Java. String contents to create an object's instance

Question

I know this is part of java.lang.reflect.* but I wasn't able to find any suggestions to point me how to tackle this.

I want to use the contents of a string to create and instance of an object that has the name of what the string stores.

Eg.
String[] carName = {"volvo","vw","bmw"};
car carName[0];
car carName[1];
car carName[2];

I've stumbled upon this snippet, which looks promising:
Car car = (Car) Class.forName("Volvo").newInstance();
It throws back: Unhandled exception type ClassNotFoundException

edit: Sorry for not being clear enough, I'm not in any way a professional. No, I don't have a class called Volvo. I'm actually trying to define one generic class (car) and then initialize instances of it via strings.

That's a compilation error. This is not a reflection question, this is a question about getting java to compile. — skaffman
– skaffman, Commented Jan 20, 2011 at 23:14
Is there a reason you're doing this using reflection like this? If it's an exercise fair enough. Otherwise though, I personally wouldn't use it. By using Class.forName() you're forcing your users to input the exact name of the class (case sensitive, no extra characters or anything else, and it can never contain spaces.) I'd at least have a map of string=>class name somewhere that you maintain, that way you can still instantiate objects reflectively but the name to get to that class becomes much more flexible. — Michael Berry
– Michael Berry, Commented Jan 21, 2011 at 0:25

Bozho · Accepted Answer · 2011-01-20 23:16:15Z

4

You need to either catch the ClassNotFoundException, or declare it to be thrown from your method
You need to specify the fully-qualified name of your class. If the class is in packaged as foo.cars.Volvo, then use that as its name.

answered Jan 20, 2011 at 23:16

Bozho

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bluish · Accepted Answer · 2012-10-12 09:14:09Z

3

It looks as if the class you reference isn't on the classpath. Make sure you reference the full package, e.g.

com.example.Volvo

when using Class.forName().

edited Oct 12, 2012 at 9:14

bluish

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answered Jan 20, 2011 at 23:15

Jonathan Holloway

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John Gardner · Accepted Answer · 2011-01-21 17:25:09Z

0

Do you have a class called Volvo which extends Car?

Class.forName requires a fullly qualified classname, so it might be org.example.Volvo or whatever you've named your class.

Or are you trying to create a new car object that has a value of carName?

Edit:

Then what you're looking for is probably more like (i didn't try to compile this, so...)

string[] names = { "Volvo", "BMW", "Volkswagen" };
List<Car> cars = new ArrayList<Car>();

for(string name : cars)
{
    // presuming you have a class Car with a constructor that takes a string
    cars.Add(new Car(name));
}

if you already know you have a class called car, you don't need to mess with any of the reflection stuff to create one.

edited Jan 21, 2011 at 17:25

answered Jan 20, 2011 at 23:16

John Gardner

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1 Comment

user583728 Over a year ago

No, I don't have a class called Volvo. I'm actually trying to define one generic class (car) and then initialize instances of it via strings.

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