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keep getting NullPointerException error

Sally Curtis
Greenhorn

Joined: Jan 10, 2004
Posts: 26
i keep getting the following error
java:146: cannot resolve symbol
symbol : constructor NullPointerException (int)
location: class java.lang.NullPointerException
throw new NullPointerException(answer);

and the method is


does anyone know why this error keeps coming?
Adrian Yan
Ranch Hand

Joined: Oct 02, 2000
Posts: 688
Because NullPointerException doesn't take int as an argument. Also, why are you throws a NullPointer anyway? you should create your own Exception in this case.
Sally Curtis
Greenhorn

Joined: Jan 10, 2004
Posts: 26
How do i make my own exception?
Stefan Wagner
Ranch Hand

Joined: Jun 02, 2003
Posts: 1923

Your own Exception is a class, derived from another class.
Have a look at Exception in the docs.
If you find an appropriate parent in the list of exceptions (this needs some experience), you may extend that specific Exception.
If you need this exception only in one class, you may make it an inner class.

But Joshua Bloch claims to favor Standardexceptions, where they fit.
So you could throw the NullpointerException that way:

But isn't a null-Pointer-Ex thrown anyway?
So why catch it?
You may catch it, to give a more informative message, so the user may learn for the next time.
But you can do better.
You may test for (length < 1), and have the input in a loop:

Conclusio:
If you can catch the exception, and solve the problem, solve it as early as possible.
If you can not solve it be informative about the semantic of the error.
Perhaps the user may solve it.
Use StandardExceptions where appropriate.


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