Generic Programming - Java Concepts - page 1061

you can use addAll to add a LinkedList<SavingsAccount> to a
LinkedList<BankAccount> .

To see a wildcard with a super bound, have another look at the min method of
the preceding section. Recall that Comparable is a generic interface; the type
parameter of the Comparable interface specifies the parameter type of the
compareTo method.

public interface Comparable<T>
{
int compareTo( T other)
}

Therefore, we might want to specify a type bound:

public static <E extends Comparable <E> > E min(E[]
a)

However, this bound is too restrictive. Suppose the BankAccount class
implements Comparable<BankAccount> . Then the subclass
SavingsAccount also implements Comparable<BankAccount> and not
Comparable<SavingsAccount> . If you want to use the min method with a
SavingsAccount array, then the type parameter of the Comparable interface
should be any supertype of the array element type:

public static <E extends Comparable< ? super E >> E
min(E[] a)

Here is an example of an unbounded wildcard. The Collections class defines a
method

public static void reverse(List<?> list)

You can think of that declaration as a shorthand for

public static <T> void reverse(List<T> list)

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17.5 Raw Types

The virtual machine that executes Java programs does not work with generic classes
or methods. Instead, it uses raw types, in which the type variables are replaced with