I need some eyes on this code.

[The Abrasive Sponge]

Shouldn't this work?


//Source Java 1.5/5.0
public class AssignableFromTest {

/** Creates a new instance of AssignableFromTest */
public AssignableFromTest() {
}

private static boolean isStandardProperty(Class<?> clazz) {
if (clazz.isPrimitive()) return true;
if (clazz.isAssignableFrom(Number.class)) return true;
if (clazz.isAssignableFrom(Character.class)) return true;
if (clazz.isAssignableFrom(String.class)) return true;
return false;
}

public static void main(String... args) {
Byte b = new Byte("0");
System.out.println(isStandardProperty(b.getClass())); //false?
Integer i = 4;
System.out.println(isStandardProperty(i.getClass())); //false?
}
}

 

[Ryan Stewart]

Shouldn't this work?

[...]
It works fine for me. What do you find to be wrong with it?

 

[The Abrasive Sponge]

Shouldn't this work?

[...]
It works fine for me. What do you find to be wrong with it?

Did you get 2 false or 2 true?

 

[Ryan Stewart]

Shouldn't this work?

[...]
It works fine for me. What do you find to be wrong with it?

Did you get 2 false or 2 true?

two false

 

[The Abrasive Sponge]

Shouldn't this work?

[...]
It works fine for me. What do you find to be wrong with it?

Did you get 2 false or 2 true?

two false

Hmm, I would of thought that it would be two true since Byte and Integer
are subclasses of Number.

 

[The Abrasive Sponge]

Ryan Stewart wrote:

message

Shouldn't this work?


[...]
It works fine for me. What do you find to be wrong with it?


Did you get 2 false or 2 true?

two false

Hmm, I would of thought that it would be two true since Byte and Integer
are subclasses of Number.

Nevermind I see why, just read the java doc.

 

[Ryan Stewart]

Hmm, I would of thought that it would be two true since Byte and Integer are
subclasses of Number.

But that's the reverse of what you're asking. Your code checks if "Byte is
assignable from Number" and if "Integer is assignable from Number". In code,
that would be:
Number n;
Byte b = n;
Integer i = n;

That won't work without explicit casting. Read the method contract in the
java.lang.Class docs.

 

[Ryan Stewart]

Nevermind I see why, just read the java doc.

Good

 

[Roland]

Ryan Stewart wrote:

message

Shouldn't this work?


[...]
It works fine for me. What do you find to be wrong with it?


Did you get 2 false or 2 true?

two false

Hmm, I would of thought that it would be two true since Byte and Integer
are subclasses of Number.

isAssignableFrom can be confusing. I always try to read it it the other
way round. So
if (clazz.isAssignableFrom(Number.class)) ...
would become
if [an instance of] Number.class can be assigned to [a variable of
type] clazz ... [then]

And this isn't what you expected it to do... ;-)
You probably want to test
if [an instance of] clazz can be assigned to [a variable of type]
Number ...

--
Regards,

Roland de Ruiter
___ ___
/__/ w_/ /__/
/ \ /_/ / \

 

[dar7yl]

Nevermind I see why, just read the java doc.

Darn, just when you had a theory all figured out, somebody has to go and
write the docs to bust it out of the water

regards,
Dar7yl