Question

I am getting the following exception

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Java.CompileFile.doCompilation(CompileFile.java:48)
at GUI.CompilerForm.compileBtnActionPerformed(CompilerForm.java:225)
at GUI.CompilerForm.access$400(CompilerForm.java:23)
............

I no the error is at line 48 in CompileFile.java, it is saying that the array in NULL and i dont know why because that is where i am adding strings to it!

String[] compile;
int numberOfErrors = 0;
.
.
.
 for (Diagnostic diagnostic : diagnostics.getDiagnostics()) {                
            String errors = diagnostic.getKind().toString()+" on line  "+ diagnostic.getLineNumber() +"\nIn file:  \n"+ diagnostic.toString();
            compile[numberOfErrors] = errors;
            numberOfErrors++;
        }

I have tried System.out.println(errors); straight after i set it and it is working fine so i really dont know what is going on!

Any suggestions?

Answer 1

You’ve declared a variable called compile, but you haven’t shown anywhere that it’s given a value. Assuming it’s an instance variable, its value will default to null. You need to initialize it with:

compile = new String[someSize];

where someSize is “big enough”.

Alternatively, and preferrably, you could use a list:

// TODO: Rename variable to something more sensible
private final List<String> compile = new ArrayList<String>();

then…

compile.add(errors);

Then you can probably get rid of numberOfErrors too, as that would just be compile.size() presumably.