Java Performance Tuning

Object Reuse

As we saw in the last section, objects are expensive to create. Where it is reasonable to reuse the same object, you should do so. You need to be aware of when not to call new. One fairly obvious situation is when you have already used an object and can discard it before you are about to create another object of the same class. You should look at the object and consider whether it is possible to reset the fields and then reuse the object, rather than throw it away and create another. This can be particularly important for objects that are constantly used and discarded: for example, in graphics processing, objects such as Rectangle s, Points, Colors, and Fonts are used and discarded all the time. Recycling these types of objects can certainly improve performance.

Recycling can also apply to the internal elements of structures. For example, a linked list has nodes added to it as it grows, and as it shrinks, the nodes are discarded. Holding on to the discarded nodes is an obvious way to recycle these objects and reduce the cost of object creation.

Pool Management

Most container objects (e.g., Vectors, Hashtables) can be reused rather than created and thrown away. Of course, while you are not using the retained objects, you are holding on to more memory than if you simply discarded those objects, and this reduces the memory available to create other objects. You need to balance the need to have some free memory available against the need to improve performance by ...