1. Java Coding David Davenport Computer Eng. Dept.,
Syntax for Variables & Constants
Input, Output and Assignment a complete Java program
David Davenport
Computer Eng. Dept.,
Bilkent University Ankara - Turkey.

2. IMPORTANT… Students… Instructors…
This presentation is designed to be used in class as part of a guided discovery sequence. It is not self-explanatory! Please use it only for revision purposes after having taken the class. Simply flicking through the slides will teach you nothing. You must be actively thinking, doing and questioning to learn!
Instructors…
You are free to use this presentation in your classes and to make any modifications to it that you wish. All I ask is an saying where and when it is/was used. I would also appreciate any suggestions you may have for improving it.
thank you, David.

3. From problem to program…
The story so far...
Problem
Algorithm
Data/Memory requirements
Java Source Code
Java bytecode
Machine code

4. Need Java Syntax for… Algorithm (in pseudo-code)
Sequence, Decision & Repetition, of
Data flow operations
Input, Output & Assignment
Data/Memory requirements
Meaningfully named memory locations
Restriction on data (data types)
Variables or Constants & initial value
Plus comments & methods!

5. Comments & White space Comments Syntax:
// any text on remainder of current line
/* any text across multiple lines */
/** any text across multiple lines; a Javadoc comment! */
Examples:
Java ignores line endings, blanks lines & white space!
Use to automatically generate client API from source code.
// author: David. y = f(x); // computes…
/* This program blah, blah, blah */
Layout program code for ease of reading!

6. CS101 rule: Names must be meaningful!
Identifiers
User-defined names (for variables, constants, methods, etc.)
Any sequence of letters, digits and the underscore character only.
First character may not be a digit!
Upper and lower case are considered different
i.e. case sensitive!
Cannot use Java reserved words
i.e. words such as while, for, class, if, etc.
CS101 rule: Names must be meaningful!

7. Data Types For now, use only the following… Primitive Non-primitive
int (for numeric integer, e.g. 5, -27, 0, 510…)
double (for numeric real, e.g. 5.75, 3.0, -2.6…)
char (for any character, e.g. A, a, B, b, 3, ?, &, … )
boolean (for true / false only)
Non-primitive
String (for any sequence of zero or more characters e.g. “CS101”, “A”, “Well done!”, … )

8. Declaring Variables Syntax: Type Name (identifier) Examples:
Any Java type
Name (identifier)
Convention: first letter of embedded words capital, except first!
Examples:
int age; double area; double initialSpeed;
char letterGrade; char lettergrade;
String myName; boolean exists;
type name; 21
age
{int}
CAUTION
Java is case sensitive!

9. final type name = value;
Declaring Constants
Syntax:
Type
Any Java type
Name (identifier)
Convention: all capital letters (& underscore!)
Value (literal, variable, constant, expression)
Examples:
final int SPEEDOFLIGHT = 300;
final double PI = 3.142;
final String COMPANY = “Bilkent”;
final char LETTER_GRADE = ‘A’;
final type name = value;
Literal values
String use “…”
char use ‘.’

10. Output (1) Syntax: where output is
Literal value eg. “The area is ”, ‘?’, 12.5, …
Named variable or constant eg. area, userName, TAX_RATE, …
Expression eg. 2 * PI * radius, “The area is ” + area
System.out.println( output );
Value is output exactly as is!
Value in named memory location is output
Resulting value of expression is output
Note use of + for string concatenation

11. System.out.print( output );
Use
To output the value & leave text cursor on current line.
System.out.print( output );
System.out.println( “Welcome to CS101”);
System.out.println( “The tax rate is ” + TAXRATE + ‘%’);
System.out.println( “Goodbye.”);
System.out.println( “Welcome to CS101”);
System.out.print( “The tax rate is ”);
System.out.print( TAXRATE);
System.out.println( ‘%’);
System.out.println( “Goodbye.”);
System.out.println();
Start new line!

12. Outline Java Program The CS101 console template… ClassName.java
In Java
program = class
Classname
Convention: first letters capitalised
Filename & classname MUST be the same.
import java.util.Scanner;
/** …description…
@author …yourname…
@version 1.00, …date… */
public class ClassName {
public static void main( String[] args)
Scanner scan = new Scanner( System.in);
// constants
// variables
// program code }

13. Quick Demo…
Creating, compiling, running & debugging a Java program, using
the console & a text editor
an IDE (Integrated Development Environment)
JRE ~Java Runtime Environment
(the Java interpreter, java.exe, and libraries!)
JDK ~Java Development Kit
(the Java compiler, javac.exe, and other tools)

14. Syntax for Input and assignment statements.
More Syntax…

15. Input Syntax: Examples StringVariable = scan.next();
intVariable = scan.nextInt();
doubleVariable = scan.nextDouble();
userName = scan.next();
age = scan.nextInt();
salary = scan.nextDouble();
str = scan.nextLine();
Variables must be declared before use
Standard from Java5.0 on
Invalid input may give run-time error!
Program must include:
import java.util.Scanner;
Scanner scan = new Scanner( System.in);

16. Assignment Syntax: where expression is & resultVariable = expression;
… is assigned the result of …
Syntax:
where expression is
operand or
operand operator operand
&
Operand is
Literal value
Named Variable or constant
Result of method call
Expression (can use brackets to disambiguate)!
Operator is
+, -, *, /, % (modulus, remainder after integer division)
resultVariable = expression;
Result of expression must be of suitable type to put into resultVariable!

17. … is assigned the result of …
Assignment
… is assigned the result of …
Examples
What is the result of this?
Evaluation rules
Bracketed sub-expressions first
Operator precedence ( * / % before + - )
Left to right
total = 0; x = y;
sum = firstNumber + secondNumber;
netPay = grossPay * ( 1 – TAX_RATE/100);
count = count + 1;
c = Math.sqrt( a * a + b * b );
4 + 2 / 3 – 1

18. The complete Circle Computer program.
A complete example…

19. A Complete Example (1) Problem – find area & circumference… Algorithm
Data requirements
Print welcome message
Ask for & get radius from user
Compute area as pi.radius.radius
Compute circumference as 2.pi.radius
Report area, circumference & radius
L radius - int
L area, circumference - double
PI – double, constant = 3.142

20. The CS101 console template…
ClassName.java
import java.util.Scanner;
/** …description…
@author …yourname…
@version 1.00, …date… */
public class ClassName {
public static void main( String[] args)
Scanner scan = new Scanner( System.in);
// constants
// variables
// program code }
Again, start with the cs101 console template

21. The CS101 console template…
CirleComputer.java
import java.util.Scanner;
/** Report area & circumference of circle of radius given by user.
@author David
@version 1.00, 2019/10/17 */
public class CircleComputer {
public static void main( String[] args)
Scanner scan = new Scanner( System.in);
// constants
// variables
// program code }
Edit header comment…
change the ClassName
& save.

22. The CS101 console template…
CircleComputer.java :
public class CircleComputer {
public static void main( String[] args)
Scanner scan = new Scanner( System.in);
// constants
// variables
// program code
// 1. Print welcome message
// 2. Ask for & get radius from user
// 3. Compute area as pi.radius.radius
// 4. Compute circumference as 2.pi.radius
// 5. Report area, circumference & radius }
include algorithm steps as comments
& save again!

23. A Complete Example (3) CircleComputer.java
Header comment edited to include program description, author name & date.
import java.util.Scanner;
/**
* Report area & circumference of circle of radius given by user. *
David
1.00, 2017/10/07 */
public class CircleComputer {
public static void main( String[] args)
Scanner scan = new Scanner( System.in);
// constants
final double PI = 3.142;
// variables
int radius;
double area;
double circumference;
ClassName edited and file saved with .java extension.
& algorithm steps added as comments.
Include Java code for constants & variables

24. Put a blank line between logical sections
A Complete Example (3)
// 1. Print welcome message
System.out.println( "Welcome to Circle Computer.");
// 2. Ask for & get radius from user
System.out.print( "Please enter the radius: ");
radius = scan.nextInt();
// 3. Compute area as pi.radius.radius
area = PI * radius * radius;
// 4. Compute circumference as 2.pi.radius
circumference = 2 * PI * radius;
// 5. Report area, circumference & radius
System.out.print( "The area of a circle of radius ");
System.out.print( radius);
System.out.print( " is ");
System.out.println( area);
System.out.print( "and its circumference is ");
System.out.print( circumference);
System.out.println(); }
} // end class CircleComputer
add Java code for each algorithm step
Indentation
Put a blank line between logical sections
Note steps 2 & 5 expanded as per original algorithm.
Save…
Compile…
& Run!