Is it possible to create an instance of a generic type in Java? I\'m thinking based on what I\'ve seen that the answer is no
(due to type erasure), but
You are correct. You can't do new E()
. But you can change it to
private static class SomeContainer<E> {
E createContents(Class<E> clazz) {
return clazz.newInstance();
}
}
It's a pain. But it works. Wrapping it in the factory pattern makes it a little more tolerable.
You can do this now and it doesn't require a bunch of reflection code.
import com.google.common.reflect.TypeToken;
public class Q26289147
{
public static void main(final String[] args) throws IllegalAccessException, InstantiationException
{
final StrawManParameterizedClass<String> smpc = new StrawManParameterizedClass<String>() {};
final String string = (String) smpc.type.getRawType().newInstance();
System.out.format("string = \"%s\"",string);
}
static abstract class StrawManParameterizedClass<T>
{
final TypeToken<T> type = new TypeToken<T>(getClass()) {};
}
}
Of course if you need to call the constructor that will require some reflection, but that is very well documented, this trick isn't!
Here is the JavaDoc for TypeToken.
package org.foo.com;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
/**
* Basically the same answer as noah's.
*/
public class Home<E>
{
@SuppressWarnings ("unchecked")
public Class<E> getTypeParameterClass()
{
Type type = getClass().getGenericSuperclass();
ParameterizedType paramType = (ParameterizedType) type;
return (Class<E>) paramType.getActualTypeArguments()[0];
}
private static class StringHome extends Home<String>
{
}
private static class StringBuilderHome extends Home<StringBuilder>
{
}
private static class StringBufferHome extends Home<StringBuffer>
{
}
/**
* This prints "String", "StringBuilder" and "StringBuffer"
*/
public static void main(String[] args) throws InstantiationException, IllegalAccessException
{
Object object0 = new StringHome().getTypeParameterClass().newInstance();
Object object1 = new StringBuilderHome().getTypeParameterClass().newInstance();
Object object2 = new StringBufferHome().getTypeParameterClass().newInstance();
System.out.println(object0.getClass().getSimpleName());
System.out.println(object1.getClass().getSimpleName());
System.out.println(object2.getClass().getSimpleName());
}
}