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Thread: Theory questions about Java

  1. #1
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    Default Theory questions about Java

    I've been reading my text book and I'm studying for an upcoming test and I have some questions. As you might notice my questions are pretty basic but that's because we're only beginning to cover this topic and therefore we won't have anything serious on inheritance on the test but it will be there mildly. Anyways, on to my questions (sorry if they're badly worded):

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    1) If a class is not abstract but it has an abstract method, is it true that it still CAN NOT be instantiated? Or do abstract methods only exist inside abstract classes?

    2) The purpose of an abstract METHOD is to make sure the subclass overrides the method but what's the purpose of an abstract CLASS? Is the purpose of an abstract CLASS to be able to store the abstract METHODS? (that is IF I am right in saying that abstract methods HAVE TO BE in abstract classes)

    3) Imagine I had an array called, and set up as, array[rows][columns]. Doing array.length would give me the length of the rows but is array[].length the way to get the length of the columns?

    -------------------------------

    Any input would be greatly appreciated!
    Thanks in advance!

    Savvycom software
    Last edited by susan12; July 23rd, 2012 at 03:49 AM.


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    Default Re: Theory questions about Java

    Quote Originally Posted by susan12 View Post
    1) If a class is not abstract but it has an abstract method, is it true that it still CAN NOT be instantiated? Or do abstract methods only exist inside abstract classes?
    The animal doesn't exist. If it has abstract methods, it must be an abstract class or interface.

    2) The purpose of an abstract METHOD is to make sure the subclass overrides the method but what's the purpose of an abstract CLASS? Is the purpose of an abstract CLASS to be able to store the abstract METHODS? (that is IF I am right in saying that abstract methods HAVE TO BE in abstract classes)
    Having the class be abstract forces you to extend the class, to create a concrete subclass before using it.

    3) Imagine I had an array called, and set up as, array[rows][columns]. Doing array.length would give me the length of the rows but is array[].length the way to get the length of the columns?
    No, you have to give the row number, i.e., array[0], because you can have ragged arrays with different length of each row.

    -------------------------------

    Any input would be greatly appreciated!
    Thanks in advance![/QUOTE]

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