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General Java Questions I
// row and col are int between (10..50) -- it's a big I know, but that
might not be the problem
My PROBLEM (and I don't know what to do, really), I can't access quad[x][y] outside
of the constructor!!!! Within the constructor I've got full access on quad[x][x]. Java
(1.2) returns a NullPointerException on any method except within the constructor!!!
What's my fault!???
Answer: I guess you shouldn't write Vector here:
Vector quad[][] = new Vector[row][col];
so, the correct variant may be:
quad[][] = new Vector[row][col];
I guess You just overridden your static variable with one defined in your constructor:
Vector quad[][].
Thus, you're initializing NOT your class-scope static variable but your
constructor-scope quad. It's not reachable outside the constructor. And as for static
quad, it has never been initialized! And a first reference to it causes
NullPointerException. I guess. I hope I'm right :)
--
Xao Rom
Q: I propose that Java should allow multiple inheritance if...
Everyone knows the potential problem with multiple inheritance is when you run into
the problem of having two instances of a grand parent super class.
For example:
class A extends D {int i; }
class B extends D {int i; }
class C extends A,B {}
Potentially, you could have two copies of D for each instance of C.
However, I propose that Java should allow multiple inheritance if there are no
instance variables associated with the abstracts that the base class is extending.
abstract class A { public setX(); public setY(); public setAll() {setX (); setY(); }
abstract class B { public setC(); public setD(); public setBoth()
{setC(); setD(); }
class C extends A,B {}
You won't have two instances of some grandfather class, since A and B doesn't have
instances variables.
I hope the next versions of Java explores this issue.
Answer: It does. They're called interfaces:
interface A { public void setX(); public void setY(); public void setAll(); }
interface B { public void setC(); public void setD(); public void setBoth(); }
interface C extends A,B {};
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