Program 6

• Any questions?

System.in

• Does the opposite of System.out

Reading

• Lines of text

• Single words

• Integers

• Doubles

• Etc.

Practice Problem

• Write Java code to ask for a student’s exam score out of 100. Your program is then to match the exam score to a letter grade and print the grade to the screen. The letter grade is to be calculated as follows:

90 and above A80-89 B70-79 C60-69 Dbelow 60 F

Switch Practice

• A program is required to read a customer’s name, a purchase amount and a tax code. The tax has been validated and will be one of the following:

0 tax exempt (0%)1 state sales tax only (3%)2 federal and state sales tax (5%)3 special sales tax (7%)

The program must then compute the sales tax and the total amount due and print the customer’s name, purchase amount, sales tax and total amount due.

Sentinel-Controlled loops

Initialize variable to be tested

Test variable against sentinel value

- Process variable as needed

- Update variable to be tested

Practice

• Design and write a program that will prompt for, receive, and total a collection of payroll amounts entered by the user until a sentinel amount of -99 is entered. After the sentinel has been entered, display the total payroll amount on the screen.

Problem 3

• Write a program that sums a sequence of integers. Assume that the first integer read specifies the number of values remaining to be entered. Your program should read only one value at a time. A typical input sequence might be

5 100 200 300 400 500

Problem 4

• Write a program that finds the smallest of several integers. Assume that input will end when a sentinel value of –999 is read. Do not count –999 as one of the integers to consider.

Working with Files

• Input is very straightforward.

• We just connect our Scanner to a File object instead of System.in or a String

• Do have to deal with exceptions

• Often just declare that we throw the exceptions

throws Clause

• Just an announcement that a particular method may throw a particular exception

• Used to help the programmers that call the method

• (more on exceptions in chapter 11)

Writing Files

• Writer classes

• Each classes has a purpose– FileWriter – connects to a file– BufferedWriter – makes output more efficient– PrintWriter – lets you use print and println

Using the FileWriters

FileWriter fw = new FileWriter(fileName);

BufferedWriter bw = new BufferedWriter(fw);

PrintWriter out = new PrintWriter(bw);out.println(“the first line”);

Alternative

PrintWriter out =

new PrintWriter

(new BufferedWriter

(new FileWriter(fileName)));

out.println(“the first line”);

Notes

• Using files always potentially throws IOExceptions.

• Sometimes we can handle these gracefully.

• Sometimes we need to allow the program to report an error and end.

File Practice

• Write code to read a file of integers and write a new file with one integer per line of the new file.

File Practice

• The files input1.txt and input2.txt each contain a list of numbers of type int in ascending order. Write a program to create a new file, output.txt, that contains all of the numbers from both input files in sorted order. Use a function that will accept as parameters any two open input streams and an open output stream.

More File Practice

• Write a program to read a file of data about employee raises and create a file of notes to the employees about their raises. The data is stored in the file “a:\\newSal.txt” in the form:LastName, FirstName OldSal NewSalFor each line, write to “a:\\letters.txt” a note in the form:Dear FirstName LastName,You have received a raise of raisePercentage%. Your new salary is NewSal.Write 3 blank lines before each note and 3 blank lines followed by a line of dashes after each note.