JVM method return address

One 、 It stores the caller's pc Register value ：

Two 、 The end of a method , There are two ways ：

      1. Normal execution complete .

      2 An unhandled exception occurred , Abnormal exit .

3、 ... and 、 Either way, exit , After the method exits, it returns to the location where the method was called . When the method exits normally , Of the caller pc The value of the register is used as the return address , That is, the address of the next instruction that calls the method . And the abnormal exit , The return address is determined through the exception table , This part of information will not be saved in stack frame .

Four 、 Essentially , Fang The exit of the method is the process of the current stack frame out of the stack , In this case, we need to restore the local variable table of the upper method , The stack of operands , Push the return value into the operand stack of the caller's stack frame , Set up pc Register values, etc , Let the caller method continue to execute .

5、 ... and . The difference between a normal completion exit and an abnormal completion exit is that ： Exiting through an exception completion exit will not generate any return value for its upper level caller .

6、 ... and 、 Method exit instruction ：

  (1) The normal exit ：

a. The execution engine encountered a bytecode instruction returned by any method (return), There will be a return value passed to the upper level method caller , abbreviation Complete the exit normally .

b. type ： It depends on the actual data type of the return value of the method .

c.ireturn: The return value is boolean,byte,char,short,int

   lreturn: The return value is long.

   dreturn: The return value is double.

    freturn: The return value is flot

    areturn: The return value is Reference type

     return: The return value is void.

  (2) Abnormal exit :

a. Concept ： Exception encountered during method execution , And this exception is not handled in the method , That is, as long as no matching exception handler is found in the exception table of this method , Will cause the method to exit , abbreviation Abnormal completion exit .

b. Example ：

  In bytecode 4-8 Exception encountered in line , Use bytecode 11 Line exception handler .