How to create an ArrayList of Classes?

Question

I have some classes (Car, Motorcycle, Train ... etc) that extends from class Vehicle. From another Class I need to create an ArrayList of Classes for access only to those that inlude the ArrayList.

The concept is similar to this, but obviously it doesn't work;

ArrayList<Class> vehicleType=new ArrayList<Class>();
vehicleType.add(Class.forName("train"));

How can I solve it ? Thanks

There's no reason why this shouldn't work. What error messages, if any, are you getting? — millimoose
– millimoose, Commented Oct 25, 2011 at 18:19
I'm not familiar with java, but does ArrayList<Vehicle> do what you want? — Mooing Duck
– Mooing Duck, Commented Oct 25, 2011 at 18:20
Maybe the class name is Train and your forName() call specified train, which doesn't match in the first letter? — Jim Garrison
– Jim Garrison, Commented Oct 25, 2011 at 18:21
A warning is not a problem. To get it to actually work, follow Dave's answer. I guess the warning you get is about the unparameterized Class reference. Use this: ArrayList<Class<? extends Vehicle>>. — G_H
– G_H, Commented Oct 25, 2011 at 18:30

Noel M · Accepted Answer · 2011-10-25 18:36:24Z

11

Most answers follow your suggestion of using Class.forName(), though that's not necessary. You can "call" .class on the type name.

Take a look at this JUnit test:

@Test
public void testListOfClasses() {

    List<Class<?>> classList = new ArrayList<Class<?>>();

    classList.add(Integer.class);
    classList.add(String.class);
    classList.add(Double.class);

    assertTrue("List contains Integer class", classList.contains(Integer.class));
}

I would expect for your need the list would be of type Class<? extends Vehicle>

edited Oct 25, 2011 at 18:36

answered Oct 25, 2011 at 18:30

Noel M

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Comments

Dave · Accepted Answer · 2011-10-25 18:25:09Z

3

If you're going to use the class loader (Class.forName), you need to use the fully qualified class name, i.e. Class.forName("com.package.Train");, exactly as you would reference it from the command line.

answered Oct 25, 2011 at 18:25

Dave

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Comments

Piotr Praszmo · Accepted Answer · 2011-10-25 18:31:39Z

2

Try:

ArrayList<Class<? extends Vehicle>> vehicleType=new ArrayList<? extends Vehicle>();
vehicleType.add(Train.class);

It will make sure that all classes added to vehicleType extend Vehicle. And, that class Train actually exists.

It's rarely necessary to use classes that way. Try finding a simpler way of solving your problem.

answered Oct 25, 2011 at 18:31

Piotr Praszmo

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Salvatore Previti · Accepted Answer · 2011-10-25 18:21:14Z

1

Class.forName("Train") perhaps? Case sensitive?

answered Oct 25, 2011 at 18:21

Salvatore Previti

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PeterMmm · Accepted Answer · 2011-10-25 18:30:18Z

0

If "train" is the simple class name then this will do the job

vehicleType.add(Class.forName(train.class.getName()));

Anyway while you don't tell us what is the error (or exception) message we cannot help further.

answered Oct 25, 2011 at 18:30

PeterMmm

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