1. Introduction to Java Applications2
Introduction to Java Applications

2. 2.1 Introduction Java application programming Display messages
Obtain information from the user
Arithmetic calculations
Decision-making fundamentals

3. 2.2 First Program in Java: Printing a Line of Text
Application
Executes when you use the java command to launch the Java Virtual Machine (JVM)
Sample program
Displays a line of text
Illustrates several important Java language features

4. 2.2 First Program in Java: Printing a Line of Text (Cont.)
Comments start with: //
Comments ignored during program execution
Document and describe code
Provides code readability
Traditional comments: /* ... */
/* This is a traditional comment. It can be split over many lines */
Another line of comments
Note: line numbers not part of program, added for reference
// Fig. 2.1: Welcome1.java
// Text-printing program.

5. 2.2 First Program in Java: Printing a Line of Text (Cont.)
Blank line
Makes program more readable
Blank lines, spaces, and tabs are white-space characters
Ignored by compiler
Begins class declaration for class Welcome1
Every Java program has at least one user-defined class
Keyword: words reserved for use by Java
class keyword followed by class name
Naming classes: capitalize every word
SampleClassName 3
public class Welcome1

6. 2.2 First Program in Java: Printing a Line of Text (Cont.)
Java identifier
Series of characters consisting of letters, digits, underscores ( _ ) and dollar signs ( $ )
Does not begin with a digit, has no spaces
Examples: Welcome1, $value, _value, button7
7button is invalid
Java is case sensitive (capitalization matters)
a1 and A1 are different
In chapters 2 to 7, use public class
Certain details not important now
Mimic certain features, discussions later
public class Welcome1

7. 2.2 First Program in Java: Printing a Line of Text (Cont.)
Saving files
File name must be class name with .java extension
Welcome1.java
Left brace {
Begins body of every class
Right brace ends declarations (line 13)
public class Welcome1 {

8. 2.2 First Program in Java: Printing a Line of Text (Cont.)
Part of every Java application
Applications begin executing at main
Parentheses indicate main is a method (Ch. 3 and 6)
Java applications contain one or more methods
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 declaration
Ended by right brace } (line 11)
public static void main( String args[] ) {

9. 2.2 First Program in Java: Printing a Line of Text (Cont.)
Instructs computer to perform an action
Prints string of characters
String - series characters inside double quotes
White-spaces in strings are not ignored by compiler
System.out
Standard output object
Print to command window (i.e., MS-DOS prompt)
Method System.out.println
Displays line of text
This line known as a statement
Statements must end with semicolon ;
System.out.println( "Welcome to Java Programming!" );

10. 2.2 First Program in Java: Printing a Line of Text (Cont.)
Ends method declaration
Ends class declaration
Can add comments to keep track of ending braces
} // end method main
13 } // end class Welcome1

11. 2.3 Modifying Our First Java Program
Modifying programs
Welcome2.java (Fig. 2.3) produces same output as Welcome1.java (Fig. 2.1)
Using different code
Line 9 displays “Welcome to ” with cursor remaining on printed line
Line 10 displays “Java Programming! ” on same line with cursor on next line
System.out.print( "Welcome to " );
System.out.println( "Java Programming!" );

12. 2.3 Modifying Our First Java Program (Cont.)
Escape characters
Backslash ( \ )
Indicates special characters be output
Newline characters (\n)
Interpreted as “special characters” by methods System.out.print and System.out.println
Indicates cursor should be at the beginning of the next line
Welcome3.java (Fig. 2.4)
Line breaks at \n
System.out.println( "Welcome\nto\nJava\nProgramming!" );

13. Fig. 2.5 | Some common escape sequences.

14. 2.4 Displaying Text with printf
System.out.printf
New feature of J2SE 5.0
Displays formatted data
Format string
Fixed text
Format specifier – placeholder for a value
Format specifier %s – placeholder for a string
Other format specifiers
System.out.printf( "%s\n%s\n",
"Welcome to", "Java Programming!" );

15. Formatting Output with printf
Precise output formatting
Conversion specifications: flags, field widths, precisions, etc.
Can perform
rounding
aligning columns
right/left justification
inserting literal characters
exponential format
octal and hexadecimal format
fixed width and precision
date and time format

16. Formatting Output with printf (Cont.)
Format String
Describe the output format
Consist of fixed text and format specifier
Format specifier
Placeholder for a value
Specify the type of data to output
Begins with a percent sign (%) and is followed by a conversion character
E.g., %s, %d
Optional formatting information
Argument index, flags, field width, precision
Specified between % and conversion character

17. Printing Integers Integer Format
Whole number (no decimal point): 25, 0, -9
Positive, negative, or zero
Only minus sign prints by default (later we shall change this)
Format
printf( format-string, argument-list );
format-string
Describe the output format
argument-list
Contain the value corresponding to each format specifier

18. Integer conversion characters.
View demonstration program Fig
Note output of positive, negative numbers
Note octal (base 8) and hexadecimal (base 16) options

19. Printing Floating-Point Numbers
Have a decimal point (33.5)
Computerized scientific notation (exponential notation)
is x 10² in scientific
is e+02 in exponential (e stands for exponent)
use e or E
f – print floating point with at least one digit to left of decimal
g (or G) - prints in f or e (E)
Use exponential if the magnitude is less than 10-3, or greater than or equal to 107

20. Floating-point conversion characters.
View program using printf for floating point numbers, Figure 28.4

21. Printing Strings and Characters
Conversion character c and C
Require char
C displays the output in uppercase letters
Conversion character s and S
String
Object
Implicitly use object’s toString method
S displays the output in uppercase letters
View program demonstrating character conversion with printf, Fig. 28.5

22. Printing with Field Widths and Precisions
Size of field in which data is printed
If width larger than data, default right justified
If field width too small, increases to fit data
Minus sign uses one character position in field
Integer width inserted between % and conversion specifier
E.g., %4d – field width of 4
Can be used with all format specifiers except the line separator (%n)
View program demonstrating field width, Fig

23. Printing with Field Widths and Precisions
Meaning varies depending on data type
Floating point
Number of digits to appear after decimal (e or E and f)
Maximum number of significant digits (g or G)
Strings
Maximum number of characters to be written from string
Format
Use a dot (.) then precision number after %
e.g., %.3f
View program demonstrating precision, Fig

24. Printing with Field Widths and Precisions
Field width and precision
Can both be specified
%width.precision
%5.3f
Negative field width – left justified
Positive field width – right justified
Precision must be positive
Example:
printf( "%9.3f", );

25. 2.5 Another Java Application: Adding Integers
Program Fig to do keyboard input
Use Scanner to read two integers from user
Use printf to display sum of the two values
Use packages

26. 2.5 Another Java Application: Adding Integers (Cont.)
import declarations
Used by compiler to identify and locate classes used in Java programs
Tells compiler to load class Scanner from java.util package
Begins public class Addition
Recall that file name must be Addition.java
Lines 8-9: begins main
import java.util.Scanner; // program uses class Scanner
5 public class Addition
6 {

27. 2.5 Another Java Application: Adding Integers (Cont.)
Variable Declaration Statement
Variables
Location in memory that stores a value
Declare with name and type before use
Input is of type Scanner
Enables a program to read data for use
Variable name: any valid identifier
Declarations end with semicolons ;
Initialize variable in its declaration
Equal sign
Standard input object
System.in
// create Scanner to obtain input from command window
Scanner input = new Scanner( System.in );

28. 2.5 Another Java Application: Adding Integers (Cont.)
int number1; // first number to add
int number2; // second number to add
int sum; // second number to add
Declare variable number1, number2 and sum of type int
int holds integer values (whole numbers): i.e., 0, -4, 97
Types float and double can hold decimal numbers
Type char can hold a single character: i.e., x, $, \n, 7
int, float, double and char are primitive types
Can add comments to describe purpose of variables
Can declare multiple variables of the same type in one declaration
Use comma-separated list
int number1, // first number to add
number2, // second number to add
sum; // second number to add

29. 2.5 Another Java Application: Adding Integers (Cont.)
Message called a prompt - directs user to perform an action
Package java.lang
Result of call to nextInt given to number1 using assignment operator =
Assignment statement
= binary operator - takes two operands
Expression on right evaluated and assigned to variable on left
Read as: number1 gets the value of input.nextInt()
System.out.print( "Enter first integer: " ); // prompt
number1 = input.nextInt(); // read first number from user

30. 2.5 Another Java Application: Adding Integers (Cont.)
Similar to previous statement
Prompts the user to input the second integer
Assign variable number2 to second integer input
Assignment statement
Calculates sum of number1 and number2 (right hand side)
Uses assignment operator = to assign result to variable sum
Read as: sum gets the value of number1 + number2
number1 and number2 are operands
System.out.print( "Enter second integer: " ); // prompt
number2 = input.nextInt(); // read second number from user
sum = number1 + number2; // add numbers

31. 2.5 Another Java Application: Adding Integers (Cont.)
Use System.out.printf to display results
Format specifier %d
Placeholder for an int value
Calculations can also be performed inside printf
Parentheses around the expression number1 + number2 are not required
System.out.printf( "Sum is %d\n: " , sum ); // display sum
System.out.printf( "Sum is %d\n: " , ( number1 + number2 ) );

32. 2.6 Memory Concepts Variables
Every variable has a name, a type, a size and a value
Name corresponds to location in memory
When new value is placed into a variable, replaces (and destroys) previous value
Reading variables from memory does not change them

33. 2.7 Arithmetic Arithmetic calculations used in most programs Usage
* for multiplication
/ for division
% for remainder
+, -
Integer division truncates remainder
7 / 5 evaluates to 1
Remainder operator % returns the remainder
7 % 5 evaluates to 2

34. Fig. 2.11 | Arithmetic operators.

35. 2.7 Arithmetic (Cont.) 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

36. Fig. 2.12 | Precedence of arithmetic operators.

37. Operator Precedence Chart
Hierarchy of Java operators with the highest precedence shown first.
Expressions inside parentheses are evaluated first; nested parentheses are evaluated from the innermost parentheses to the outer.
Operators in the same row in the chart have equal precedence.
Operator
Type
Order of Evaluation
(   )   
[   ]     .
Parentheses
Array subscript
Member access
left to right
++   --
Prefix increment, decrement
right to left
++   
Postfix increment, decrement
Unary minus
*   /   %
Multiplicative
+   -
Additive
<   >   <=   >=
Relational
==   !=
Equality
&&
And || Or
?   :
Conditional
=   +=   -=    *=   /=   %=
Assignment