The document discusses minimizing accessibility of classes and members to increase encapsulation and modularity. It recommends making classes and members as inaccessible as possible based on their intended use and scope. Top-level classes can be public or package-private, while members should generally be private or package-private. Immutable classes are preferable to mutable ones. Composition should be favored over inheritance, and interfaces used only for defining types.

13. Sometimes we’ve to write classes that serve no purpose other than to group instance fields: class Point { public double x; public double y; }