Assignment 04


Create a simple converter program that converts an entered distance from feet to meters and also from meters to feet.

Textbook: 2.6; 10.1 - 10.3
New concepts: Input, Scanner; exception handling.


Ask the user to enter a distance. Read this in as a decimal number (double) using a Scanner. Then print what that distance would be if converted from feet to meters, as well as from meters to feet. Print each conversion, clearly labeled, one per line.

Conversion: 1 foot = 0.3048 meters

If the user enters something that is not a number, your program must catch the resulting InputMismatchException so that it does not crash. Instead, it should print a polite error message and then end (without printing any other output).

Therefore, your final output should look something like this. Note how I executed the program four separate times; the command prompts and java command are not part of the output of the program. The stuff in green here is the input I typed when prompted by the program.

sp10code mmenor$ java MmenorA04
Please enter a distance to convert: 2.5
2.5 feet = 0.762 meters
2.5 meters = 8.202099737532809 feet

sp10code mmenor$ java MmenorA04
Please enter a distance to convert: 12
12.0 feet = 3.6576000000000004 meters
12.0 meters = 39.37007874015748 feet

sp10code mmenor$ java MmenorA04
Please enter a distance to convert: 1
1.0 feet = 0.3048 meters
1.0 meters = 3.280839895013123 feet

sp10code mmenor$ java MmenorA04
Please enter a distance to convert: one hundred
You must enter a number (only).  Please try again.

What to Submit

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Grading [4 points]

1 - Compiles
Your program compiles successfully (no errors)
0.6 - Input
You prompt the user to enter a double, which you use to do the calculations.
1.4 - Output
Program displays the correct results of the two conversions. Conversions are printed one per line, with one number followed by an f and the other by a m. (So you can either spell the words out or use the abbreviations ft and m.)
1 - Exception handling
Your program does not crash but instead prints an error message (and nothing else) on string input.


Where's the demo code from class?
Section 001:
What should my program do if the user enters a number and then a String? Do I need to report an error?
No. If the user enters a number, a space, and then something else, your program can just work with the number and ignore the rest. For example:
Please enter a distance to convert: 100 or so meters
100.0 feet = 30.48 meters
100.0 meters = 328.0839895013123 feet
Is it okay if my answer is very very close to the correct answer but not exactly the same?
Yes, that's fine. For example, you might get something like this (where the meters value has a trailing 000000001):
Please enter a distance to convert: 3048
3048.0 feet = 929.0304000000001 meters
3048.0 meters = 10000.0 feet

The reason for this is how doubles are stored internally. They are only precise to a certain number of decimal places and, depending on which math operations you perform on them and in which order, that last decimal place may get rounded a digit or two either way along the way. This is always a danger with double math that will become more obvious when we get to to the == (equality) operator next week.

There is a way to format floating point numbers when you print them, so you don't always have to have a big ugly string of digits. However, the formatting either involves the use of an object (such as an instance of java.text.DecimalFormat), or else a rather arcane formatting code (for example: System.out.printf("%.2f\n", feet)). Have a look at the textbook (section 3.6) if you're interested in these.