Java Reflection calling constructor with primitive types

Question

I have a method in my test framework that creates an instance of a class, depending on the parameters passed in:

public void test(Object... constructorArgs) throws Exception {
    Constructor<T> con;
    if (constructorArgs.length > 0) {
        Class<?>[] parameterTypes = new Class<?>[constructorArgs.length];
        for (int i = 0; i < constructorArgs.length; i++) {
            parameterTypes[i] = constructorArgs[i].getClass();  
        }
        con = clazz.getConstructor(parameterTypes);
    } else {
        con = clazz.getConstructor();
    }
}

The problem is, this doesn't work if the constructor has primitive types, as follows:

public Range(String name, int lowerBound, int upperBound) { ... }

.test("a", 1, 3);

Results in:

java.lang.NoSuchMethodException: Range.<init>(java.lang.String, java.lang.Integer, java.lang.Integer)

The primitive ints are auto-boxed in to object versions, but how do I get them back for calling the constructor?

Answer 1

Use Integer.TYPE instead of Integer.class.

As per the Javadocs, this is "The Class instance representing the primitive type int."

Answer 2

To reference primitive types use, for example:

Integer.TYPE;

You will need to know which arguments passed into your method are primitive values. You can do this with:

object.getClass().isPrimitive()

Answer 3

If primitive int value is autoboxed into Integer object, it's not primitive anymore. You can't tell from Integer instance whether it was int at some point.

I would suggest passing two arrays into test method: one with types and another with values. It'll also remove ambiguity if you have a constructor MyClass(Object) and pass string value (getConstructor would be looking for String constructor).
Also, you can't tell expected parameter type if parameter value is null.