Fundamentals of Computing: Program Style & Input/Output

Program StyleConsole 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

Techniques of Program Style • Naming Constants • Spelling Conventions • Comments • Indenting • No redundant code (use of methods) 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

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

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-documentingmeans the clear structure of a given program with no necessity of // coments. CSS161: Fundamentals of Computing

Example CSS161: Fundamentals of Computing

More Example /** * Is a CSS161 example program to see javadoc demonstration. * * @author Munehiro Fukuda * @since 01/01/07 * @version 1.0 */ public class Css161Example { /** * Is the main function. * * @param arguments passed to the main function. * @return nothing */ public static void main( String[] args ) { function( ); // function call } /** * Repeats printing "Hello!" three times */ public static void function( ) { System.out.println( "Hello!" ); System.out.println( "Hello!" ); 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

Practice public class Circumference { double radius 10.0; public static void main( String[] args ) { double circumference = 2 * 3.141592 * radius; System.out.println( “Circumference of radius 10.0 is “ + circumference ); } } • Reformat the following code according to the program style you have learned: 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

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

Format Specifiers CSS161: Fundamentals of Computing

Example (1 or 3) CSS161: Fundamentals of Computing

Example (2 of 3) CSS161: Fundamentals of Computing

Self-Test Exercises • Work on P67’s Self-Test Exercises 5 ~ 7 with your neighboring classmate. 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

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

\n \n \n \n An empty string “” 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? 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

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

Fundamentals of Computing: Program Style & Input/Output