Generic Programming - Java Concepts - page 1058

. . .
}

Purpose:

To define a generic method that depends on type variables

As with generic classes, you cannot replace type variables with primitive types. The
generic print method can print arrays of any type except the eight primitive types.
For example, you cannot use the generic print method to print an array of type
int[] . That is not a major problem. Simply implement a print(int[] a)
method in addition to the generic print method.

S ELF C HECK

5. Exactly what does the generic print method print when you pass an
array of BankAccount objects containing two bank accounts with
zero balances?

6. Is the getFirst method of the Pair class a generic method?

17.4 Constraining Type Variables

It is often necessary to specify what types can be used in a generic class or method.
Consider a generic min method that finds the smallest element in an array list of
objects. How can you find the smallest element when you know nothing about the
element type? You need to have a mechanism for comparing array elements. One
solution is to require that the elements belong to a type that implements the
Comparable interface. In this situation, we need to constrain the type variable.

public static <E extends Comparable > E min(E[] a)
{
E smallest = a[0];
for (int i = 1; i < a.length; i++)
if (a[i].compareTo(smallest) < 0) smallest =
a[i];
return smallest;
}

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778

You can call min with a String[] array but not with a Rectangle[] arrayȌthe
String class implements Comparable , but Rectangle does not.