©TheMcGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 6: Odds and Ends  Formatted Output  Random numbers

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Recall the Carpet Pricing Example  The price table for carpets ranging in size from 11 x 5 to 20 x 25 ft. whose unit price is $15 per sq. ft.  The outer for statement ranges from the first row (width = 11) to the last row (width = 20).  For each repetition of the outer for, the inner for statement is executed, which ranges from the first column (length = 5) to the fifth (length = 25).

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Output is a Table  But the numbers don't line up properly

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Formatting Output  To align values with varying numbers of digits, we must vary the number of spaces in front of the values.  The idea behind formatted output is to allocate the same amount of space for the output values and align the values within the allocated space.  We call the space occupied by an output value the field. The number of characters allocated to a field is the field width.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aligning Columns of Numbers  How to place a varying number of spaces to align the output values. Hyphen is used here to indicate the blank space.  One approach to determine how many spaces each number takes up and then pad with spaces to make it the the desired width.  Better to use the Formatter class from Java 1.5.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Formatter class  A Formatter is created with a PrintStream. Formatter fmt = new Formatter( System.out);  The format method is used with a format string that tells how to position the output values. fmt.format( "%8d", price); The format string is kind of like the 'picture' we used for DecimalFormat and DateFormat objects.  Formatter is in the java.util package.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The format method  The format method is what we call a variatic method It can take a variable number of arguments (one or more) There must be a format string The format string must contain a picture for each of the other arguments The format string can contain text that will also show up in the output

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Format Codes  % starts the picture for a value  The number after the % is the field width  The letter at the end is the type of the output value d => int s => String f => double in this case the number looks like x.y where the x is the total field width and the y is the number of digits after the decimal point

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Some Examples Formatter formatter = new Formatter( System.out); int num1 = 34, num2 = 9, num3; num3 = num1 + num2; formatter.format( "%3d + %3d = %5d\n", num1, num2, num3); String name = "John"; formatter.format( "Hello, %s!\n", name); GregorianCalendar day = new GregorianCalendar( 1776, 6, 4) formatter.format( "%1$tB %1$te, %1$tY\n", day);

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Other format methods  The signature is the same as the one in the Formatter class  PrintStream has a format method System.out.format( formatString, varList);  String has a static format method that returns a String String result = String.format( formatString, varList);

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Example: Loan Tables  The goal of this exercise is to design a program that generates a loan table. The table will compare different monthly payments for a set loan amount, with varying loan periods in each column and different interest rates in each row.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Loan Tables  The start method can be expressed as tell the user what the program does; prompt the user "Do you want to generate a loan table?"; while (the user says YES) input the loan amount; generate the loan table; prompt the user "Do another loan table?";

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pseudocode  The start method was expressed in pseudocode.  Pseudocode is an informal language used to express an algorithm.  It is useful in clarifying the purpose or function of the program without being tied down to the syntactic rules of a particular programming language.  Also useful for describing algorithms that may be implemented in many different languages.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Loan Tables  Other methods in the program: describeProgram: tells the user what the program does if the user requests it. getLoanAmount: gets the loan amount from the user. generateLoanTable: generates the loan table.  To compute the monthly loan payment, reuse the Loan class defined in Chapter 4.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Random Number Generation  The method Math.random is called a pseudorandom number generator and returns a number of type double that is greater than or equal to 0.0 but less than 1.0.  The generated number is called a pseudorandom number because it is not truly random.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Random Integers  The number returned from the random method ranges from 0.0 up to (but not including) 1.0.  If we want to generate random integers, we must perform a conversion so the number will fall within the desired range.  Use the formula: Y = {X * (max – min + 1)} + min  where X is the number returned by random.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Random Integers  The formula expressed in Java: //assume correct values are assigned to //'max' and 'min' int randomNumber = (int) (Math.floor(Math.random() * (max-min+1)) + min);

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Random Number Example *Ch6TestRandomGenerator generates N random numbers between 1 and 4 to simulate the suit of a drawn card.  It keeps one counter for each suit, and increments the matching counter after a random number is generated.  At the end of the generation, it prints the ratio count/N.

©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Random Class  The Random class is part of the java.util package  It provides methods that generate pseudorandom numbers of various types float nextFloat() int nextInt() int nextInt(n) produces integer in range 0 to n-1