Java Object Header

#为了防止自己忘记, remember, I always thought that "deep understanding of Java Virtual Machine" was written wrong.

In a hotspot virtual machine, the layout of objects stored in memory can be divided into 3 areas: Object Header (header), instance data (Instance), and aligned padding (Padding).

Which means Java Object = Object Header + Instance data + object fill

The object header is made up of two parts, one for storing its own run-time data, which is called Mark Word, the other is a type pointer, and the object pointer to its class metadata.

Object Header = Mark Word + type pointer

(in case of pointer compression not turned on)

In a 32-bit system, Mark Word = 4 bytes = Three Bits, object header = 8 bytes = bits;

In a 64-bit system, Mark Word = 8 bytes = Bits, object header = bytes = 128bits;

Java Object Header