java try finally 字节码解析 |

11月 24, 2021 | Nix.Huang

    public static void main(String[] args) {
        int i = 5;
        try{
            i = 7;
        } catch (Throwable e) {
        }finally {
            i = 8;
        }
    }

public static void main(String[] args) {

int i = 5;

try{

i = 7;

} catch (Throwable e) {

}finally {

i = 8;

}

javap -c -p TestDynamicInvoke.class 反编译结果

  public static void main(java.lang.String[]);
    Code:
       0: iconst_5
       1: istore_1
       2: bipush        7
       4: istore_1
       5: bipush        8
       7: istore_1
       8: goto          24
      11: astore_2
      12: bipush        8
      14: istore_1
      15: goto          24
      18: astore_3
      19: bipush        8
      21: istore_1
      22: aload_3
      23: athrow
      24: return
    Exception table:
       from    to  target type
           2     5    11   Class java/lang/Throwable
           2     5    18   any

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

Code:

0: iconst_5

1: istore_1

2: bipush 7

4: istore_1

5: bipush 8

7: istore_1

8: goto 24

11: astore_2

12: bipush 8

14: istore_1

15: goto 24

18: astore_3

19: bipush 8

21: istore_1

22: aload_3

23: athrow

24: return

Exception table:

from to target type

2 5 11 Class java/lang/Throwable

2 5 18 any

使用一种叫做冗余技术，如果没有发生异常，finally 块对应5,7行代码，如果2-5行之间发生被捕获异常那么从11行开始执行，如果是未被捕获的异常从18行开始执行，可以看到finally块的字节码被冗余了3次，也就是总共会有2(正常流程+自动生成的catch any)+n(catch异常的次数)

Posted in: java基础

知行合一，止于至善

java try finally 字节码解析

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