unless all inherited
methods make sense
• Use polymorphism.
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Abstract Classes
• Some methods defined, others not defined
• Classes in which not all methods are
implemented are abstract classes.
 public abstract class Animal
• Blank methods are labeled with the abstract
keyword also
 public abstract void feed();
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Abstract Classes
• An abstract class cannot be instantiated
• Subclass of an abstract class can only be
instantiated if it overrides each of the
abstract methods of its superclass and
provides implementation
 If subclass does not override all abstract
methods, it is also abstract
• Use abstract classes when you have a partial
implementation
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Methods: An Alternate Ending
• If a method throws an exception
 it does not return anything
 execution does not resume immediately
following the method call (as it would if the
method returns a normal value)
• JVM’s exception-handling mechanism
searches for an exception handler
 Exception handler: error recovery code
• runs to deal with a particular error condition.
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Streams
• Java handles input/output using streams
input stream: an object from which we can
read a sequence of bytes
Abstract class: InputStream
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Streams
• Java handles input/output using streams
output stream: an object to which we can write
a sequence of bytes
Abstract class: OutputStream
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Object Serialization
• Serialization: process of converting an object
to ordered data, to operate with streams
• To allow a class of objects to be written and read
with Object[Output/Input]Stream
 the class must implement the Serializable interface
• Serializable interface contains no methods
 “Marker interface”
 used to tag a class as able to be serialized
 refers to the class’s ability to be converted into a single
byte stream, which is then saved
• All classes are inherently serializable
 But you have to mark them as Serializable
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Object Serialization
• When an object is written to a stream, it is written
•
as a sequence of bytes.
Stores, in order
 fingerprinting information that describes the class
 instance fields and their values
 a more complete class description.
• The ability to convert an object from its “object”
state to a byte stream state is what makes the
direct writing and reading of objects possible
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Java-memory model (JMM)
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Java-memory model Rules
• Atomicity
 access/update to anything except long/double
• Visibility
 changes not always guaranteed visible
•
• synchronization does
• volatile variables
• Thread.join()
Ordering
 instructions in-thread are as-if-serial
 out-of-thread no guarantee
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Thread Synchronization
• In many multithreaded applications, more
than one thread will need to access the
same data
Can turn into a problem when two threads have
access to the same object and then both modify
the state of the object
Depending on the order of data access, the
object can become corrupted
Known as a race condition
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Synchronized Methods
• A method or block of code can be marked
as atomic
Using keyword synchronized in method’s
return type
After the section of code starts, the code is
guaranteed to complete before another thread
can enter another synchronized section
belonging to that same object
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Synchronization Diagram
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Wait/Notify Mechanism Diagram
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