RFR: 8280035: Use Class.isInstance instead of Class.isAssignableFrom where applicable

[ExE Boss]

On Mon, 21 Feb 2022 12:16:53 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

>> I've stared at the javadoc for Class.isAssignableFrom and Class.isInstance and if a non-null instance is used to get a non-null class they are PROBABLY the same but it is far from clear. The implementations of both are at least native and may be instrinsicified. The doc for Class.isAssignableFrom cites JLS 5.1.4 which in what I found is about primitives so I suspect it is woefully out of date 
>> https://docs.oracle.com/javase/specs/jls/se17/html/jls-5.html#jls-5.1.4
>> 
>> What client tests have you run that touch the code you are changing ?
>> 
>> In short I see insufficient value in the changes here and would prefer you drop the client part so I don't have to worry about it.
>
>>In short I see insufficient value in the changes here and would prefer you drop the client part so I don't have to worry about it.
> 
> I think, usage of `isInstance` is much clear for most java developers. Everyone knows about java _instanceof_ operator. And `isInstance` method javadoc is very straight forward: `This method is the dynamic equivalent of the Java language instanceof operator.`
> 
> Method `isAssignableFrom` is opposite: it brings unnecessary complexity in the code. And it's easy to confuse orders of parameters. Even JBS confirms that:
> 1. [Wrong isAssignableFrom test when adding Principal to Subject ](https://bugs.openjdk.java.net/browse/JDK-8034820)
> 2. [isAssignableFrom checks in KeyFactorySpi.engineGetKeySpec appear to be backwards](https://bugs.openjdk.java.net/browse/JDK-8254717)
> 3. [isAssignableFrom checks in AlgorithmParametersSpi.engineGetParameterSpec appear to be backwards](https://bugs.openjdk.java.net/browse/JDK-8279800)
> 
> So, it gives all 3 points to prefer isInstance method: it's shorter, it's clearer for most java developers, it's faster.

> @turbanoff
> > Method `isAssignableFrom` is opposite: it brings unnecessary complexity in the code. And it's easy to confuse orders of parameters. Even JBS confirms that:
> 
> Maybe we should add `Class::isSubclassOf(Class<?> that)` that performs `that.isAssignableFrom(this)`:

I have opened [JI‑9073064](https://bugs.openjdk.java.net/browse/JI-9073064 "[JI‑9073064] Add the method `Class::isSublassOf(Class<?>)` to `java.lang.Class` that does the inverse of `Class::isAssignableFrom`") for this.

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PR: https://git.openjdk.java.net/jdk/pull/7061