Almost Never Use Inner Class

Most likely, static member class or lambda expression is sufficient.

Java has four kinds of nested classes:

• Static member class.
• Non-static member class.
• Anonymous class.
• Local class.

The latter three together are called inner class. Inner class cannot exist without a reference to its enclosing object, which is an inconvenient limitation and sometime causes memory leak. I could only think of one legitimate use of inner class, which is returning a “view” of a collection, such as an iterator.