JVM探秘6--图解虚拟机栈的局部变量表和操作数栈工作流程

案例代码如下：

 public class JVMTest {

     public static Integer num = 10;

     public int add(int i){

         int j = 5;

         int k = i+j;

         j++;

         k = num + j;

         return k;

     }

     public static void main(String[] args){

         System.out.println(new JVMTest().add(4));

     }

 }

编译之后主要指令集如下：

 {

   public static java.lang.Integer num;

     descriptor: Ljava/lang/Integer;

     flags: ACC_PUBLIC, ACC_STATIC

   public com.lucky.grpc.JVMTest();

     descriptor: ()V

     flags: ACC_PUBLIC

     Code:

       stack=1, locals=1, args_size=1

          0: aload_0

          1: invokespecial #1                  // Method java/lang/Object."<init>":()V

          4: return

       LineNumberTable:

         line 3: 0

   public int add(int);

     descriptor: (I)I

     flags: ACC_PUBLIC

     Code:

       stack=2, locals=4, args_size=2

          0: iconst_5

          1: istore_2

          2: iload_1

          3: iload_2

          4: iadd

          5: istore_3

          6: iinc          2, 1

          9: getstatic     #2                  // Field num:Ljava/lang/Integer;

         12: invokevirtual #3                  // Method java/lang/Integer.intValue:()I

         15: iload_2

         16: iadd

         17: istore_3

         18: iload_3

         19: ireturn

       LineNumberTable:

         line 7: 0

         line 8: 2

         line 9: 6

         line 10: 9

         line 11: 18

   public static void main(java.lang.String[]);

     descriptor: ([Ljava/lang/String;)V

     flags: ACC_PUBLIC, ACC_STATIC

     Code:

       stack=3, locals=1, args_size=1

          0: getstatic     #4                  // Field java/lang/System.out:Ljava/io/PrintStream;

          3: new           #5                  // class com/lucky/grpc/JVMTest

          6: dup

          7: invokespecial #6                  // Method "<init>":()V

         10: iconst_4

         11: invokevirtual #7                  // Method add:(I)I

         14: invokevirtual #8                  // Method java/io/PrintStream.println:(I)V

         17: return

       LineNumberTable:

         line 15: 0

         line 16: 17

   static {};

     descriptor: ()V

     flags: ACC_STATIC

     Code:

       stack=1, locals=0, args_size=0

          0: bipush        10

          2: invokestatic  #9                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;

          5: putstatic     #2                  // Field num:Ljava/lang/Integer;

          8: return

       LineNumberTable:

         line 4: 0

 }

其中第17行到第41行是add方法的指令，接下来就一行一行图解虚拟机栈是如何执行的！

第一步：iconst_5  ：将int类型的常量5压入操作数栈

第二步：istore_2 ：将操作数栈顶中int类型数据放入局部常量表下标为2的位置，从0开始数也就是第三个位置

第三步：iload_1 ：

是

JVM探秘6--图解虚拟机栈的局部变量表和操作数栈工作流程的相关教程结束。