"Source code clarity improves with class nesting because you declare a class closer to those objects it must manipulate and allow that class's methods to directly access object fields and call object methods -- even private fields and methods -- of enclosing classes. To understand that benefit, consider a scenario in which a program must iterate over an array of Job objects that exist within an Employee object:"
"Because of this, inner class objects require an object of the enclosing class, while nested class objects do not. Nested classes, therefore, behave just like top-level classes, using the enclosing class to provide a package-like organization. In addition, nested classes have access to all members of the enclosing class."
"Editor's note: Robert Simmons continues his efforts to clarify confusion over the use of nested classes in Java in this week's installment, excerpted from Chapter 6 ("Nested Classes") of Hardcore Java. Robert discusses the somewhat troublesome limited-scope inner classes; one specific type within this category, known as anonymous classes; and the various problems programmers can encounter with limited-scope classes."
"Author's note: The use of nested classes in Java is a constant source of confusion for many programmers. Yet understanding nested classes is critical to such things as the proper implementation of UML composition relationships in Java. In addition, such understanding will help the professional developer unravel spaghetti code put out by other developers."
"This code declares a public static nested class. This nested class can access the various static members of the enclosing class. However, unlike inner classes, it cannot access any instance variables in the enclosing class. This is an important difference between static nested classes and inner classes. Formally, it can be said that an inner class is instance-scoped and a static nested class is class-scoped. The class scope of a static nested class makes it easier to use:"
"Inner classes are essentially classes defined inside other classes and act like members of the enclosing class. There are two varieties of inner classes, static inner classes and non-static ones. The difference is suggested in the name itself, the static inner classes are associated with the enclosing class (as any other static member) while inner classes are associated with the "object" of the enclosing class. We shall explore the difference further later. Inner classes are a phenomenon of the compiler. It converts the inner classes as plain classfiles with some strange class names, the virtual machine does not distinguish between regular class's and inner class's class files."
"One of the Sun Certified Java Programmer (SJCP) Exam's objectives is to declare and construct any kind of class, including top-level, nested top-level, and inner classes. You are obviously going to be asked questions about this in the exam. I will elaborate on this exam objective in detail, with the support of examples and code snippets. You will then have a correct understanding of top-level, nested top-level, and inner class concepts and will be able to solve every question that is related to this exam objective."
"In the first half of this article, we began examining the benefits of inner classes, such as adding a "facet" to the behavior of an enclosing class to enrich its interactions. Then we touched upon their ability to act as access control points, where the inner class can be used to provide controlled access to some resource or to define isolated callbacks. Here, we'll follow up on this point and move on to discuss callbacks "on the fly" and static inner classes."
