Designing a Program & the Java Programming Language

aniseedsplashSoftware and s/w Development

Aug 15, 2012 (4 years and 4 months ago)

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Designing a Program

&

the Java Programming
Language



Mrs. Butera


What is a Program?

A program is a set of instructions a computer
follows in order to perform a task. A
programming language is a special language
used to write computer programs.



Machine Language

Modern Programming
Languages

Examples of Programming
Languages


BASIC


FORTRAN


COBOL


Pascal


C


C++


Java



JavaScript


Perl


Python


Ruby


Visual Basic

History of Java


Developed by Sun Microsystems in 1991


Goal
: Develop a language that could be
processed by all the devices it controlled


not dependent upon the processor each
with its own machine language

Used in:


Stand
-
alone applications


Applets for the Internet and devices

Security

Can Java applets corrupt your computer?


NO!


Web browsers run Java applets in a secure
environment within your computer's memory
and do not allow them to access any of your
computer's resources

BEFORE you write the Program,
you conceive:


The Algorithm

& sometimes a

Flowchart

What is an Algorithm?

The set of well
-
defined steps that
are given to the computer to
perform a task or solve a problem.


The algorithm is conceived before
the program is written.

Example: Gross Pay Algorithm


Display: “How many hours did you work?”


Allow user to input hours worked


store the number
in memory


Display: “How much do you get paid per hour?”


Allow user to input pay per hour and store the
number in memory


Calculate Gross pay = Hours_Worked x
Pay_Per_Hour


Display the Gross Pay


Flowchart Symbols


Gross Pay Flowchart

Start

Input Hours

Input Pay Per Hour

Calculate

Gross Pay

Output

Gross Pay

Start

What is a Program Made of?



Vocabulary



the set of all words and
symbols in the language.


Syntax



rules for combine words into
sentences or statements.


Semantics



define the rules for interpreting
the meaning of statements

Program Enhancements




White Space and Indentation



for
readability


Comments



for maintenance purposes


/*comment area */


// entire line

Sample First Java Program


“Hello World”

// This is the classic first Java program

class HelloWorld {


public static void main(String[] args) {


System.out.println("Hello World!");


}

}

Save As
:

HelloWorld
.java


Key Words/Reserved Words


Every programming language has reserved
words that cannot be used as variable
names


When you compile your program, an error
will be returned if you use a reserved word
incorrectly

Key Words/Reserved Words

public class

Payroll

{


public
static

void

main(String[] args)


{



Int

hours = 40;



double

grossPay, payRate = 25.0;



grossPay = hours * payRate;


System.out.println(“Your gross pay is $” + grossPay);


}

}

Some Java Vocabulary

Type of Element

Examples

Arithmetic operators

+
-

* /

Assignment operator

=

Numeric literals

5.73 9

Programmer defined
variable name

name, pay_per_hour,
gross_pay

Invalid Program Syntax


Answer = (F
-

32) * / 9;


Answer = )F
-

32 ( * 5 / 9;


Answer = F


32) * 5 / 9;


Answer = (F
-

32) * 5.0 / 9.0



Semantics

Defines the rules for interpreting the

meaning of statements

Answer = (F
-

32) * 5.0 / 9.0;

Means “go into the parentheses first,
subtract 32.0 from the variable quantity
indicated by F, then multiply the result
by 5.0, and finally divide the whole
thing by 9.0” & store result in the
variable (storage area) Answer


Programmer
-
Defined Names

Variable are the names of memory locations that may hold data.

public class Payroll

{


public static void main(String[] args)


{



Int
hours

= 40;



double
grossPay
,
payRate

= 25.0;



grossPay

=

hours

*
payRate
;


System.out.println(“Your gross pay is $” +
grossPay
);


}

}

Operators

public class Payroll

{


public static void main(String[] args)


{



Int hours
=

40;



double grossPay, payRate

=

25.0;



grossPay
=

hours
*

payRate;


System.out.println(“Your gross pay is $” + grossPay);


}

}

Syntax/Punctuation

Marks the end of a complete sentence/statement.

public class Payroll

{


public static void main(String[] args)


{



Int hours = 40
;



double grossPay, payRate = 25.0
;



grossPay = hours * payRate
;


System.out.println(“Your gross pay is $” + grossPay)
;


}

}

Lines and Statements

Programs are made up of lines and statements.

Lines

A line is just a single line as it appears in the body of a program.

public class Payroll

{


public static void main(String[] args)


{



Int hours = 40
;



double grossPay, payRate = 25.0
;



grossPay = hours * payRate
;


System.out.println(“Your gross pay is $” + grossPay)
;


}

}

Statements

A statement is a complete instruction that causes the computer to
perform some action.

public class Payroll

{


public static void main(String[] args)


{



Int hours = 40
;



double grossPay, payRate = 25.0
;



grossPay = hours * payRate
;


System.out.println(“Your gross pay is $” + grossPay)
;


}

}

Variables

A variable is a named storage location in the computer's memory.

public class Payroll

{


public static void main(String[] args)


{



Int
hours

= 40
;



double
grossPay, payRate

= 25.0
;



grossPay

=
hours

*
payRate
;


System.out.println(“Your gross pay is $” +
grossPay
)
;


}

}

The Compiler and the Java
Virtual Machine (JVM)


Source Code = the program is typed in a text
editor. Source file example:
Payroll.java


javac Payroll.java



compiles

the program
-
(converts source code to byte code


3b 00 8h 01
84 ff ......)


syntax errors may be returned


java Payroll

-

executes

the program

The Compiler and the Java
Virtual Machine (JVM)

Integrated Development
Environments (IDE)

Software package
including:


Text Editor


Compiler


Debugger


Other utilities

Examples:



NetBeans


Eclipse


Komodo


WinDev

The Programming Process


1.
Clearly define what the program is to do
(requirements).

2.
Visualize the program running on the
computer.

3.
Use design tools to create a model of the
program (algorithm, flowchart).

4.
Check the model for logical errors.


The Programming Process

continued:


5. Enter the code and compile it.

6. Correct any errors found during
compilation. Repeat steps 5 & 6 as many
times as necessary.

7. Run the program with test data for input
(valid & invalid data). Have someone else
test it.

8. Correct any runtime errors found while
running the program. Repeat steps 5 & 6 as
many times as necessary.

9. Validate the results of the program.