Java Base b = new Derived（）; 继承问题

Question

What exactly happens when you create a new instance using :

Base b = new Derived();

I cannot really understand the mechanics behind this.

Answer 1

Basically, from that point the compiler sees a Base instance and in runtime the instance is of type Derived .

In a broader explanation the Base type might be a interface, so you know by the contract what method has and what it does Polymorphism . But you are abstracted from the implementation.

Answer 2

The reference to b is type Base . But the implementation is Derived . This means you can use it as a Base but it will behave as a Derived . Doing b instanceof Derived will be true because the implementation is of type Derived