find constructor which has a generic parameter

Question

how can I find the constructor of a class which get passed a generic parameter. For example such a class:

class myClass<T> {
    public myClass(T val1, Long val2 String val3){ 
        ...
    }
}

Using the usual reflection approach getConstructor() lacks the proper parameters:

Constructor<?> myConstructor = myClass.class.getConstructor( ??what here??, Long.class, String.class);

Any ideas??

score 6 · Answer 1 · edited May 23 '17 at 12:23

Object is the type: Object.class

Because of generic type erasure, there is no other more specific type available.

More good stuff here: get-type-of-a-generic-parameter-in-java-with-reflection

e.g., for

public class Bar<T> {
   private T t;

   public Bar(T t) {
      this.t = t;
   }

   @Override
   public String toString() {
      return t.toString();
   }
}

This will return "foo":

Class<?>[] paramArray = {Object.class};
Constructor<?> myConstructor = Bar.class.getConstructor(paramArray);
String foo = "foo";
Bar myBar = (Bar) myConstructor.newInstance(foo);
System.out.println(myBar);

score -1 · Answer 2 · answered Oct 23 '13 at 16:09

-1

It's fairly straight forward.

Constructor<T> myConstructor = myClass.class.getConstructor( T val, Long.class, String.class);

If you want a string, it looks like this:

Constructor<String> myConstructor = myClass.class.getConstructor( String val, Long.class, String.class);

If you want a int, it looks like this:

Constructor<int> myConstructor = myClass.class.getConstructor( int val, Long.class, String.class);

answered Oct 23 '13 at 16:09

Dom

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ints can't be used as a generic, you have to use Integer. That last example would be Constructor... – LadyCailin Oct 23 '13 at 16:41
Have you tested this code? Does this even compile: `myClass.class.getConstructor( String val, Long.class, String.class);`? – Hovercraft Full Of Eels Oct 23 '13 at 16:52

find constructor which has a generic parameter

2 Answers2