1. Chapter 2: Java Fundamentals cont’d
Lecture 4: Monday Sept 11, 2006

2. Outline 2.1 The Parts of a Java Program
2.2 The print and println Methods, and the Java Standard Class Library
2.3 Variables and Literals
2.4 Primitive Data Types
2.5 Arithmetic Operators
2.6 Combined Assignment Operators
2.7 Conversion Between Primitive Types
2.8 Creating Named Constants with final
2.9 The String Class
2.10 Scope
2.11 Comments
2.12 Programming Style
2.13 Reading Keyboard Input
2.14 Dialog Boxes
2.15 Common Errors to Avoid

3. Operator Precedence What is the result of: Polynomial = 1+2*3+ 6/2 -2;
Is it ?
(1+2)*3 + 6/(2-2)
1+(2*3) +(6/2)-2
(1+2)*3 + (6/2)-2

4. Precedence Rules Always evaluate * , / and % before + and –
Always negate before any calculations
*, / and % have same precedence
+ and – have same precedence
If equal precedence then evaluate from left to right except for negations where we evaluate from right to left

5. Precedence examples Polynomial = 1+2*3+ 6/2 – 2;
Polynomial has the value of =8
Polynomial = –1 + 5 – 2; // 2
Polynomial = –(–3) + –(–5); //8

6. Grouping with parentheses
You can use parentheses to force the evaluation of a formula
Examples:
x * ( y + z*z ) instead of x*y + z*z
x * ( y * ( z ) + 85 ) – 65
Average = (a +b +c ) /3;

7. The Math class
value = Math.pow( x,y); // now value holds x to the power of y
value = Math.sqrt( x); //now value holds the square root of x

8. Combined Assignment Operators+=
x += 1;
x = x + 1; –=
x –= 1;
x = x – 1; *=
x *= 1;
x = x * 1; /=
x /= 1;
x = x / 1; %=
x %= 1;
x = x % 1;

9. 2.7 Conversion between Primitive Data Types
Before a value is stored in a variable, Java checks the Data Type of the value and the variable
If the data types are compatible then Java performs the conversion automatically  No Error
If the data types are not compatible then Java issues an error.

10. 2.7 Conversion between Primitive Data Types
A widening conversion is the conversion of a small value to a larger one
A narrowing conversion is the conversion of a large value to a smaller one
double largest
float
long
int
short
byte smallest

11. Widening conversion Example 1: Example 2: double x; int y = 10; x = y;
int x;
short y =2;
x= y;

12. Narrowing Conversion
We have to perform casting i.e. the name of the smaller data type is put in parentheses in front of the value
Example:
int number;
double pi = 3.14;
number = (int) pi;

13. Cast operator Used to convert from one primitive data type to another
Must be used for narrowing conversions

14. Example: int pies = 10, people = 4; double piesPerPerson;
piesPerPerson = pies /people;
piesPerPerson =(double) pies/people;
piesPerPerson =pies/(double) people;
piesPerPerson=(double)(pies/people);
(double)(10/4) = (double)(2) = 2.0
because it is an integer division
10/4 = 2 because it is an integer division
10.0/4 = 2.5 because one of the numbers
is a double
10/4.0 = 2.5 because people is double

15. Mixed Integer Operations
The result of an arithmetic operation that involves only byte, short, or int variables is always an int even if both variables are of data type short or byte
Example:
short x =5, y =7;
short z = x+y; // this statement gives an error
short z = (short) ( x+y ); //correct

16. Mixed Integer Operations
If one of the operator’s operands is a double then the result of the operation is a double
If one of the operator’s operands is a float then the result of the operation is a float
If one of the operator’s operands is a long then the result of the operation is a long

17. Creating named constants with final
A named constant is a variable whose value is read-only and cannot be changed
To create a named constant add the word final to declaration
An initialization value is required when declaring a constant
Example:
final double INTEREST_RATE = 0.069;

18. More about named constants
When naming a constant, the variable name should be written in all uppercase characters.
Math.PI is a constant that holds the value of pi ( i.e …)
Math.PI is already declared and initialized so it ready to use. Example:
double area = Math.PI * radius * radius ;

19. The String class A String literal is any text enclosed in quotations
A String is the DataType of a variable that can store String literals
Example of a String variable:
String name = “CS 0007”;
System.out.println( name );

20. The String class
To determine how many letters are stored in a String variable (name) use name.length();
Example:
String mycourse = “CS 0007”;
int number = mycourse.length();

21. String methods charAt(index)
index is an integer and specifies the character position in the String
This method returns the character at the specified position
Example:
char letter;
String myText = “This is my Text”;
letter = myText.charAt(8);

22. T h i s m y e x t String methods myText.length returns 15
because there are 15 characters T h i s m y e x t 1 2 3 4 5 6 7 8 9 10 11 12 13 14
myText.charAt(8) returns m
because m is the letter at position 8

23. String methods toLowerCase()
This method returns a new String that has all of the characters of the original String but in lowercase
Example:
String bigName = “I am BIG!!”;
String smallName =
bigName.toLowerCase();
// now smallName holds “i am big!!”

24. String methods toUpperCase()
Same as toLowerCase() but it converts all the characters to uppercase
Example:
String smallName = “I am Big!!”;
String bigName =
smallName.toUpperCase();
// now bigName holds “I AM BIG!!”

25. Example: String message = "Java is Great Fun!";
String upper = message.toUpperCase();
String lower = message.toLowerCase();
char letter = message.charAt(2);
int stringSize = message.length();
System.out.println(message);
System.out.println(upper);
System.out.println(lower);
System.out.println(letter);
System.out.println(stringSize);

26. Scope
The variable scope is the part of the program that has access to it
public class Scope {
public static void main(String[] args)
System.out.println(value); // ERROR!
int value = 100; }

27. Scope public class Scope { public static void main(String[] args){
int number = 100;
System.out.println(number);
int number = 200; //ERROR }

28. Homework due Monday Sept 18
Do Exercise 2 in the programming challenges page 113
Print your code and submit it in class