有如下代码
public class Test { public void work() { try { InputStream is = new FileInputStream("test.txt"); ServerSocket serverSocket = new ServerSocket(9999); serverSocket.accept(); } catch (FileNotFoundException e) { } catch (IOException e) { } catch (Exception e) { } finally { System.out.println("finally block"); } } }
javap -verbose -p Test 结果如下
D:\workspace-learn\common-learn\learn-classloader\target\classes\com\learn\jvm>javap -verbose -p Test 警告: 二进制文件Test包含com.learn.jvm.Test Classfile /D:/workspace-learn/common-learn/learn-classloader/target/classes/com/learn/jvm/Test.class Last modified 2019-9-5; size 1075 bytes MD5 checksum 744e2b9632f4d7f2d38d6b77b4225cc2 Compiled from "Test.java" public class com.learn.jvm.Test SourceFile: "Test.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 block #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/learn/jvm/Test #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/learn/jvm/Test; #23 = Utf8 work #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 Test.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 block #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/learn/jvm/Test #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.learn.jvm.Test(); 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 14: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 this Lcom/learn/jvm/Test; public void work(); 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 block 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 block 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 block 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 block 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 block 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 37 38 73 any 49 50 73 any 61 62 73 any 73 74 73 any LineNumberTable: line 17: 0 line 18: 10 line 19: 21 line 27: 26 line 28: 34 line 20: 37 line 27: 38 line 28: 46 line 22: 49 line 27: 50 line 28: 58 line 24: 61 line 27: 62 line 28: 70 line 27: 73 line 29: 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/learn/jvm/Test; 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 */ }
在上图中看到work方法的 stack=3, locals=4, args_size=1，其中size = 1表示参数个数为一个，即this，locals=4表示有4个局部变量，分别为 this，is，serverSocket，和 e，虽然有三个catch块，但是程序运行时只可能进入其中某一个，所以只有一个e
来源：博客园
作者：LonelyAsh
链接：https://www.cnblogs.com/heben/p/11470675.html