1. CMT4001 -- Programming Software Applications
Java Data Types and Operators
Week 2
Dr. Xiaohong Gao
TP B107, ext. 2252

2. Contents To become familiar with Java applications
To become familiar with variables in Java
To become familiar with Java primitive’s data types
To become familiar with arithmetic operators

3. A Simple Program 1 // Fig. 2.1: Welcome1.java
2 // A first program in Java 3
public class Welcome1 {
public static void main( String args[]) {
System.out.println( "Welcome to Java Programming!" ); } }
Welcome to Java Programming!

4. A Simple Program: Printing a Line of Text
1 // Fig. 2.1: Welcome1.java
// indicates the remainder of the line is a comment
Comments are ignored by the compiler
Use comments to document and describe code
Can also use multiple line comments: /* ... */
/* This is a multiple
line comment. It can
be split over many lines */
Another line of comments that describes the program
Note: line numbers are not part of the program; they are added for
our reference

5. A Simple Program: Printing a Line of Text3
A blank line
Blank lines and spaces make a program more readable
Blank lines, spaces, and tabs are known as whitespace
characters, and are ignored by the compiler
public class Welcome1 {
Begin a class definition for class Welcome1
Every Java program has at least one user-defined class
class keyword immediately followed by class name
Keyword: words reserved for use by Java
Naming classes: capitalize every word
SampleClassName

6. A Simple Program: Printing a Line of Text
public class Welcome1 {
Name of class called identifier
Series of characters consisting of letters, digits, underscores ( _ ) and dollar signs ( $ )
Does not begin with a digit
Contains no spaces
Examples: Welcome1, $value, _value, button7
7button is invalid
Case sensitive (capitalization matters)
a1 and A1 are different
For now, use public keyword
Certain details are not important now - mimic programs,
full discussions will come later

7. A Simple Program: Printing a Line of Text
public class Welcome1 {
Saving files
File name is class name and .java extension
Welcome1.java
Left brace
Begins body of every class
Right brace ends definition (line 9)
public static void main( String args[] )
Part of every Java application
Applications begin executing at main
Parenthesis indicate main is a method
Java applications contain one or more methods

8. A Simple Program: Printing a Line of Text
5 public static void main( String args[] )
Exactly one method must be called main
Methods can perform tasks and return information
void means main returns no information
For now, mimic main's first line {
Left brace begins body of method definition
Ended by right brace

9. A Simple Program: Printing a Line of Text
System.out.println( "Welcome to Java
Programming!" );
Instructs computer to perform an action
Prints string of characters between double quotes
String - series characters inside double quotes
White spaces in strings are not ignored by compiler
System.out - standard output object
Allows java to print to command window (i.e., MS-DOS prompt)
Method System.out.println displays a line of text
Argument inside parenthesis
Entire line known as a statement
All statements must end with a semicolon ;

10. A Simple Program: Printing a Line of Text
8 }
Ends method definition }
Ends class definition
Some programmers add comments to keep track of ending braces
Lines 8 and 9 could be rewritten as:
8 } // end of the method main ()
9 } // end of class Welcome1
Remember that the compiler ignores comments

11. A Simple Program // Fig. 2.2: Welcome2.java
2 // Printing a line with multiple statements 3
public class Welcome2 {
public static void main( String args[]) {
System.out.print ( "Welcome to Java);
System.out.println(“Java programming”); }
System.out.print keeps the cursor on the
same line, so System.out.println continues
on the same line.

12. A Simple Program Line numbers 1-2: Comments 3: Blank
4: Begin class Welcome2
5: Method main
6: Begin main body
7: Method System.out.print
8: Method System.out.println
9: end main
10: end Welcome2

13. A Simple Program: Printing a Line of Text
Escape characters
Backslash ( \ )
Indicates that special characters are to be output
Backslash combined with a character makes an escape sequence
\n - newline
\t - tab
Usage
Can use in System.out.println or System.out.print to create new lines
System.out.println( "Welcome\nto\nJava\nProgramming!" );

14. A Simple Program: Printing a Line of Text
// Fig. 2.3: Welcome3.java
2 // Printing multiple lines with just
3 // a single statements 4
5 public class Welcome3 {
public static void main( String args[]) {
System.out.print (“Welcome\
\nto\nJava\nProgramming!”); }
11 }
Notice how a new line is output for
each \n escape sequence.
Welcome to
Java
Programming!

15. Variables A variable has three properties:
a memory location to store this value
the type of data stored in the memory location
the named used to refer to the memory location

16. Variables The general syntax for declaring variables is:
<data type> <variables>
where variables is a sequence of identifiers separated by commas.
Example: int x;
int y;
or int x,y;

17. Variables Variables Visual representation 45
Variable names correspond to locations in the computer's memory
Every variable has a name, a type, a size and a value
Whenever a new value is placed into a variable it replaces (and destroys) previous value
Reading variables from memory does not change them
Visual representation
number1 45

18. Data type There are six numerical data types in Java: byte – integer
short –integer
int – integer
long –integer
float – real
double - real
Example: int j, k, l;
float numberOne, numberTwo;
long bigInteger;
double bigNumber;

19. Java’s primitive data types
Size
Description
Integers
byte
8-bit
Byte-length integer
short
16-bit
Short integer
int
32-bit
Integer
64-bit
long
Long integer
Real Numbers
float
32-bit
Single-precision floating-point
double
64-bit
Double-precision floating-point
Other Types
char
16-bit Unicode character
A single character
boolean
true or false
A boolean value(true or false)

20. Variables Assignment statement <variable> = <expression>;
Examples:
firstNumber = 234;
sum = firstNumber+ secondNumber;
solution = x*x-2*x+1;

21. Variables The variables firstNumber and
int firstNumber,secondNumber;
after A
is executed
firstNumber = 234;
secondNumber = 87;
firstNumber
secondNumber
The variables firstNumber and
secondNumber are declared and set
in the memory

22. Variables Values are assigned to the variables firstNumber
int firstNumber,secondNumber;
after B
is executed
firstNumber = 234;
secondNumber = 87;
firstNumber
234 B
secondNumber 87
Values are assigned to the
variables firstNumber
and secondNumber

23. Quick Check Why are the following declarations all invalid?
int a, b, a;
float x, int;
float w, int x;
bigNumber double;

24. Another Java Application: Adding Integers
int number1; // first number to add
int number2; // second number to add
sum; // sum of number1 and number2
Declares variables number1, number2, and sum of type int
int can hold integer values (whole numbers): i.e., 0, -4, 97
Data types float and double can hold decimal numbers

25. Another Java Application: Adding Integers
// add the numbers
sum = number1 + number2;
Assignment statement
First calculates sum of number1 and number2 (right hand side)
Next, uses assignment operator = to assign result to variable sum
Read as: sum gets the value of number1 + number2

26. Another Java Application: Adding Integers
System.out.printl(“The sum is”+ sum);
"The sum is " + sum
Uses the operator + to "add" the string literal "The sum is" and sum
Allows concatenation of a String and another data type
Results in a new string
If sum contains 117, then "The sum is " + sum results in the new
string "The sum is 117"
Note the space in "The sum is "

27. Arithmetic Arithmetic calculations are used in most programs
Use * for multiplication and / for division, +, -
No operator for exponentiation
Integer division truncates remainder
7 / 5 evaluates to 1
Modulus operator % returns the remainder
7 % 5 evaluates to 2
Operator precedence
Some arithmetic operators act before others (i.e., multiplication before addition)
Use parenthesis when needed
Example: Find the average of three variables a, b and c
Do not use: a + b + c / 3
Use: (a + b + c ) / 3

28. Arithmetic

29. Decision Making: Equality and Relational Operators
< _
> =

30. Summary Java applications Variables in Java
Java primitive’s data types
Arithmetic operators