How to create class instance by string name

Question

I want to create new class instance by a string variable, pass int[] as a parameter to this constructor, and save this instance in an array list.

What's more, that class derives from some other class, let's say Bar. And that array list is of type Bar. So:

    List<Bar> something = new ArrayList<Bar>();
    String name = "Foo";
    int[] arr = {1, 2, 3, 4, 5};
    try {
        Class myClass = Class.forName(name);
        Class[] types = {Integer.TYPE};
        Constructor constructor = myClass.getConstructor(types);
        Object[] parameters = {arr};
        Object instanceOfMyClass = constructor.newInstance(parameters);
        something.add(instanceOfMyClass);
    } catch(ClassNotFoundException e) {
        // handle it
    } catch(NoSuchMethodException e) {
        // handle it
    } catch(InstantiationException e) {
        // handle it
    } catch(IllegalAccessException e) {
        // handle it
    } catch(InvocationTargetException e) {
        // handle it
    }

This is what I've came up with, but unfortunately it doesn't work. How can I pass array of integers here (what would be the type)? How can I add this instance to the array list given here (it throws an error that I have to cast the instance of Foo class to Foo class)?

What line is throwing the error? What's the stack trace? (Or is this a compile-time error?) — Ted Hopp
– Ted Hopp, Commented Apr 20, 2014 at 17:49
Well, it doesn't actually matter, as only these two things were giving errors, and correcting it works, thanks! ;) — khernik
– khernik, Commented Apr 20, 2014 at 17:52

Jesper · Accepted Answer · 2014-04-20 17:47:13Z

4

Class[] types = {Integer.TYPE};
Constructor constructor = myClass.getConstructor(types);

This looks up a constructor that takes one int or Integer, not an array of ints.

If you want to lookup the constructor that takes an int[], then pass the correct arguments:

Class[] types = { int[].class };
Constructor constructor = myClass.getConstructor(types);

answered Apr 20, 2014 at 17:47

Jesper

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