Java Performance Tuning

Initialization

All chained constructors are automatically called when creating an object with new. Chaining more constructors for a particular object causes extra overhead at object creation, as does initializing instance variables more than once . Be aware of the default values that Java initializes variables to:

• null for objects

• 0 for integer types of all lengths (byte, char, short, int, long)

• 0.0 for float types (float and double)

• false for booleans

There is no need to reinitialize these values in the constructor (although an optimizing compiler should be able to eliminate the extra redundant statement). Generalizing this point: if you can identify that the creation of a particular object is a bottleneck, either because it takes too long or because a great many of those objects are being created, you should check the constructor hierarchy to eliminate any multiple initializations to instance variables.

You can avoid constructors by unmarshalling objects from a serialized stream, because deserialization does not use constructors. However, serializing and deserializing objects is a CPU-intensive procedure and is unlikely to speed up your application. There is another way to avoid constructors when creating objects, namely by creating a clone( ) of an object. You can create new instances of classes that implement the Cloneable interface using the clone() method. These new instances do not call any class constructor, thus allowing you to avoid the constructor initializations. ...