元空间和运行时常量池

It stores per-class structures such as the run-time
constant pool, field and method data, and the code for methods and constructors,
including the special methods used in class and interface initialization and in
instance initialization 

A run-time constant pool is a per-class or per-interface run-time representation
of the constant_pool table in a class file (§4.4). It contains several kinds of
constants, ranging from numeric literals known at compile-time to method and field
references that must be resolved at run-time. The run-time constant pool serves a
function similar to that of a symbol table for a conventional programming language,
although it contains a wider range of data than a typical symbol table.
Each run-time constant pool is allocated from the Java Virtual Machine‘s method
area (§2.5.4). The run-time constant pool for a class or interface is constructed
when the class or interface is created (§5.3) by the Java Virtual Machine.
The following exceptional condition is associated with the construction of the runtime constant pool for a class or interface:
? When creating a class or interface, if the construction of the run-time constant
pool requires more memory than can be made available in the method area of the
Java Virtual Machine, the Java Virtual Machine throws an OutOfMemoryError.
See §5 (Loading, Linking, and Initializing) for information about the construction of the
run-time constant pool.