Lab Exercise 2: Generating Syntax Errors

In this exercise you will make modifications to FirstApplet which will introduce syntax errors into your program. The main purpose here is to give you a first look at how your programming environment reports error messages. You'll also learn some of the most fundamental rules of Java syntax.

For each of the items below, make the editing change and then recompile the program. Make note of any error messages that are generated by the compiler. Try to understand what the message is telling you, and try to learn from the error, so it will be less likely to occur next time. After you have finished with that error, restore the code to its original form and move on to the next item.

• Java Language Rule. Every Java statement must end with a semicolon. Delete the semicolon at the end of one of the lines in the program. Repeat this experiment for different lines and note the error messages. Are they always the same? Sometimes the compiler can tell that you've forgotten a semicolon, but sometimes a missing semicolon causes the compiler to lose its place.

• Java Language Rule. Variables must be declared before they can be used. Turn the line in which the Button is declared into a comment by typing double slashes ``//'' at the beginning of the line. The compiler will now skip that line. Because you haven't removed the line from the source code, you can easily put it back in the program by removing the double slashes.

• Java Language Rule. Java names are case sensitive. Change the spelling of clickMe to ClickMe in the declaration statement but nowhere else in the program.