Java Generics?

[keeler1]

I am writing a project for a class of mine and have run into a snag.

I have a parameterized class t


public class Polynomial<T extends Number>


Inside this class is a
Hashtable<Integer,T>

One method I have to make is one to take the derivative of the Polynomial, but not alter the original polynomial at all.

So I made a private constructor that takes a Hashtable


private Polynomial(Hashtable<Integer,T> newTable)

Inside my derivative method I create a new hashtable of the same type. So now I need to initialize it and call the private constructor

The derivative function looks like this so far


Hashtable<Integer,T> newTable = new Hashtable<Integer,T>();

Set<Integer> keySet = ht.keySet();

for(Integer key : keySet)
{
T newNum = ht.get(key);
Integer newKey = key - 1;


newTable.put(key -1, newNum.multiply(key));
}

the last line is killing me. newNum.multiply(key) returns a new Number (which is the parameterization of the entier class) but the compiler complains.

The error is


The method put(Integer, T) in the type Hashtable<Integer,T> is not applicable for the arguments (int, Number) Proj1/src/proj1 Polynomial.java line 53

So basically it doesnt like the return type of the method eventhough the entire class is parameterized to be of type <T extends Number>

Is there any way around this or any way to put constraints on the parameterization of the Hashtable?

[PaulFr]

Should that be:

1. public class Polynomial<T extends BigInteger> or
2. public class Polynomial<T extends BigDecimal>

(multiply() function are defined for these classes, is it defined for Number class) ?

[Quikee]

newNum.multiply(key) returns Number not T (multiply is not a generic function)...

a cast should solve this.

newTable.put(key -1, (T) newNum.multiply(key));


It might also be that boxing of "key -1" fails.

There might be other ways...