《深入Java虚拟机学习笔记》- 第18章 finally子句

Compiled from "TryFinallyTest.java"
public class TryFinallyTest extends java.lang.Object{
public TryFinallyTest();
  Code:
   0:aload_0
   1:invokespecial#1; //Method java/lang/Object."<init>":()V4:return
 
private static int normal();
  Code:
   0:bipush10 
   2:istore_1
   3:bipush20
   5:ireturn
   6:astore_2
   7:bipush20
   9:ireturn
  Exception table:
   from   to  target type
     036   any
     676   any
//0-2 对应try子句，“3-5”及"7-9"表示finally子例程，而6表示编译器生成的catch处理过程的开端（这可以通过加粗的异常表看到）。
//注意我们没有看到关于return 10的任何信息，该语句已经被忽略了。 
public static void main(java.lang.String[]);
  Code:
   0:getstatic#2; //Field java/lang/System.out:Ljava/io/PrintStream;3:invokestatic#3; //Method normal:()I6:invokevirtual#4; //Method java/io/PrintStream.println:(I)V9:return
 
}

Compiled from "Surprise.java"
class Surprise extends java.lang.Object{
Surprise();
  Code:
   0:   aload_0
   1:   invokespecial   #8; //Method java/lang/Object."<init>":()V4:   return

static boolean surpriseTheProgrammer(boolean);
  Code:
   0:   iload_0
   1:   ifeq    84:   goto    87:   pop
   8:   iconst_0
   9:   ireturn
  Exception table:
   from   to  target type
     477   any

}

                            private
                            static
                            int
                             normal() {
        
                            int
                             a;
        
                            try
                             {
            a = 1;
            System.out.println("in try:set a to " + a);
            return a;
        } finally {
            a = 2;
            System.out.println("in finally:set a to " + a);
        }
    }

in try:set a to 1
in finally:set a to 2
1

private static int normal();
  Code:
   0:iconst_1
   1:istore_0   
//对应a=1(现在栈中压入常量1，再弹出存储到局部变量_0即a中)2:getstatic#2; //Field java/lang/System.out:Ljava/io/PrintStream;5:new#3; //class java/lang/StringBuilder8:dup
   9:invokespecial#4; //Method java/lang/StringBuilder."<init>":()V12:ldc#5; //String in try:set a to 14:invokevirtual#6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;17:iload_0
   18:invokevirtual#7; //Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;21:invokevirtual#8; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;24:invokevirtual#9; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
//9-24对应try块中的打印语句27:iload_0
   28:istore_1
//令人困惑的原因在这里-----编译器在try块中把变量a的值存在了标号为1的局部变量中，再跳到语句56我们就明白了，try中返回的是标号1的局部变量的值，而不是修改过的值。29:iconst_2
   30:istore_0
   31:getstatic#2; //Field java/lang/System.out:Ljava/io/PrintStream;34:new#3; //class java/lang/StringBuilder37:dup
   38:invokespecial#4; //Method java/lang/StringBuilder."<init>":()V41:ldc#10; //String in finally:set a to 43:invokevirtual#6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;46:iload_0
   47:invokevirtual#7; //Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;50:invokevirtual#8; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;53:invokevirtual#9; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
//29-53对应finally块56:iload_1
   57:ireturn
//56-57对应try中的return a.58:astore_2
   59:iconst_2
   60:istore_0
//59-60对应finally中的a=2;61:getstatic#2; //Field java/lang/System.out:Ljava/io/PrintStream;64:new#3; //class java/lang/StringBuilder67:dup
   68:invokespecial#4; //Method java/lang/StringBuilder."<init>":()V71:ldc#10; //String in finally:set a to 73:invokevirtual#6; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;76:iload_0
   77:invokevirtual#7; //Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;80:invokevirtual#8; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;83:invokevirtual#9; //Method java/io/PrintStream.println:(Ljava/lang/String;)V86:aload_2
   87:athrow
  Exception table:
   from   to  target type
     02958   any
    585958   any