Hour 2: Writing Your First Program

NOTES AND CORRECTIONS

• If you're a Windows user having trouble with "Bad command or filename" errors or "Class not found" errors during this hour, read the online tutorial Using the Java Development Kit on a Windows System.

SOURCE FILES

• BigDebt.java (first version)
• BigDebt.class (first version)
• BigDebt.java (second version)
• BigDebt.class (second version)

READER QUESTIONS

• Question: When I save a file with Windows Notepad, it adds a .txt file extension to the filename, as in BigDebt.java.txt. How can I prevent this from happening?
  Answer: Put quote marks around the filename when you're saving it, as in "BigDebt.java". This prevents Notepad from adding the .txt file extension to the name. This problem does not occur under all Windows 95 configurations, but on those where it occurs, you won't be able to compile the program unless you rename it to take out the .txt file extension.
• Question: In MS-DOS, I seem to recall that there is a control key command to retype the previous line that you had typed in. Do you happen to know that command?
  Answer: After opening up an MS-DOS Prompt, enter the command doskey. This causes the commands you type in to be saved, and you can navigate backwards and forwards through these saved commands by using the up arrow and down arrow keys on your keyboard. This can be a timesaver as you're trying to fix a Java program that won't compile successfully.

ACTIVITIES

• Solution #1: BiggerDebt.java and BiggerDebt.class.
• Solution #2: Add errors to the BigDebt.java program and try to compile the program. Compare the error messages to the errors that you introduced in the program.