Nested classes are classes that are declared as members of other classes or scopes. Nesting classes is one way to better organize your code. For example, say you have a non-nested class (also known as ...

How can we debug method calls that are not part of our own source code, say a call to JButton.setEnabled()? Java provides us with anonymous inner classes, which come in quite handy for this problem.

Thanks to Java's anonymous (inner) classes, first-class functions (including environment capture) are indeed syntactic sugar that provide no additional expressive power. That's one way to look at it.