Is it possible to create an instance of a derived class in abstract ancestor class using reflection Lets say:
abstract class Base {
public Base createInstance(){
//using reflection
Class<?> c = this.getClass();
Constructor<?> ctor = c.getConstructor();
return ((Base) ctor.newInstance());
}
}//end Base
class Derived extends Base {
main(){
new Derived().createInstance()
}
}
You can do this
public class Derived extends Base {
public static void main(String ... args) {
System.out.println(new Derived().createInstance());
}
}
abstract class Base {
public Base createInstance() {
//using reflection
try {
return getClass().asSubclass(Base.class).newInstance();
} catch (Exception e) {
throw new AssertionError(e);
}
}
}
prints
Derived@55fe910c
A more common pattern is to use Cloneable
public class Derived extends Base {
public static void main(String ... args) throws CloneNotSupportedException {
System.out.println(new Derived().clone());
}
}
abstract class Base implements Cloneable {
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
prints
Derived@8071a97
However, the need to use either should be avoided. Usually there is another way to do what you need so that base doesn't not implicitly depend on derived.
Proving it works is easy:
abstract class Base {
public Base createInstance() throws Exception {
return getClass().newInstance();
}
}
public class Derived extends Base {
public static void main(String[] args) throws Exception {
System.out.println(new Derived().createInstance().getClass());
}
}
prints
class test.Derived
You should ask yourself twice why you need it and whether it is really a good approach for your problem. If you need cloning, consider the clone mechanism, which does basically the same thing.
You can use Class.forName() and Class.newInstance() to create any class. But there's no way to easily identify subclasses of a class. See this JavaWorld tip for a technique to do this.
I think , however, the real issue is what is it you're ultimately trying to achieve, and can it be done more easily using conventional techniques.
public Base createInstance() { return (Base) getClass().newInstance(); }is all you need (module exceptions).