GenericsReflectionTest.java

package cyrille.reflect;

import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.ArrayList;
import java.util.List;

import junit.framework.TestCase;

public class GenericsReflectionTest extends TestCase {

    public void testCollection() throws Exception {

        List<String> myParamterizedList = new ArrayList<String>();

        Class clazz = myParamterizedList.getClass();

        System.out.println(clazz);

        System.out.println("generic superclass");
        Type genericSuperclass = clazz.getGenericSuperclass();
        print(genericSuperclass);

        System.out.println("generic interfaces");
        Type[] types = clazz.getGenericInterfaces();
        for (Type type : types) {
            print(type);
        }

    }

    // Prints information about a type variable

    private static void print(TypeVariable v) {
        System.out.println("Type variable");
        System.out.println("Name: " + v.getName());
        System.out.println("Declaration: " + v.getGenericDeclaration());
        System.out.println("Bounds:");
        for (Type t : v.getBounds()) {
            print(t);
        }
    }

    // Prints information about a wildcard type
    private static void print(WildcardType wt) {
        System.out.println("Wildcard type");
        System.out.println("Lower bounds:");
        for (Type b : wt.getLowerBounds()) {
            print(b);
        }

        System.out.println("Upper bounds:");
        for (Type b : wt.getUpperBounds()) {
            print(b);
        }
    }

    // Prints information about a parameterized type
    private static void print(ParameterizedType pt) {
        System.out.println("Parameterized type");
        System.out.println("Owner: " + pt.getOwnerType());
        System.out.println("Raw type: " + pt.getRawType());

        for (Type actualType : pt.getActualTypeArguments()) {
            print(actualType);
        }
    }

    // Prints information about a generic array type
    private static void print(GenericArrayType gat) {
        System.out.println("Generic array type");
        System.out.println("Type of array: ");
        print(gat.getGenericComponentType());
    }

    /**
     * Prints information about a type. The nested if/else-if chain calls the appropriate overloaded
     * print method for the type. If t is just a Class, we print it directly.
     */
    private static void print(Type t) {
        if (t instanceof TypeVariable) {
            print((TypeVariable) t);
        } else if (t instanceof WildcardType) {
            print((WildcardType) t);
        } else if (t instanceof ParameterizedType) {
            print((ParameterizedType) t);
        } else if (t instanceof GenericArrayType) {
            print((GenericArrayType) t);
        } else {
            System.out.println(t);
        }
    }
}