Verification link in the process of Java class loading

After the class is loaded into the system, the first task is linking operation, and verification is the key first step to ensure that the loaded bytecode is legal, reasonable and in line with the specifications. In the verification process of Java virtual machine, it is necessary to complete a number of complex checks to ensure that the format, semantics, bytecode and symbol reference of class data information are accurate.

Format verification

Format validation ensures that the class file starts with the correct magic number, the major version and minor version are compatible, and the length of each item of data is correct.

Semantic check

Semantic checking goes deep into bytecode, eliminating non-conforming codes and ensuring semantic correctness.

Byte code verification

Byte code verification is the most complicated part of the verification process. By analyzing the byte stream, we can judge its enforceability. Although the security of 100% cannot be guaranteed, obvious problems will be found as far as possible.

Symbol reference verification

Symbolic reference validation ensures that the referenced classes and methods do exist and that the current class has access rights. If the required class or method cannot be found, an error will be raised.

Importance of verification link

After these four verification links, the integrity and correctness of the class are guaranteed, which lays a solid foundation for the stable operation of the system.