RFR(s): JDK-8144952: add wildcards to the Map.ofEntries() method

[Chris Hegarty]

This looks good Stuart.

-Chris.

On 10 Dec 2015, at 00:22, Stuart Marks <stuart.marks at oracle.com> wrote:

> Hi all,
> 
> 
> Joe Darcy pointed out that API changes I pushed into jdk9-dev yesterday are missing wildcards from the Map.ofEntries() method. Please see this bug:
> 
>  https://bugs.openjdk.java.net/browse/JDK-8144952
> 
> The Map.ofEntries() method currently has the following declaration:
> 
>  static <K, V> Map<K, V> ofEntries(Entry<K, V>... entries)
> 
> it should be changed to
> 
>  static <K, V> Map<K, V> ofEntries(Entry<? extends K, ? extends V>... entries)
> 
> This doesn't make all that much difference in practice. For example, this works:
> 
>  Map<Number, Number> map1 = MapOfEntries(entry(1, 2.0), entry(3.0f, 4L));
> 
> However, this does not:
> 
>  Map.Entry<Integer,Double> e1 = Map.entry(1, 2.0);
>  Map.Entry<Float,Long> e2 = Map.entry(3.0f, 4L);
>  Map<Number,Number> map = Map.ofEntries(e1, e2);
> 
> After adding the wildcards, the latter example compiles fine. This is a pretty unusual case, but for maximum flexibility it's probably a good idea to add the wildcards anyway.
> 
> Please review the diff appended below.
> 
> Thanks,
> 
> s'marks
> 
> # HG changeset patch
> # User smarks
> # Date 1449706837 28800
> #      Wed Dec 09 16:20:37 2015 -0800
> # Node ID b6540a8b7ab064600fe49a8bc678ad96127090ca
> # Parent  7f644a5d554a67457f3dd535c4435643d3f65569
> 8144952: add wildcards to the Map.ofEntries() method
> Reviewed-by: XXX
> 
> diff -r 7f644a5d554a -r b6540a8b7ab0 src/java.base/share/classes/java/util/Map.java
> --- a/src/java.base/share/classes/java/util/Map.java	Wed Dec 09 15:27:21 2015 -0500
> +++ b/src/java.base/share/classes/java/util/Map.java	Wed Dec 09 16:20:37 2015 -0800
> @@ -1670,9 +1670,9 @@
>      */
>     @SafeVarargs
>     @SuppressWarnings("varargs")
> -    static <K, V> Map<K, V> ofEntries(Entry<K, V>... entries) {
> +    static <K, V> Map<K, V> ofEntries(Entry<? extends K, ? extends V>... entries) {
>         Map<K, V> map = new HashMap<>(entries.length * 4 / 3 + 1); // throws NPE if entries is null
> -        for (Entry<K, V> e : entries) {
> +        for (Entry<? extends K, ? extends V> e : entries) {
>             // next line throws NPE if e is null
>             map.put(Objects.requireNonNull(e.getKey()), Objects.requireNonNull(e.getValue()));
>         }
> diff -r 7f644a5d554a -r b6540a8b7ab0 test/java/util/Map/MapFactories.java
> --- a/test/java/util/Map/MapFactories.java	Wed Dec 09 15:27:21 2015 -0500
> +++ b/test/java/util/Map/MapFactories.java	Wed Dec 09 16:20:37 2015 -0800
> @@ -377,4 +377,13 @@
>         assertEquals(sie.toString(), kvh1.toString());
>     }
> 
> +    // compile-time test of wildcards
> +    @Test
> +    public void entryWildcardTests() {
> +        Map.Entry<Integer,Double> e1 = Map.entry(1, 2.0);
> +        Map.Entry<Float,Long> e2 = Map.entry(3.0f, 4L);
> +        Map<Number,Number> map = Map.ofEntries(e1, e2);
> +        assertEquals(map.size(), 2);
> +    }
> +
> }