1. Introduction to Programming
Java Fundamentals (Numbers, Characters, Strings)
David Goldschmidt, Ph.D.
Computer Science
The College of Saint Rose

2. Common Programming Errors
Examples of programming pitfalls:
Don’t rush to writing code until you have sketched out an algorithm or solution
Create backups of your code using flash drives, etc.
Make sure every beginning has an end....
parentheses
public static int void main(String[] args) {
System.out.println("Quotes come in twos");
System.out.println("Answer: " + (9 + 5)); }
braces
quotes

3. Common Programming Errors
More examples of programming pitfalls:
Watch for misspelled Java keywords
Java is a case-sensitive language, so be careful of uppercase and lowercase letters
Don’t forget to end statements with a semicolon (;)
Or use { to open a new block of code
Watch for incompatible data types when you assign values to variables:
int x;
x = ;

4. Common Programming Errors
Even more examples of programming pitfalls:
Watch out for integer division:
Don’t use a variable unless it has been declared and assigned a value:
int result;
result = 1 / 2;
q = ;
int x;
System.out.println(x);

5. Representing Numeric Constants
Use the final keyword when you declare a variable to ensure its value cannot change:
Why use final?
final int monthsInYear = 12;
final double ourPI = ;
final double rate = ;
monthsInYear = 11; // ERROR!
rate = 0.07; // ERROR!

6. Formatting Numeric Output
When displaying floating-point numbers (i.e. data types float and double), you often want to format the output
e.g. instead of displaying $ , we would prefer to display $42.93
To do so:
Use the DecimalFormat class, which is part of the Java library
Create a DecimalFormat format pattern
Apply the pattern to the number to be formatted

7. Formatting Numeric Output
To use the DecimalFormat class, we first need to import the library via the import directive:
import java.text.DecimalFormat;
public class Name {
...

8. Formatting Numeric Output
Next, we create a DecimalFormat pattern by adding the following code to the main method:
Does formatting a number round the number?
double dollarAmt = ;
DecimalFormat df = new DecimalFormat( "0.00" );
System.out.print( "Cost is $" );
System.out.println( df.format( dollarAmt ) );

9. American Standard Code for Information Interchange
ASCII & Unicode Characters
Character data types are encoded as numbers
Java uses two bytes to store characters as Unicode
ASCII is the
American Standard Code
for Information Interchange

10. be enclosed in single quotes
Representing Characters in Java
Characters (e.g. letters, digits, symbols) are represented using the char data type
a character value must
be enclosed in single quotes
char c, d, e;
c = '4';
d = 'u';
e = '!';
System.out.print(c);
System.out.print(d);
System.out.print(e);
single character … single quotes
4u!
output

11. Character Strings A group of characters is called a character string
String literals are enclosed in double quotation marks:
The String class in Java allows you to create character string variables:
System.out.print( "This is a string" );
String s1 = "This is a string";

12. (i.e. create a String object)
Character Strings
In Java, String objects are similar to variables:
String s1 = "This is a string";
Declare variable s1
of type String
(i.e. create a String object)
Initialize variable s1

13. Character Strings
We can use print and println to display String objects in Java:
String firstName = "David";
String lastName = "Goldschmidt";
System.out.print( "Hello, " );
System.out.println( firstName );
System.out.print( "Bye Dr. " );
System.out.println( lastName );

14. The String Class & Methods
Once we have a String object created, we can use various methods of the String class
Determine the length of a String:
String firstName = "David";
String lastName = "Goldschmidt";
int len = lastName.length();
System.out.print( "Last name has " );
System.out.println( len + " letters." );

15. The String Class & Methods
Once we have a String object created, we can use various methods of the String class
Convert a String to uppercase or lowercase:
String s = "Java is so cool";
System.out.println( s.toUpperCase() );
String lower = s.toLowerCase();
System.out.println( lower );

16. The String Class & Methods
Once we have a String object created, we can use various methods of the String class
Obtain individual characters from the String:
Position (or index)
starts at zero
String s = "Java is so cool";
char firstLetter = s.charAt( 0 );
char thirdLetter = s.charAt( 2 );
System.out.print( firstLetter );
System.out.println( thirdLetter );

17. Reading Keyboard Input
A running Java program can have both output (System.out) and input (System.in):
System.out
System.in
Java Program
Execution

18. Reading Keyboard Input
To read input from the keyboard, we use Java’s Scanner class
Create a Scanner object associated with System.in:
Scanner keyboard = new Scanner( System.in );
Declare variable keyboard
of type Scanner
Create a Scanner object
and connect to System.in

19. Reading Keyboard Input
Once created, use the Scanner object to read keyboard input:
Scanner keyboard = new Scanner( System.in );
System.out.println( "What's your name?" );
String name = keyboard.nextLine();
System.out.println( "How old are you?" );
int age = keyboard.nextInt();

20. Reading Keyboard Input
To use the Scanner class, we need to import in the class from the java.util package:
import java.util.Scanner;
public class NameGame {
public static void main( String[] args )
...

21. Dialog Boxes Use a dialog box to display a message graphically:
import javax.swing.JOptionPane;
public class DialogBoxes {
public static void main( String[] args )
JOptionPane.showMessageDialog( null,
"This is called a dialog box." );