unable to understand new keyword in java

Question

Probably a very noob question

I am new to java and am reading a third party api written in java...

I came across this declaration

Foo foo = new FooBar().new Foo();

I am unable to understand

 FooBar().new

Why is this declaration like this?

What advantages does one get in declaring something like above and what are the alternatives to such declaration.

Any advice/references would be greatly appreciated.

THanks

Answer 1

FooBar contains an inner class like this

class FooBar {

    class Foo {
      ...
    }
}

A new instance of the outer class is required to instantiate the inner class. Some classes don't make sense on their own so are implemented as nested classes. Here Foo has a relationship with FooBar and also has the benefit of having access to all of the latter's member variables.