I have a concrete class which extends an abstract class, which in turn extends an abstract class. This top class implements an interface. Can I implement the interface method in the top abstract class, so that the concrete sub-class does not have to?
Also, if the interface method takes an Object type as it's parameter, can I have the implementation in the top abstract class take another type (which seems right to me), or would I have to use exactly the same method signature?
Can I implement the interface method in the top abstract class, so that the concrete sub-class does not have to?
Yes
Also, if the interface method takes an Object type as it's parameter, can I have the implementation in the top abstract class take another type (which seems right to me), or would I have to use exactly the same method signature?
It has to be the same signature. However, you can trick with generics, if you want to and if you explain your plan in more detail.
for your fist quetion
Can I implement the interface method in the top abstract class, so that the concrete sub-class does not have to?
you can and you should if its a common feature for all the subclasses.
below is the example for the same
interface X{
void show();
}
abstract class A implements X{
public void show(){
System.out.println("show");
}
}
abstract class B extends A{
}
class C extends B{
}
for your second question
No , signature must be same always.
so below program illustares it
interface X{
void print(Object obj);
}
abstract class A implements X{
@Override
public void print(Object obj) {
System.out.println("print");
}
}
below program wont compile if you change type in subclass
interface X{
void print(Object obj);
}
abstract class A implements X{
@Override
public void print(A obj) {
System.out.println("print");
}
}
