Program 6

1. Program 6 • Any questions?

2. System.in • Does the opposite of System.out

3. Reading • Lines of text • Single words • Integers • Doubles • Etc.

4. 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 A 80-89 B 70-79 C 60-69 D below 60 F

5. 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.

6. Sentinel-Controlled loops

7. 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.

8. 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

9. 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.

10. 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

11. 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)

12. 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

13. Using the FileWriters FileWriter fw = new FileWriter(fileName); BufferedWriter bw = new BufferedWriter(fw); PrintWriter out = new PrintWriter(bw); out.println(“the first line”);

14. Alternative PrintWriter out = new PrintWriter (new BufferedWriter (new FileWriter(fileName))); out.println(“the first line”);

15. 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.

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

17. 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.

18. 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.