1、创建MyTest3类
public class MyTest3 {
public void test(){
try {
InputStream is = new FileInputStream("test.txt");
ServerSocket serverSocket = new ServerSocket(9999);
serverSocket.accept();
}catch (FileNotFoundException ex){
}catch (IOException ex){
} catch (Exception ex){
}finally {
System.out.println("finally");
}
}
}
然后生成字节码
D:workspacestudy jvm_demouildclassesjavamaincomexamplejvmytecode>javap -verbose MyTest3.class
Classfile /D:/workspace/study/ jvm_demo/build/classes/java/main/com/example/jvm/bytecode/MyTest3.class
Last modified 2019-6-29; size 1068 bytes
MD5 checksum a51a76cf80a500bc95a8d3d20f7d2a0e
Compiled from "MyTest3.java"
public class com.example.jvm.bytecode.MyTest3
SourceFile: "MyTest3.java"
minor version: 0
major version: 51
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #15.#35 // java/lang/Object."<init>":()V
#2 = Class #36 // java/io/FileInputStream
#3 = String #37 // test.txt
#4 = Methodref #2.#38 // java/io/FileInputStream."<init>":(Ljava/lang/String;)V
#5 = Class #39 // java/net/ServerSocket
#6 = Methodref #5.#40 // java/net/ServerSocket."<init>":(I)V
#7 = Methodref #5.#41 // java/net/ServerSocket.accept:()Ljava/net/Socket;
#8 = Fieldref #42.#43 // java/lang/System.out:Ljava/io/PrintStream;
#9 = String #44 // finally
#10 = Methodref #45.#46 // java/io/PrintStream.println:(Ljava/lang/String;)V
#11 = Class #47 // java/io/FileNotFoundException
#12 = Class #48 // java/io/IOException
#13 = Class #49 // java/lang/Exception
#14 = Class #50 // com/example/jvm/bytecode/MyTest3
#15 = Class #51 // java/lang/Object
#16 = Utf8 <init>
#17 = Utf8 ()V
#18 = Utf8 Code
#19 = Utf8 LineNumberTable
#20 = Utf8 LocalVariableTable
#21 = Utf8 this
#22 = Utf8 Lcom/example/jvm/bytecode/MyTest3;
#23 = Utf8 test
#24 = Utf8 is
#25 = Utf8 Ljava/io/InputStream;
#26 = Utf8 serverSocket
#27 = Utf8 Ljava/net/ServerSocket;
#28 = Utf8 StackMapTable
#29 = Class #47 // java/io/FileNotFoundException
#30 = Class #48 // java/io/IOException
#31 = Class #49 // java/lang/Exception
#32 = Class #52 // java/lang/Throwable
#33 = Utf8 SourceFile
#34 = Utf8 MyTest3.java
#35 = NameAndType #16:#17 // "<init>":()V
#36 = Utf8 java/io/FileInputStream
#37 = Utf8 test.txt
#38 = NameAndType #16:#53 // "<init>":(Ljava/lang/String;)V
#39 = Utf8 java/net/ServerSocket
#40 = NameAndType #16:#54 // "<init>":(I)V
#41 = NameAndType #55:#56 // accept:()Ljava/net/Socket;
#42 = Class #57 // java/lang/System
#43 = NameAndType #58:#59 // out:Ljava/io/PrintStream;
#44 = Utf8 finally
#45 = Class #60 // java/io/PrintStream
#46 = NameAndType #61:#53 // println:(Ljava/lang/String;)V
#47 = Utf8 java/io/FileNotFoundException
#48 = Utf8 java/io/IOException
#49 = Utf8 java/lang/Exception
#50 = Utf8 com/example/jvm/bytecode/MyTest3
#51 = Utf8 java/lang/Object
#52 = Utf8 java/lang/Throwable
#53 = Utf8 (Ljava/lang/String;)V
#54 = Utf8 (I)V
#55 = Utf8 accept
#56 = Utf8 ()Ljava/net/Socket;
#57 = Utf8 java/lang/System
#58 = Utf8 out
#59 = Utf8 Ljava/io/PrintStream;
#60 = Utf8 java/io/PrintStream
#61 = Utf8 println
{
public com.example.jvm.bytecode.MyTest3();
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 9: 0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lcom/example/jvm/bytecode/MyTest3;
public void test();
flags: ACC_PUBLIC
Code:
stack=3, locals=4, args_size=1
0: new #2 // class java/io/FileInputStream
3: dup
4: ldc #3 // String test.txt
6: invokespecial #4 // Method java/io/FileInputStream."<init>":(Ljava/lang/String;)V
9: astore_1
10: new #5 // class java/net/ServerSocket
13: dup
14: sipush 9999
17: invokespecial #6 // Method java/net/ServerSocket."<init>":(I)V
20: astore_2
21: aload_2
22: invokevirtual #7 // Method java/net/ServerSocket.accept:()Ljava/net/Socket;
25: pop
26: getstatic #8 // Field java/lang/System.out:Ljava/io/PrintStream;
29: ldc #9 // String finally
31: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
34: goto 84
37: astore_1
38: getstatic #8 // Field java/lang/System.out:Ljava/io/PrintStream;
41: ldc #9 // String finally
43: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
46: goto 84
49: astore_1
50: getstatic #8 // Field java/lang/System.out:Ljava/io/PrintStream;
53: ldc #9 // String finally
55: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
58: goto 84
61: astore_1
62: getstatic #8 // Field java/lang/System.out:Ljava/io/PrintStream;
65: ldc #9 // String finally
67: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
70: goto 84
73: astore_3
74: getstatic #8 // Field java/lang/System.out:Ljava/io/PrintStream;
77: ldc #9 // String finally
79: invokevirtual #10 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
82: aload_3
83: athrow
84: return
Exception table:
from to target type
0 26 37 Class java/io/FileNotFoundException
0 26 49 Class java/io/IOException
0 26 61 Class java/lang/Exception
0 26 73 any
LineNumberTable:
line 13: 0
line 15: 10
line 16: 21
line 24: 26
line 25: 34
line 17: 37
line 24: 38
line 25: 46
line 19: 49
line 24: 50
line 25: 58
line 21: 61
line 24: 62
line 25: 70
line 24: 73
line 26: 84
LocalVariableTable:
Start Length Slot Name Signature
10 16 1 is Ljava/io/InputStream;
21 5 2 serverSocket Ljava/net/ServerSocket;
0 85 0 this Lcom/example/jvm/bytecode/MyTest3;
StackMapTable: number_of_entries = 5
frame_type = 101 /* same_locals_1_stack_item */
stack = [ class java/io/FileNotFoundException ]
frame_type = 75 /* same_locals_1_stack_item */
stack = [ class java/io/IOException ]
frame_type = 75 /* same_locals_1_stack_item */
stack = [ class java/lang/Exception ]
frame_type = 75 /* same_locals_1_stack_item */
stack = [ class java/lang/Throwable ]
frame_type = 10 /* same */
}
查看test方法
stack=3：表示操作数栈的最大深度为3
locals=4： 声明的局部变量的数目为4
args_size=1: 方法本身接收到的参数的数量
思考1：test方法没有接收参数，但是args_size=1表示接收参数为1 ？
对于Java类中的每一实例方法（非static方法），其在编译后所生成的字节码当中，方法参数的数量总是会比源代码中方法参数的数量多一个(this),它位于方法的第一个参数位置处； 这样，我们就可以在Java的实例方法中使用this来去访问当前对象的属性以及其他方法。
这个操作是在编译期间完成的，即由javac编译期在编译的时候将对this的访问转化为对一个普通实例方法参数的访问，接下来在运行期间，由JVM在调用实例方法时，自动向实例方法传入this参数。所以，在实例方法的局部表里表中，至少会有一个指向当前对象的局部变量。
思考2： locals=4，声明的局部变量的数目为4，分别是哪4个？
this，is， serverSocket，ex
stack=3,操作数栈的最大深度
2、异常表
如下图的三个异常
Java字节码对于异常的处理方式：
1、统一采用异常表的方式来对异常进行处理
2、在jdk1.4.2之前的的版本中，并不是对异常表的方式来对异常进行处理的，而是采用特定的指令方式
3、当异常处理存在finally语句块时，现代化的JVM采取的处理方式是将finally语句块的字节码拼接到每一个catch块后面
换句话说，程序中存在多少个catch块，就会在每一个catch块后面重复多少个finally语句的字节码
然后在方法里抛出异常，
反编译后查看
