Request for Review : CR#8004015 : Add interface extends and defaults for basic functional interfaces

[Stephen Colebourne]

On 27 November 2012 02:12, Mike Duigou <mike.duigou at oracle.com> wrote:
> In the original patch which added the basic lambda functional interfaces, CR#8001634 [1], none of the interfaces extended other interfaces. The reason was primarily that the javac compiler did not, at the time that 8001634 was proposed, support extension methods. The compiler now supports adding of method defaults so this patch improves the functional interfaces by filing in the inheritance hierarchy.
>
> Adding the parent interfaces and default methods allows each functional interface to be used in more places. It is especially important for the functional interfaces which support primitive types, IntSupplier, IntFunction, IntUnaryOperator, IntBinaryOperator, etc. We expect that eventually standard implementations of these interfaces will be provided for functions like max, min, sum, etc. By extending the reference oriented functional interfaces such as Function, the primitive implementations can be used with the boxed primitive types along with the primitive types for which they are defined.
>
> The patch to add parent interfaces and default methods can be found here:
>
> http://cr.openjdk.java.net/~mduigou/8004015/0/webrev/
> http://cr.openjdk.java.net/~mduigou/8004015/0/specdiff/java/util/function/package-summary.html

Each of the default methods is formatted on a single line. I consider
this to be bad style, they should be formatted as per "normal"
methods:
@Override
public default Double operate(Double left, Double right) {
  return operateAsDouble((double) left, (double) right);
}

It is vitally important to get this kind of formatting/style correct.
Developers the world over will be copying what the style is in these
classes.

There is also no Javadoc on the default method override. In this case,
passing a null to either parameter will result in an NPE. This should
be documented.

More generally, you/Oracle should define a standard form of words for
describing what a default method does. Interfaces have not had them
before, and their behaviour needs documenting (even if it seems
obvious).

/**
 * An operation upon two operands yielding a result.
 * The operands and the result are all of the same type.
 * <p>
 * The default implementation calls {@link operate(double,double)},
 * throwing NullPointerException if either input is null.
 *
 * @param left  the first operand, not null
 * @param left  the first operand, not null
 * @return the result, not null
 */
@Override
public default Double operate(Double left, Double right) {
  return operateAsDouble((double) left, (double) right);
}

Stephen