How to get the class of type variable in Java Generics

Question

I\'ve seen similar questions but they didnt help very much.

For instance I\'ve got this Generic Class:

public class ContainerTest
{

    public          


        

Answer 1

There is a way to get the runtime type of the type parameter by using Guava's TypeToken to capture it. The solution's disadvantage is that you have to create an anonymous subclass each time you need an instance of Container.

class Container {

    TypeToken tokenOfContainedType = new TypeToken(getClass()) {};

    public Type getContainedType() {
        return tokenOfContainedType.getType();
    }
}

class TestCase {

    // note that containerTest is not a simple instance of Container,
    // an anonymous subclass is created
    private Container containerTest = new Container() {};

    @Test
    public void test() {
        Assert.assertEquals(String.class, containerTest.getContainedType());
    }
}

The key of this solution is described in tha JavaDoc of TypeToken's constructor used in the code above:

Clients create an empty anonymous subclass. Doing so embeds the type parameter in the anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.