Download Java is a simple, object-oriented, distributed, interpreted, robust

Java Buzzwords
Java!

Java is a language characterized by buzzwords
– buzzword: A trendy word or phrase that is used more
to impress than explain
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From Sun Microsystems, the developers of Java:
“Java is a simple, object-oriented, distributed,
interpreted, robust, secure, architecture-neutral,
portable, high performance, multi-threaded, and
dynamic language.”

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.”

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.”
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.”
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.”

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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.”
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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.”
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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.”

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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, tamperfree 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.”
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.”
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.”

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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.”
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.”


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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
Decision Trees
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

Example tree structure
root 
depth of tree = 3
 edge
 leaf
 leaf
 leaf
 leaf
 leaf
 leaf
Decision trees

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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
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?
A Decision Tree
yes
yes
He received the
Physics Prize in 1921.
Would you like to
read about Einstein?
no
Try the Medicine
Prize in 1962.
Would you like to
read about a scientist?
yes
no
Look up the Peace
Prize in 1991.
Would you prefer
a humanitarian?
no
Try A. Solzhenitsyn,
Literature 1970.
A decision tree for sorting
a  b?
no
yes
b  c?
yes
a  c?
no
abc
yes
bac
a  c?
yes
acb
no
no
cab
b  c?
yes
bca
no
cba
Binary trees
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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?