Is writing subclass inside the parent class same as writing subclass and referencing it to parent class using extends ?

Question

Is writing the subclass inside the parent class, the same as referencing the parent class using 'extends' while declaring the subclass ?
For example

class Animal{
boolean Is_Alive;
class dog{
private int legs = 4;
}
}

Is the above code same as writing

class Animal{
boolean Is_Alive;
}
class Dog extends Animal{
private int leg = 4
}

Thank you

Answer 1

If you define a subclass in a class this will be constructed with:

new Class.Subclass();

If you define a class which extends a class It isn't a member of that class. So you can construct that class only with the name:

new MyInheritedClass() ;

Answer 2

subclass always refers to the concept of inheritance, so you copy (and modify) the design of an existing class outside it, with the extends keyword.

When you create a class inside another class, it is called "nested class". The nested class can be static, or nonstatic "inner classes" (as one that can be instantiated). This is very different from a subclass.

Some design patterns, like the Singleton or Builder pattern, can be implemented with static inner classes.

More reading:
https://dzone.com/articles/what-are-nested-classes-and
https://docs.oracle.com/javase/tutorial/java/javaOO/whentouse.html
https://www.baeldung.com/creational-design-patterns