Reflection: invoke a method using Number as wrapper for premitives

Question

My task is to call the methods of java.lang.Math using a String with the necessary information. Since there are only methods using primitive number types I use Number as a wrapper, which then gets the value parsed from String.

Number value = null;
    switch (attributClass) {
        [...]//parse the attribute into "value"
    }
Method m = null;
try{
    m = Class.forName("java.lang.Math").getDeclaredMethod(mName, value.getClass());
...

now my problem is that I get the following exception:

java.lang.NoSuchMethodException: java.lang.Math.acos(java.lang.Double) at java.lang.Class.getDeclaredMethod(Unknown Source)

I suppose this happens because Double is not the primitive type double but is there any way to get the primitive from the Number?

Answer 1

There's no standard method for converting wrapper classes to primitive classes an vice versa to my knowledge.

A hacky way to get the primitive class of a wrapper class is wrapperClass.getDeclaredField("TYPE").get(null) (Because each wrapper defines such a field). If you don't want to do that you can create a Map<Class, Class> to map from wrappers to primitives and fill it with the 8 primitive types and their respective wrappers.

Answer 2

这似乎不那么明显，但是您可以使用primitive.class ，例如

m = Class.forName("java.lang.Math").getDeclaredMethod("min", int.class, int.class);