Question

I saw these codes.

I’ve never seen such constructor, but I guess that it creates a new A instance with the implementation of a abstract method.

what is it called?

new A() {
    @Override
    public void onEvent() {
        dosomething();
    }
};

Answer 1

are you referring to an anonymous class? Its when you provide an implementation but never define a named class. In other words, you are providing an object in-place; you cannot reuse that definition elsewhere because you never wrote class MyClass {}, which is why it’s “anonymous”.

See this.