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null pointer exception

andrew cassato
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Joined: Nov 14, 2010
Posts: 37
I am trying to write a program that takes in data from a text file which is just a list of random integers. I have three classes, one for Fractions, one for sorting them and one to run everything.

Somehow all the data is getting lost in the array "A" and I am getting a null pointer exception in the Fractions class (which was given to us so there is nothing wrong with it) at the line 155.

Fractions Class

Sort Fractions Class

Test Class

Ralph Cook
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Joined: May 29, 2005
Posts: 479
Without trying to debug your program, see if this gives you enough clues to find the problem.

You say you have a null pointer exception on the line " int a = frac1.getNumerator();" that means that frac1 is null, and therefore the program cannot "dereference" it (that's what it is called when you use a period to access a method or other element inside an object). So you are passing a null into the compare method somehow. If you put a trace statement indicating where you are in the array, you could determine what elements are getting passed in.

Your selection sort does not look right, but I'm afraid it's too late at night for me to take it apart now. try debugging that on a 4- or 5-element array, and step through the different loops.

Rob Spoor

Joined: Oct 27, 2005
Posts: 20193

Please UseOneThreadPerQuestion:

Closing this one.

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