1. Designing a Program & the Java Programming Language
Mrs. Butera

2. 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.

3. Machine Language

4. Modern Programming Languages

5. Examples of Programming Languages
BASIC
FORTRAN
COBOL
Pascal C
C++
Java
JavaScript
Perl
Python
Ruby
Visual Basic

6. 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

7. 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

8. BEFORE you write the Program, you conceive:
The Algorithm
& sometimes a
Flowchart

9. The algorithm is conceived before the program is written.
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.

10. 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

11. Flowchart Symbols

12. Gross Pay Flowchart Start Input Hours Input Pay Per Hour Calculate
Output
Gross Pay
Start

13. 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

14. Program Enhancements White Space and Indentation – for readability
Comments – for maintenance purposes
/*comment area */
// entire line

15. 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

16. 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

17. 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); }

18. Some Java Vocabulary Type of Element Examples + - * /
Arithmetic operators
+ - * /
Assignment operator =
Numeric literals
Programmer defined variable name
name, pay_per_hour, gross_pay

19. Invalid Program Syntax
Answer = (F - 32) * / 9;
Answer = )F - 32 ( * 5 / 9;
Answer = F – 32) * 5 / 9;
Answer = (F - 32) * 5.0 / 9.0

20. 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

21. 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); }

22. 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); }

23. 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); }

24. Programs are made up of lines and statements.

25. 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); }

26. 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); }

27. 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); }

28. 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 ff )
syntax errors may be returned
java Payroll - executes the program

29. The Compiler and the Java Virtual Machine (JVM)

30. Integrated Development Environments (IDE)
Software package including:
Text Editor
Compiler
Debugger
Other utilities
Examples:
NetBeans
Eclipse
Komodo
WinDev

31. The Programming Process
Clearly define what the program is to do (requirements).
Visualize the program running on the computer.
Use design tools to create a model of the program (algorithm, flowchart).
Check the model for logical errors.

32. 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.