A DESCRIPTION OF THE REQUEST :
Pattern inherits hashCode() and equals() from Object which makes it useless for all except identity comparisons.

Pattern's only unique "state" is its pattern String so hashCode()/equals() using only pattern() as data seems reasonable.

JUSTIFICATION :
classes containing Pattern[] and Collection<Pattern> have to unpackage and perform pat.pattern().hashCode()/pat.pattern().equals(otherpat.pattern()) when implementing their own hashCode() and equals() methods. this is because hashCode() of all Collection<Pattern> subclasses use the hashCode() of the elements to generate its own hashCode value as does Arrays.hashCode(Pattern[]).

if Pattern implemented hashCode() at least one could use Arrays.hashCode(patArray) and Arrays.hashCode(col.toArray()) (for non-order-agnostic comparisons - sorting would have to be added to make such comparisons order-agnostic).


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
i would like to be able to compare and hash collections and arrays of Pattern without having to constantly extract its pattern() value.
ACTUAL -
Pattern.equals() only returns true for (this == other); ditto for hashCode(). this is no better than == alone (which could be useful if Pattern.compile() cached its results so that Pattern.compile("foo") == Pattern.compile("foo"), but that's a different matter).

---------- BEGIN SOURCE ----------

    public void testPattern() {
        Pattern pat1 = Pattern.compile("foo"), pat2 = Pattern.compile("foo");
        assertTrue("hashCodes don't equal for equivalent objects", pat1.hashCode() == pat2.hashCode());
        assertTrue("equivalent objects aren't equal", pat1.equals(pat2));
        assertTrue("sets of equivalent objects aren't equal", Sets.newHashSet(pat1).hashCode() == Sets.newHashSet(pat2).hashCode());
        assertEquals("sets of equivalent objects don't have identical hashCodes", Sets.newHashSet(pat1), Sets.newHashSet(pat2));
        assertTrue("arrays of equivalent objects aren't equal", Arrays.equals(new Pattern[]{pat1},new Pattern[]{pat2}));
        assertEquals("arrays of equivalent objects don't have identical hashCodes", Arrays.hashCode(new Pattern[]{pat1}),Arrays.hashCode(new Pattern[]{pat2}));
    }

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
I currently use a utility class (HashEqualsHelper) to centralize the unpackaging of pattern() from every Pattern when calculating hashCode and equals to ensure it's consistent system-wide. but for Collection<Pattern> implemented as:
public static int<T> hashCode(Collection<Pattern> col)
i'm stuck so all calling code must unpackage their collections into Pattern[] to call
public static int hashCode(Pattern[] array)
to compare pattern() to pattern().