How can I get a Class object form primitive?

Question

Obviously this is possible (as Class has isPrimitive() method) but how I can do this directly? E.g. reflection api able to cast a primitive type to Class:

import java.lang.reflect.Method;


public class TestClass {
       
        public static void m(){}
        public static void m(Object o){}
        public static void m(int i){}
        public static void m(Integer i){}
       
        public static void main(String[] args){
               
                TestClass tc=new TestClass();
                Method[] mtds=tc.getClass().getDeclaredMethods();
               
                for (int i = 0; i < mtds.length; i++) {
                        System.out.print(mtds[i].getName());
                        Class[] prms=mtds[i].getParameterTypes();
                        for (int j = 0; j < prms.length; j++) {
                                System.out.print("-"+prms[j].getCanonicalName());
                                       
                        }
                        System.out.println();
                }        
        }
}

output is:

m

m-java.lang.Object

m-int

m-java.lang.Integer

main-java.lang.String[]

Integer and int are different so it is not autoboxing. Anything (except creating an utility class with reflection and getParameterTypes() ) do not come at my mind (everything else I've tried failed).

I don't understand your question. There are class literals for primitives. But given a primitive value (or rather a variable of a primitive type), you already know its type. You wouldn't need to use something similar to `getClass`. — Sotirios Delimanolis, Nov 23 '15 at 19:29
What has this to do with autoboxing? Can you tell what is your expected output? Not really clear. — Rohit Jain, Nov 23 '15 at 19:31
@RohitJain - my first thought was that `int` is wrapped to `Integer` so it will be possible to get the Class object from int.But obviously I was wrong :-) — npocmaka, Nov 23 '15 at 21:56

M A · Accepted Answer · 2015-11-23T19:34:03.923

3

For int you normally do int.class or Integer.TYPE. Similarly for the other primitive types (e.g. double.class).

edited Nov 23 '15 at 19:34

answered Nov 23 '15 at 19:29

M A

65,721
13
123
159

aah.Great! Didn't know this.Will accept this after 10 minmutes. – npocmaka Nov 23 '15 at 19:30
2

Even `void` has `void.class` and `Void.TYPE` – Peter Lawrey Nov 23 '15 at 19:32
@PeterLawrey - this is pretty interesting.Is there are cases where this can be useful? – npocmaka Nov 23 '15 at 19:41
How does and when `int.class` or `Integer.TYPE` be useful ?? If you could throw some light. – hagrawal Nov 23 '15 at 19:45
@hagrawal - for me it was useful with reflection as in the example- when I'm searching for a method with exact types of parameters. Though it is interesting how `void` could be useful for something (anyway it is good to know it). – npocmaka Nov 23 '15 at 19:50
1

@npocmaka http://stackoverflow.com/questions/2352447/what-is-the-need-of-void-class-in-java – M A Nov 23 '15 at 19:56
1

You can need `Main.class.getMethod("main", String[].class).getReturnType() == void.class` and also `Callable` if you have a callable which doesn't actually return anything. (It might throw a checked exception however so you can't use `Runnable` either) – Peter Lawrey Nov 23 '15 at 20:09

How can I get a Class object form primitive?

1 Answers1