getting a class if i know the class name

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Marc E - 26 Nov 2005 21:31 GMT

I have a String whose value is "float". I need to turn that into float.class
for passing into a method (I need to do this for a number of
primitives....int, boolean, float, double, etc). Is there a built in way to
do this? Nothing jumped out at me in the Class class

thanks.

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Chris - 26 Nov 2005 22:01 GMT

>I have a String whose value is "float". I need to turn that into
>float.class for passing into a method (I need to do this for a number of
>primitives....int, boolean, float, double, etc). Is there a built in way
>to do this? Nothing jumped out at me in the Class class

First, think hard about why you're doing this. Manipulation of Class objects
is usually a bad idea if there is some other way to handle the problem.

That having been said, this may do the trick:

Class floatClass = Class.forName("java.lang.Float");

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Marc E - 26 Nov 2005 22:12 GMT

I was doing this as a small experiment with reflection and calling
method.invoke. the arguments to the methods are primitive floats, ints, and
booleans, and so I had to pass float.class as the Class [] params to find
the method thorugh reflection. I tried forName("java.lang.float") but of
course got an error. I'll give yours a shot.

thanks.

>>I have a String whose value is "float". I need to turn that into
>>float.class for passing into a method (I need to do this for a number of
[quoted text clipped - 8 lines]
>
> Class floatClass = Class.forName("java.lang.Float");

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Chris Smith - 26 Nov 2005 22:32 GMT

> I was doing this as a small experiment with reflection and calling
> method.invoke. the arguments to the methods are primitive floats, ints, and
> booleans, and so I had to pass float.class as the Class [] params to find
> the method thorugh reflection. I tried forName("java.lang.float") but of
> course got an error. I'll give yours a shot.

There's a difference between the Class object for Float and the Class
object for the primitive float. The code that Chris posted won't do the
same thing as what you've written.

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Roedy Green - 26 Nov 2005 22:45 GMT

>Class floatClass = Class.forName("java.lang.Float");

that is the Float class. Float.class is not the same as float.class.
float.class represents the primitive in a kludgy sort of way.

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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NullBock - 26 Nov 2005 22:34 GMT

So am I understanding you correctly? You want to use reflection for
calling a method with a primitive argument? This isn't a problem. Use
the TYPE field in the wrapper class associated with the primitive:

System.out.println(Float.TYPE);

output: float

Thus, if you wanted to call the Date(long) ctor, you would do something
like this:

Constructor ctor = Date.class.getConstructor(new Class[] {
Long.TYPE
});
Object[] args = {
new Long(0)
};
Date d = (Date) ctor.newInstance(args);

Is this what you want?

Walter Gildersleeve
Freiburg, Germany

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Roedy Green - 26 Nov 2005 22:44 GMT

>I have a String whose value is "float". I need to turn that into float.class
>for passing into a method (I need to do this for a number of
>primitives....int, boolean, float, double, etc). Is there a built in way to
>do this? Nothing jumped out at me in the Class class

I think you need a little HashMap to convert String to class literal.

You could see what pops out with Class.forName.

See http://mindprod.com/jgloss/classforname.html

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Oliver Wong - 28 Nov 2005 20:31 GMT

Class.forName();

http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Class.html#forName(java.lang.String)

Not sure if it works for primitives, but you can probably get
Float.class instead of float.class.

- Oliver

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Thomas Hawtin - 28 Nov 2005 20:55 GMT

> Class.forName();
>
> http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Class.html#forName(java.lang.String)
>
> Not sure if it works for primitives, but you can probably get
> Float.class instead of float.class.

No it doesn't work. Class.forName("float") will attempt to find the
class float, strangely enough. Using a map is probably the best bet.

In any case, it is usually more appropriate to write something along the
lines of:

Class clazz = Class.forName(
className, true, Thread.currentThread().getContextClassLoader()
);

Tom Hawtin

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getting a class if i know the class name

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