Lecture on object oriented programming.ppt

material

1. Java Buzzwords

2. Java!
Java is a language characterized by buzzwords
–buzzword: A trendy word or phrase that is used more
to impress than explain
From Sun Microsystems, the developers of Java:
What do all of those terms mean?
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

3. A programming language
–a vocabulary and set of syntactical (grammatical)
rules for instructing a computer to perform specific
tasks
–you can do most anything in any programming
language
–a particular language encourages one to do things
in a certain way
Question: Is this a fair characterization?
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

4. Based on popular languages called C and C++
C: old, pretty bare bones language
C++: newer, more complicated language
Start from C and add some of C++’s more useful
features
“Java omits many rarely used, poorly understood,
confusing features of C++ that in our experience
bring more grief than benefits” (Gosling)
Question: Is Java really all that simple?
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

5. The object-oriented paradigm
–problems and their solutions are packaged in
terms of classes
–the information in a class is the data
–the functionality in a class is the method
–a class provides the framework for building objects
Object-oriented programming (OOP) allows pieces of
programs to be used in other contexts more easily
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

6. A distributed system is one where multiple separate
computer systems are involved
–the Internet is a very large distributed system
•interconnected collection of computer networks
•heterogeneous components
•large number of services: WWW, file services,
audio/video channels
Java was designed for the web
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

7. Java a high-level language
High-level languages must be translated to a
computer’s native tongue, machine language
Interpreted high-level languages are translated to an
intermediate form and then converted to machine
language and run
–Java bytecodes
–bytecode (class) file is executed by a Java
bytecode interpreter
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

8. Programs will have errors, but a good program
degrades reasonably
A robust program may not do exactly what it is
supposed to do, but it should not bring down other
unrelated programs down with it
Reliability
–early (compile time) checking
–dynamic (runtime) checking
–eliminating situations that are error prone.
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

9. Security
–techniques that ensure that data stored on a
computer cannot be read or compromised
Java is intended for use in networked/distributed
environments
–a program is running on your computer … what is to
stop it from erasing all of your data, accidentally or
otherwise?
Java enables the construction of virus-free, tamper-free
systems
–authentication based on public-key encryption
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

10. A language is architecture-neutral if it does not prefer a
particular type of computer architectures
Example:
–not too hard to construct a program that will run faster
on a Macintosh than on a PC, and vice-versa
–each have their own respective strengths and
weaknesses
A particular program is never entirely architecture
neutral though
Question: When is being architecturally neutral a bad
thing?
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

11. Program once, run anywhere
A program is portable if it will work the same (more
or less) on many different computer systems
–platform-independent
Much effort is currently spent porting non-portable
code
Java has no "implementation dependent" aspects
HTML is also portable or platform-independent
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

12. Performance: speed in completing some task
–performance is everything to most computer and
software manufacturers!
Think about this …
–if the transportation industry kept up with the
computer industry, one would be able to now buy a
Rolls Royce that could drive across country in 5
minutes for $35
However …
–it would crash once a week, killing everyone on
board
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

13. A thread is a part of the program that can operate
independently of its other parts
Multi-threaded programs can do multiple things at
once
–example:
•download a file from the web while still looking
at other web pages
Question: What is the problem with multiple agents
working at the same time?
–synchronization
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

14. Dynamic: actions that take place at the moment they
are needed rather than in advance
–antonym: static
A dynamic program can
–ask for more or less resources as it runs
–use the most recent version of some code that is
available
Question: Why is being dynamic a good thing?
–upgrades
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

15. Decision Trees

16. Trees
Hierarchical data structure
Set of elements or nodes
–one node as root
–every other node has a single predecessor (parent)
and zero or more successors (children)
–nodes without successors are called leaf nodes
Nodes are connected by edges
The level or depth of a node is the number of edges on
the path to the root
The depth of the tree is the number of edges on the
longest path from root to any leaf
A complete tree has all leaves at same level, all other
nodes have the same number of children

17. Example tree structure
 leaf leaf leaf leaf leaf
root 
 leaf
depth of tree = 3
 edge

18. Decision trees
A decision tree begins with a decision you need to
make
–start with an initial decision node
–ask a question
Structure for investigating options and the possible
outcomes of choosing those options
–result of a decision can be another decision
–outcome is a terminal node
Tree should have unique paths from the decision node
to each of the terminal nodes.
–help you to choose between several courses of
action

19. Examples
Real life decision trees
–which route to take to class?
–which {cell phone, computer, camera} is
best for me?
–what to wear?
–where to go on vacation?

20. He received the
Physics Prize in 1921.
Try the Medicine
Prize in 1962.
Would you prefer
a humanitarian?
Would you like to
read about a scientist?
Would you like to
read about Einstein?
Try A. Solzhenitsyn,
Literature 1970.
Look up the Peace
Prize in 1991.
A Decision Tree
yes
yes
yes
no
no
no

21. A decision tree for sorting
yes
a  b?
b  c? a  c?
no
yes no
a  b  c
a  c?
a  c  bc  a  b
yes no
yes no
b  a  c
b  c?
b  c  ac  b  a
yes no

22. Binary trees
Nodes have at most two children
In a complete binary tree of depth 3,
–how many nodes are in the tree?
–how many leaves are in the tree?
In a complete binary tree of depth 4,
–how many nodes are in the tree?
–how many leaves are in the tree?
How many nodes in a depth d tree?
How many leaves in a depth d tree?