Java Performance Tuning

Chapter 4. Object Creation

The biggest difference between time and space is that you can’t reuse time.

—Merrick Furst

“I thought that I didn’t need to worry about memory allocation. Java is supposed to handle all that for me.” This is a common perception, which is both true and false. Java handles low-level memory allocation and deallocation and comes with a garbage collector. Further, it prevents access to these low-level memory-handling routines, making the memory safe. So memory access should not cause corruption of data in other objects or in the running application, which is potentially the most serious problem that can occur with memory access violations. In a C or C++ program, problems of illegal pointer manipulations can be a major headache (e.g., deleting memory more than once, runaway pointers, bad casts). They are very difficult to track down and are likely to occur when changes are made to existing code. Java deals with all these possible problems and, at worst, will throw an exception immediately if memory is incorrectly accessed.

However, Java does not prevent you from using excessive amounts of memory nor from cycling through too much memory (e.g., creating and dereferencing many objects). Contrary to popular opinion, you can get memory leaks by holding on to objects without releasing references. This stops the garbage collector from reclaiming those objects, resulting in increasing amounts of memory being used.^[27] In addition, Java does not provide for large numbers ...