Whether you are just starting your first Java program, or you are a well
experienced programmer, your code can not be an error free code and
compile successfully from the first time. At the least you may confuse
variable names, forget to declare a variable, or miss a semicolon.
Java language errors, just like all other programming languages, can be
either syntax errors or logical errors. Syntax errors, also called
compile time errors, are illegal use of statements in terms of
programming language rules. When the compiler catches them it generates
an error message indicating the class name, line number where the error
is found, and the type of error. However, sometimes the actual error may
not actually be in the line indicated in the message. You would want to
look in and somewhere before these lines to locate the error.
This happens because syntax errors can be tricky sometimes; one error
may lead to more than one error message. A missing semicolon for example
causes the following one or more lines to be invalid, and thus
generates error messages for all of them. Once you fix that error, all
following messages will be cleared.
When writing a program with Java, syntax errors are almost unavoidable,
so do not panic or get disappointed when you encounter them. Some of
these errors are very common and you are very likely to encounter one or
more of them when compiling your code. The fact is, you cannot avoid
them. So the best way to deal with them is to get yourself familiar with
them and know how to fix them. Below are some of the most common errors
along with their solutions.
Capitalization Errors: Java language is case sensitive, variable names
must be exactly the same, Total is not the same as total and not the
same as toTal.
The file name is different than the public class name: The class should
be saved in a file with exactly the same name; a Shirt class should be
saved in a file named Shirt.java. Saving it to a different file name
will give a compiling error.
Javac cannot find the class: When you save your classes, or source
codes, they have to be in the very same directory where your javac.exe
is. This file is responsible for compiling your codes and is created
automatically when you download and successfully install the DSK
machine. Generally you would install the SDK into your C: drive so there
where your javac file will reside. Thus when saving your source code
you need to save it in the C: directory in a folder named java.
“javac is not recognized as an internal or external command, operable
program or batch file” (for Windows System) or “javac: Command not
found” (for UNIX System): This means that your compiler cannot find your
javac. This is due to one of two reasons, either you do not have a
javac at all because you did not install the correct machine, or you did
not set your PATH correctly. In this case you need to properly set your
PATH, or you will have to type in the full file name path to execute
it.
“Exception in thread “main” java.lang.NoClassFoundError: ‘fileName’: You
probably misspelled the fileName, remember that java is case sensitive.
“Line nn: ‘;’ expected”: This means you moved to a new line without
signaling to the compiler. When your string, or code line, is too long
to fit in one line, you may want to split into two lines. Doing that
just by pressing the Enter key will confuse the compiler and generate an
error. Instead you will need to concatenate with a ‘+’ sign. That is
split your string into two lines, ending the first with a ‘+’ before
moving to the second line.
