Java/Encapsulation

Encapsulation: public/private.

Deciding what we expose to the outside world, versus what we keep protected, versus what we keep private:

Always make everything as private as possible.

If you find that it's difficult to thoroughly test a class, then the class may be doing too much. Splitting the class up using composition can make the individual units more testable.

A few heuristics:

• Decomposition
• Abstraction
• Subset identification
• Information hiding
• Virtual structuring
• Modularity
• Separating policy and mechanism
• Hierarchy

A few more heuristics:

• Visibility of system status - keep status of things visible to users.
• Match between system and world - keep verbiage and symbols system-oriented.
• User control - allow users ability to leave unwanted state.
• Consistency - maintain consistency across interfaces.
• Error prevention - try and anticipate and prevent errors.
• Recognition, not recall - make things visible, not things they have to retrieve
• Flexibility - things should be flexible across situations
• Accelerators - things unseen by novice users, allow speeding up interaction by expert users.
• Minimal - keep it simple.