CompressedOops - HotSpot Internals for OpenJDK - Oracle Wiki
Comment: What's an oop? An "oop", or "ordinary object pointer" in HotSpot parlance is a managed pointer to an object. It is normally the same size as a native machine pointer. A managed pointer is carefully tracked by the Java application and GC subsystem, so that storage for unused objects can be reclaimed. This process can also involve relocating (copying) objects which are in use, so that storage can be compacted. The term "oop" is traditional to certain VMs that derive from Smalltalk and Self, including the following: Self (an prototype-based relative of Smalltalk) https://github.com/russellallen/self/blob/master/vm/src/any/objects/oop.hh Strongtalk (a Smalltalk implementation) http://code.google.com/p/strongtalk/wiki/VMTypesForSmalltalkObjects V8 http://code.google.com/p/v8/source/browse/trunk/src/objects.h (mentions "smi" but not "oop") (In some of these systems, the term "smi" refers to a special non-oop word, a pseudo-pointer, which encodes a small, 30-bit integer.Read full article from CompressedOops - HotSpot Internals for OpenJDK - Oracle Wiki
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