Here are a few general guidelines for using object memory efficiently:
- Avoid creating objects in frequently used routines. Because these routines are called frequently, you will likely be creating objects frequently, and consequently adding heavily to the overall burden of object cycling. By rewriting such routines to avoid creating objects, possibly by passing in reusable objects as parameters, you can decrease object cycling.
- Try to presize any collection object to be as big as it will need to be. It is better for the object to be slightly bigger than necessary than to be smaller than it needs to be. This recommendation really applies to collections that implement size increases in such a way that objects are discarded. For example,
Vectorgrows by creating a new larger internal array object, copying all the elements from and discarding the old array. Most collection implementations have similar implementations for growing the collection beyond its current capacity, so presizing a collection to its largest potential size reduces the number of objects discarded. - When multiple instances of a class need access to a particular object in a variable local to those instances, it is better to make that variable a static variable rather than have each instance hold a separate reference. This reduces the space taken by each object (one less instance variable) and can also reduce the number of objects created if each instance creates a separate object to populate that instance variable.
- Reuse exception instances when you do not specifically require a stack trace (see ).
