Reuse Objects

Reuse is the key to avoid creating unnecessary objects.

• Reuse immutable objects.
• Reuse mutable objects when you can.
  • If you know they are private and are not changed once created.
    • Make them private static final.
    • The impact on memory footprint and start-up time is most likely unobservable.
  • If it is not private but can be shared. (But be very careful!)
    • It is okay to share adapters that are backing the same object.
    • Say, keySet method of the Map interface.
• Watch autoboxing.
  • Prefer primitives to boxed primitives.
• Modern JVM is good at allocating lots POD-type of objects.
  • Maintaining your own object pool is generally a bad idea. Trust modern JVM’s highly optimized garbage collectors.
  • Unless it is a pool for extremely heavyweight objects, such as database connections.