created 09/05/99; revised 06/12/00, 06/02/03, 06/15/08, 07/30/12

Chapter 29 Programming Exercises

You might find it useful to look at the chapter after this one for some of these exercises.

Exercise 1 — Name Echo

Write a program that asks for user's name and then writes it back with the first name as entered, and the second name all in capital letters. Assume that there are two names, and that they are separated by a single space character. Use the trim() method to remove possible leading spaces. 

C:\>java NameEcho
Enter your name: Sherlock Holmes

Sherlock HOLMES

C:\>

Look at the documentation of the String class and use these methods:

The program could be improved by testing if there were indeed more than one name. (Test that the value returned from indexOf() is greater than zero.) If not, merely echo the input.

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Exercise 2 — charAt()

Write a program where the user enters a string, and the program echos it to the monitor with one character per line: 

C:\>java LinePerChar
Enter a string:
Octopus

O
c
t
o
p
u
s

To do this you will need to use the following method from class String: 

char charAt( int inx )

This method returns the character that is at index inx of the String. Characters are indexed beginning at index 0.

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Exercise 3 — Title Applier

Write a program that asks for the user's name and then writes that name to the monitor with either "Ms." or "Mr." in front, depending if the name is for a female or male. Assume that the only female names are

and that the only male names are

All other names will be echoed without a title. The program continues looping until the user hits "enter" without first typing a name. 

C:\>java Title
Enter a name:
Amy Johnson
Ms. Amy Johnson

Enter a name:
Fred Smith
Mr. Fred Smith

Enter a name:
Zoltan Jones
Zoltan Jones

Enter a name:

C:\>

Hints: Use a Scanner to read user input. Uses a while loop that tests the length of the input line. Use startsWith() to test the names.

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Exercise 4 — Microwave Menu

Microwave ovens usually have a keypad and display where the user enters the time as a sequence of digits. For example, if the user enters "23" this means twenty-three seconds and is displayed as "0:23". If the user enters "123" this means one minute twenty-three seconds and is displayed as "1:23". If the user enters "1530" this means fifteen minutes thirty seconds and is displayed as "15:30."

Write a program that asks the user to enter the time as a sequence of digits and then displays the time as "minutes:seconds" as above. Assume that if two or fewer digits are entered that the digits represent seconds. In this case, display a zero before the colon. If three or more digits are entered, the last two represent seconds. 

  C:\>java Microwave
  Enter cook time-> 123
  Your time->  1:23
  
  C:\>

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Exercise 5 — Documentation Printer

Write a program that reads in lines and outputs only those lines that start with // . When a Java source file is used as input the program will echo lines that describe the program. 

C:\>java Stripper < Hello.java

// Hello World Program
// written by Elmer

// Here is the main method:

C:\>

Look at the chapter "File Input and Output" if it is not clear what the command line is doing.

Hints: use a Scanner and nextLine()for input. The while loop of the program uses hasNextLine() to decide if it should continue. (Or, you can scan in a line and test its length.)

Exercise 5 — Better Documentation Printer

Write a program that reads in a source file and outputs only some lines:

  1. Lines that start with "//" are output.
  2. Lines that start with "/*" are output.
  3. Lines that start with "*/" are output.
  4. All lines between those that start with "/*" and "*/" are output.

To do this, use a boolean variable that is set to true when /* is encountered and is set to false when */ is encountered. Output lines when the variable is true.

Note: This program has a major design flaw because in Java comments may start with /* anywhere in a line and may end with */ anywhere in a line. Our program (as described) will miss these situations.

A better program outputs comments no matter where they begin and end. If you decide to do this, study the String documentation for useful methods. indexOf() comined with substring()would be especially useful.

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Exercise 6 — Password Checker

Write a program that repeatedly asks the user for a proposed password until the user enters an acceptable password. When the user enters an acceptable password, the program writes a message and exits.

Acceptable passwords:

  1. Are at least 7 characters long.
  2. Contain both upper and lower case alphabetic characters.
  3. Contain at least 1 digit.

The logic of this program can be quite tricky. Hint: use toUpperCase(), toLowerCase, and equals(). You will also need nested ifs.

Here is a run of the program: 


C:\>java PasswordChecker
Enter your password:
snowflake
That password is not acceptable.

Enter your password:
SnowFlake
That password is not acceptable.

Enter your password:
snowflake47
That password is not acceptable.

Enter your password:
Snowflake47
Acceptable password.

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