AngelikaLanger.com - Memory Allocation and Garbage Collection in Java - Tutorial

ABSTRACT

In Java, allocation and deallocation of heap memory are handled by the virtual machine, i.e., by its memory manager and its garbage collector. This concept frees developers from the chores of explicit memory allocation and deallocation and eliminates the pitfalls that explicit memory management comes with, e.g. there are no memory leaks or dangling pointers in Java. Despite of this undeniable benefit, Java programs occasionally exhibit performance defects that are caused by excessive memory allocation or massive and time-consuming garbage collection. In order to eliminate these adverse effects on the program's overall performance, a Java developer needs an understanding of the memory allocation and garbage collection strategies of the JVM.

The tutorial gives an overview of various garbage collection algorithms employed by the Java virtual machine of Sun's JDK 6 including tips and tricks for tuning the garbage collector, use of memory profilers and garbage collection profilers. We will also briefly touch on escape analysis, which is an optimization technique used by the JVM to completely eliminate heap memory allocation and deallocation for certain objects.

Topics:

garbage collection principles and algorithms

mark-and-sweep, fragmentation and compaction
generational GC
parallel, concurrent and incremental GC

memory allocation an escape analysis

heap objects vs. stack objects

JVM profiling

profiling tools
profiling stragies
detection of unwanted references and loitering objects

GC profiling

GC profiling tools
GC tuning options