Question

It was difficult to search for information on this because I don’t know what it’s called, so that’s my first question I guess.

Does the use of this notation:

new Object() {//code here}

create a new object of type Object or create a new object that is a subclass of object? If it is a subclass, can you put everything you could use to declare a class (member variables, functions, inner classes), inside the braces? Could you even write a constructor for it?

Answer 1

This is called an anonymous class. Basically, you’re defining a subclass in-place.

This call:

Object a = new Object() {
   // stuff
};

.. defines a new subclass of Object with //stuff in it (just like declaring that in a normal A extends Object.

Wikipedia has a good article about them too.

They’re useful primarily for closures, which means that the functions defined in your anonymous class have access to final variables from the enclosing scope.

Example-ish:

interface Function {
    void run();
}

static void example(Function f) {
    f.run();
}

void runExample() {
    final int a = 10;
    example(new Function() {
        void run() {
            // Notice that "a" was defined in the outer scope
            System.out.println(a);
        }
    });
}