6.6 Performance Checklist

Most of these suggestions apply only after a bottleneck has been identified:

• Include all error-condition checking in blocks guarded by if statements.

• Avoid throwing exceptions in the normal code path of your application.

• Investigate whether a try-catch in the bottleneck imposes any extra cost.

• Use instanceof instead of making speculative class casts in a try-catch block.

• Consider throwing exceptions without generating a stack trace by reusing a previously created instance.

• Include any exceptions generated during the normal flow of the program when running performance tests.

• Assertions add overhead even when disabled, though an optimizing JIT compiler can eliminate the overhead (only HotSpot server mode succeeded in 1.4.0).

• Beware of adding assertions to quick, frequently called methods.

• Minimize casting.

• Avoid casts by creating and using type-specific collection classes.

• Use temporary variables of the cast type, instead of repeatedly casting.

• Type variables as precisely as possible.

• Use local variables rather than instance or static variables for faster manipulation.

• Use temporary variables to manipulate instance variables, static variables, and array elements.

• Use ints in preference to any other data type.

• Avoid long and double instance or static variables.

• Use primitive data types instead of objects for temporary variables.

• Consider accessing instance variables directly rather than through accessor methods. (But note that this breaks encapsulation.)

• Add extra method parameters when that would allow a method to avoid additional method calls.