java.util.Pair

[Goktug Gokdogan]

I think an object oriented language like Java should not contain a class
where there are so many different candidate names for its fields. It's a
code smell for improper abstraction.
There are lots of classes that are structurally similar but they are defined
in different classes as they are abstractions for different things, like
Point and Size.
Similarly, IMHO, developers should be encouraged to define their own classes
with a proper abstraction, adding classes like Pair will discourage to do
so.

On Tue, Mar 30, 2010 at 4:34 PM, <joe.darcy at oracle.com> wrote:

>
>
> On 3/30/2010 10:54 AM, Kevin Bourrillion wrote:
>
>> Pair is only a partial, flawed solution to a special case (n=2) of a very
>> significant problem: the disproportionate complexity of creating value types
>> in Java.  I support addressing the underlying problem in Java 8, and not
>> littering the API with dead-end solutions like Pair.
>>
>
> While I have sympathy with that conclusion, there is the
> side-effect of littering many APIs with the flotsam of lots of different
> classes named "Pair."  My inclination would be to produce one adequate
> Pair class in the JDK to prevent the proliferation of yet more Pair classes
> in other code bases.
>
> I should know better than to take the bait, below is a first cut at
> java.util.Pair.
>
> -Joe
>
> package java.util;
>
> import java.util.Objects;
>
> /**
>  * An immutable pair of values.  The values may be null.  The values
>  * themselves may be mutable.
>  *
>  * @param <A> the type of the first element of the pair
>  * @param <B> the type of the second element of the pair
>  *
>  * @since 1.7
>  */
> public final class Pair<A, B> {
>    private final A a;
>    private final B b;
>
>    private Pair(A a, B b) {
>        this.a = a;
>        this.b = b;
>    }
>
>    /**
>     * Returns a pair whose elements are the first and second
>     * arguments, respectively.
>     * @return a pair constructed from the arguments
>     */
>    public static <C, D> Pair<C, D> valueOf(C c, D d) {
>        // Don't mandate new values.
>        return new Pair<C, D>(c, d);
>    }
>
>    /**
>     * Returns the value of the first element of the pair.
>     * @return the value of the first element of the pair
>     */
>    public A getA() {
>        return a;
>    }
>
>    /**
>     * Returns the value of the second element of the pair.
>     * @return the value of the second element of the pair
>     */
>    public B getB() {
>        return b;
>    }
>
>    /**
>     * TBD
>     */
>    @Override
>    public String toString() {
>        return "[" + Objects.toString(a) + ", " + Objects.toString(b) + "]";
>    }
>
>    /**
>     * TBD
>     */
>    @Override
>    public boolean equals(Object x) {
>        if (!(x instanceof Pair))
>            return false;
>        else {
>            Pair<?,?> that = (Pair<?,?>) x;
>            return
>                Objects.equals(this.a, that.a) &&
>                Objects.equals(this.b, that.b);
>        }
>    }
>
>    /**
>     * TBD
>     */
>    @Override
>    public int hashCode() {
>        return Objects.hash(a, b);
>    }
> }
>
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