Create new instance of object's class

Question

Let's say I have an object called myCar that is an instance of Car.

myCar = new Car();

How would I do to create a new instance of that class based on the object? Let's say that I don't know which class myCar was created from.

otherObject = new myCar.getClass()(); // Just do demonstrate what I mean (I know this doesn't work)

UPDATE

public class MyClass {
    public MyClass(int x, int y, Team team) { }
    public MyClass() { }
}

Object arg = new Object[] {2, 2, Game.team[0]};

try {
    Constructor ctor = assignedObject.getClass().getDeclaredConstructor(int.class, int.class, Team.class);
    ctor.setAccessible(true);
    GameObject obj = (GameObject) ctor.newInstance(arg);

} catch (InstantiationException x) {
    x.printStackTrace();
} catch (IllegalAccessException x) {
    x.printStackTrace();
} catch (InvocationTargetException x) {
    x.printStackTrace();
} catch (NoSuchMethodException x) {
    x.printStackTrace();
}

I get the following error:

java.lang.IllegalArgumentException: wrong number of arguments

getDeclaredConstructor() works and finds my constructor with three args, but newInstance(arg) won't work for some reason, it says "wrong number of arguments". Any idea why?

Answer 1

With reflection

otherObject = myCar.getClass().newInstance();

Assuming your class has a default constructor. You can do more advanced operations with non default (empty) constructors

Constructor[] constructors = myCar.getClass().getConstructors();

And choose the one you want.

Read through this for more details about Java's Reflection capabilities.

Answer 2

You just call newInstance( on the class object:

Car newCar=myCar.getClass().newInstance();

You need a default constructor and you must also remember that any exceptions get wrapped in an InvocationTargetException .

If the class does not have a default constructor, this is not possible without a non-reflective factory or constructor.

InstantiationException - if this Class represents an abstract class, an interface, an array class, a primitive type, or void; or if the class has no nullary constructor

Answer 3

Through reflection. Use this:

myCar.getClass().newInstance();

Answer 4

Regarding your UPDATE/error - look here:

public class DupaReflect {

    private String name;
    private int id;

    private DupaReflect(String name, int id) {
        super();
        this.name = name;
        this.id = id;
    }

    @Override
    public String toString() {
        return "DupaReflect [name=" + name + ", id=" + id + "]";
    }

    public static void main(String[] args) throws Exception {
        Object[] objects = new Object[] { "asd", 1 };
        DupaReflect dupa = DupaReflect.class.getDeclaredConstructor(String.class, int.class).newInstance(objects);
        System.out.println(dupa);
    }

}

This works and produces desired output. DupaReflect [name=asd, id=1]

Object[] objects = new Object[]{"asd", 1}; - that's the reason why my code works and yours does not.

In your code you have:

Object arg = new Object[] {2, 2, Game.team[0]};

Object[] is indeed type of Object in java, but this changes 3-element array of some objects into single object being that array. So you try to create a new object not with 3 arguments, but with 1, thus the exception is thrown

SOLUTION: Declare your Object arg as Object[] args and all should work.