1. Program Style Console Input and Output
This slide set was compiled from the Absolute Java textbook slides (Walter Savitch) and the professor’s own class materials.
CSS161: Fundamentals of Computing

2. Techniques of Program Style
Naming Constants
Spelling Conventions
Comments
Indenting
No redundant code (use of methods)
CSS161: Fundamentals of Computing

3. CSS161: Fundamentals of Computing
Naming Constants
Declare numbers as named constants:
Syntax
public static final Type Variable = Constant;
Examples
public static final int INCHES_PER_FOOT = 12;
public static final double RATE = 0.14;
Naming Convention:
Use all uppercase letters, and designate word boundaries with an underscore.
Advantages
Changing a value in one place if it must be modified
preventing a value from being changed inadvertently
CSS161: Fundamentals of Computing

4. CSS161: Fundamentals of Computing
Spelling Conventions
Class names start with an upper letter: FirstProgram
Variable, Object, and method names start with a lower letter: answer
Punctuation is indicated with an underscore for a constant, otherwise an upper letter: INCHES_PER_FOOT, FirstProgram
Identifiers are spelled out in full: ArrayIndexOutOfBoundsException
Boolean variables should be named with a statement that will be true when the value of the Boolean variable is true: isPositive, pressureOK
Methods tend to start with a verb: equals( ), remove( ), add( )
CSS161: Fundamentals of Computing

5. Comments and Indenting
A line comment begins with the symbols //
A block comment begins with the symbol pair /*, and ends with the symbol pair */
Javadoc creates an HTML file that documents a given java program with /** */
Indenting shows the level of nested structures.
Self-documenting means the clear structure of a given program with no necessity of // coments.
CSS161: Fundamentals of Computing

6. CSS161: Fundamentals of Computing
Example
CSS161: Fundamentals of Computing

7. CSS161: Fundamentals of Computing
More Example
/**
* Is a CSS161 example program to see javadoc demonstration. *
Munehiro Fukuda
01/01/07
1.0 */
public class Css161Example {
* Is the main function.
arguments passed to the main function.
nothing
public static void main( String[] args ) {
function( ); // function call }
* Repeats printing "Hello!" three times
public static void function( ) {
System.out.println( "Hello!" );
Javadoc formats these block comments in html.
Indenting to show the level of nested structure.
A line comment
(This example contributes nothing
to understanding, though.)
CSS161: Fundamentals of Computing

8. CSS161: Fundamentals of Computing
Practice
Reformat the following code according to the program style you have learned:
public class Circumference {
double radius 10.0;
public static void main( String[] args ) {
double circumference = 2 * * radius;
System.out.println( “Circumference of radius 10.0 is “
+ circumference ); }
CSS161: Fundamentals of Computing

9. CSS161: Fundamentals of Computing
System.out.println
Syntax
System.out.println( Item_1 + Item_2 + … + Last_item );
Items: quoted strings, variables, numbers, or almost any object, which are concatenated together with +.
A new line added automatically
Examples
System.out.println( “Welcome to Java.” );
System.out.println( “Elapsed time = “ + time + “seconds” );
CSS161: Fundamentals of Computing

10. CSS161: Fundamentals of Computing
System.out.printf
Syntax
System.out.printf( “…%X1[.Y1]z1 … %X2[.Y2]z2 …”,
primitive_data1, primitive_data2, …);
where:
X: a digit
Y: a digit added with f, e, and g specifier
Z: a specifier such as d, f, e, g, s, and c
Examples
double price = 19.8;
String name = “magic apple”;
System.out.printf( “$6.2f for each $s.%n”, price, name );
%n: a new line added manually if necessary
CSS161: Fundamentals of Computing

11. CSS161: Fundamentals of Computing
Format Specifiers
CSS161: Fundamentals of Computing

12. CSS161: Fundamentals of Computing
Example (1 or 3)
CSS161: Fundamentals of Computing

13. CSS161: Fundamentals of Computing
Example (2 of 3)
CSS161: Fundamentals of Computing

14. CSS161: Fundamentals of Computing
Example (3 of 3)
CSS161: Fundamentals of Computing

15. CSS161: Fundamentals of Computing
Self-Test Exercises
Work on P67’s Self-Test Exercises 5 ~ 7 with your neighboring classmate.
CSS161: Fundamentals of Computing

16. CSS161: Fundamentals of Computing
Scanner Class
Convert each keyboard input (delimited by whitespace) into an appropriate data type.
Whitespace: blank spaces, tabs, and line breaks
Instantiation
import java.util.Scanner;
Scanner keyboard = new Scanner( System.in );
Major methods
Convert an input into a byte, a short, an integer, a long, a float, a double, or a string data type.
nextByte( ); nextShort( ); nextInt( ); nextLong( );
nextFloat( ); nextDouble( ); next( );
Get an entire line
next( );
Check if the next input can be converted into a byte, a short, an integer, a long a float, a double or a string data type.
hasNextByte( ); hasNextShort( ); hasNextInt( ); hasNextLong( ); hasNextFloat( ); hasNextDouble( ); hasNext( );
Check if there is another line to get.
hasNextLine( );
CSS161: Fundamentals of Computing

17. CSS161: Fundamentals of Computing
Example (1 of 3)
CSS161: Fundamentals of Computing

18. CSS161: Fundamentals of Computing
Example (2 of 3)
CSS161: Fundamentals of Computing

19. CSS161: Fundamentals of Computing
Example (3 of 3)
CSS161: Fundamentals of Computing

20. Scanner.useDelimiter( )
Change the delimiter from whitespace to "##"
Scanner keyboard2 = new Scanner(System.in);
Keyboard2.useDelimiter("##");
String word1 = keyboard2.next( );
String word2 = keyboard2.next( );
Inputs
abc##xyz
Values assigned
word1: abc
Word2: xyz
CSS161: Fundamentals of Computing

21. Pitfall: Dealing with the Line Terminator, '\n'
Given the code,
Scanner keyboard = new Scanner(System.in);
int n = keyboard.nextInt();
String s1 = keyboard.nextLine();
String s2 = keyboard.nextLine();
and the input, 2
Heads are better than
1 head.
what are the values of n, s1, and s2? \n \n
An empty string “”
CSS161: Fundamentals of Computing

22. CSS161: Fundamentals of Computing
Programming Tips
Prompt for Input
Scanner keyboard = new Scanner( System.in );
System.out.println( “enter the first name” );
String first = keyboard.next( );
System.out.println( “enter the last name” );
String last = keyboard.next( );
Echo Input
System.out.print( “the full name is %s %s %n”, first, last );
CSS161: Fundamentals of Computing

23. CSS161: Fundamentals of Computing
Self-Test Exercises
Work on P86’s Self-Test Exercises 13 ~ 14.
Work on P87’s Self-Test Exercises 15 ~ 16.
CSS161: Fundamentals of Computing