Well, that's a thorny issue... POJOs are wrapped into a
NativeJavaObject, which from JS perspective is an object, and Rhino
will (correctly) follow the JS equality semantics for objects, which
considers only reference-identical objects to be equal. This ain't
really Java specific, consider how even native object wrappers for JS
primitives will have reference identity equality semantics:
$ java -jar js.jar
Rhino 1.7 release 3 PRERELEASE 2009 07 06
js> new String("a") == new String("a")
false
js> new Number(2) == new Number(2)
false
However consider:
js> 2 == new Number(2)
true
js> new Number(2) == 2
true
js> "a" == new String("a")
true
js> new String("a") == "a"
true
Which is due to the fact that if any of the operands is a JS primitive
type (i.e. string, number) then the other will be coerced into a
primitive value and then the equality among primitive values will be
used instead.
Yeah, it's bloody un-intuitive, but that's the way JS works. Nothing
you can do about it.
Attila.
On 2009.07.07., at 21:46, Greg Brown wrote:
Hi all,
I have been working with Rhino a bit lately, and I have a couple of
questions:
1) When a Java object is used in an equality expression, I expected
the JavaScript == operator to invoke the object's equals() method,
and === to use Java's reference equality operator (==). However, it
appears that both == and === translate to reference equality;
equals() is only called if I invoke it explicitly. Is this the
expected behavior, or am I missing something?
2) If == does not currently delegate to equals(), should it? Taking
this one step further, would it be possible to support additional
operator overloads as well, a la Groovy?
http://groovy.codehaus.org/Operator+Overloading
For example, "a + b" translates to "a.plus(b)", "a - b" translates
to "a.minus(b)", etc.
Operator overloading is a feature that I have missed in Java (coming
from C++, way back) and many of the newer JVM scripting languages
support it (Groovy, Scala, JRuby (I think), and possibly others). It
would be really cool if Rhino supported it as well.
Greg
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