vectors and arrays

[ILtech]

"3. (5 points) Write a method for a class that uses an array

For the Vector class given below, write a method that computes the dot product of the Vector "this" object with the Vector object passed as an argument, "b". The dot-product is the sum of the products of the corresponding elements of the vectors. The Vectors must be the same length for the dot-product to be defined. For example, if a = {1,2,3,4} and b = {2,4,6,8}, the dot product would be 1*2 + 2*4 + 3*6 + 4*8 = 60.

      public class Vector {
         private double [] a;
         public Vector(double newData[]) {
            a=new double[newData.length];
            for (int i=0; i<newData.length; i++)
               a[i]=newData[i];
         }
         public int getLength() {
            return a.length;
         }
         public double getEntry(int index) {
            return a[index];
         }
         public double dotProduct(Vector b) {
         // YOUR CODE GOES HERE
         }
      }

"

So this is my assignment. The title suggests only using arrays and the constructor takes an array but the dotProduct method takes a vector as an argument. So, I'm assuming I'm supposed to convert vector b to an array or convert array a to a vector.

So, my question is this: How do I convert to one or the other? I've looked around for examples but they don't seem to make sense or translate very well into my situation. Help, please?

[Nepomuk]

...So, my question is this: How do I convert to one or the other?

Simple: You don't have to. You have a method called getEntry in there, so if you want to get an array from your vector, you can just create a new one with those entries. But you can just as well use the given Vector and use a.getEntry(i) instead of [i]a.

Greetings,
Nepomuk

[ILtech]

Uhm...kay?

The thing that's throwing me off is that my class hasn't said a word about vectors so I don't really know how to work with them.

If I wanted to make an array out of the vector in the dotProduct, how would I do that?

Something like...

double [] bArray = new double[b.size()] //the b.size() gives me an error...and i've imported java.util.* so what do i do here?
 
for (int i = 0; i < b.size(); i++) {
bArray[t] = b.getEntry(t);
}
 

:s Thank you for your help.

[Nepomuk]

Uhm...kay?

The thing that's throwing me off is that my class hasn't said a word about vectors so I don't really know how to work with them.

If I wanted to make an array out of the vector in the dotProduct, how would I do that?

Something like...

double [] bArray = new double[b.size()] //the b.size() gives me an error...and i've imported java.util.* so what do i do here?
 
for (int i = 0; i < b.size(); i++) {
bArray[t] = b.getEntry(t);
}
 

:s Thank you for your help.

OK, you seem to be confused - there IS a class Vector in the package java.util.*, but you have one defined yourself (see, it says public class Vector in your code), so you have to work with that. It doesn't have a method called size(), instead it's called getLength() or something like that.
Other than that, I think your code should be correct so far.

Greetings,
Nepomuk

[ILtech]

Thank you very much. I've got it all working now. :]

[Nepomuk]

Thank you very much. I've got it all working now. :]

You're welcome of course and I'm glad it's working now. :-)

Greetings,
Nepomuk