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Byron's CSC212 Web Site
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Class Notes
Wednesday August 30 , 2000
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Introduction to Programming in Java
Class Notes --
Wednesday August 30 , 2000
CSC212 - August 30, 2000
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Lecture Topic: INTRODUCTION TO PROGRAMMING
DEF: The "Computer" is a general purpose machine which
can be made to act like a special purpose machine
by means of a program.
A suggestive picture
__________
5 | The | 5,16,8,4,2,1
--------> |Collatz | ------------>
input stream |Program | output stream
|________|
__________
red,white,blue | | blue,red,white
-----------> | Sort | ------------->
input stream | Words | output stream
|________|
Remark
We want to write programs in Java to render the
computer a special purpose problem solver.
The approach we will adopt
We will write Java programs (text) by means of a
"template based slot and filler" scheme.
Basic application template
Write code which can be read & reused by others.
// Documentation - line
_
/* |
| Documentation - multiline
*/ _|
<?Class> Slot to fill in
<?Author> Programmer
Example: <?Class>.Java
HelloApp.java
<?Author> Byron Bahr
<?Line> Classical First Program
<?Program> IO.println("Hello World!")
Word
Java HelloApp.java
Java HelloApp
Hello World!
DEF: A Java Application Template is a test which is a
Java program except for "slots" which must be filled.+
These templates contain five textural sections:
1. General Information
2. Application Description
3. Required Packages
4. Program Section / Application Class
5. Demo
Remark: A concise way of presenting a program in class
is simply to display slots & fillers since most
of the other stuff is invariant technical
information.
A presentation of "Hello World" using slots & fillers:
<?Class> --> HelloApp
<?Author> --> My Name
<?Line> --> A Classical First Program
<?Description> --> ---------
---------
<?Needs> --> import IO.
<?Program> --> IO.Println ("Hello World!")
// Println = print & line feed
<?Demo> --> Hello World!
Remark: On the previous program, one can interpret
the line -
IO.println("Hello World!")
In the following way -
IO is an Object
Println("Hello World!") is a message.
Remark: The basic mechanism of computation of Object-
Oriented programming (OOP) is the sending of
messages to objects which respond with some
form of behavior.
Remark: In the sole executable instruction of the Hello
World program
The message println("Hello World!") is sent to
the object "IO" which responds behaviorly by
printing the string "Hello World!" to the
standard output file.
DEF: Object-Oriented Programming is a style of
programming which features the modeling of objects
in a hierarchical fashion and the sending of
messages to appropriately behaving objects.
DEF: A Message Send is a construct of the form -
<Object>.<Message>
which tells the computer to "send the message to
the object (which knows how to process it".
Hypothetical message sends:
Poker hand.display()
Money dime.area()
A Java program to read two integers display their sum:
<?Program> -->
// Read the two integers and store them in memory
// Declare Variable
int n1 = IO.read_int();
int n2 = IO.read_int();
// Compute the sum
int sum = n1 + n2:
// Display the Sum, Labeled
IO.print ("The Sum is: ");
IO.print (sum);
IO.println();
DEMO:
// Java Compiler
> javac SumOfTwoIntsApp.java
> java SumOfTwoIntsApp
12 Ret
7 Ret
The Sum Is: 19
Environment: Bindings in memory
n1 --> 12
n2 --> 7
sum --> 19
Message Sends:
5 in Program
2 obiedient
3 prints
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123456789112345678921234567893123456789412345678951234567
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