java命令編譯java類、查看class文件內容

比如該java類：

public class SynchronizedDemo {
    public void method() {
        synchronized (this) {
            System.out.println("synchronized 代碼塊");
        }
    }
}

到java文件所在的目錄，執行javac命令：

javac SynchronizedDemo.java

會在在該目錄下會生成SynchronizedDemo.class文件

也可以通過-d參數指定生成class文件的目標目錄。

執行javap命令：

javap -c -s -v -l SynchronizedDemo.class

會顯示class的字節碼文件

Classfile /Users/wupengwei/IdeaProjects/webtest/src/main/java/com/wpw/web/base/SynchronizedDemo.class
  Last modified 2020-6-7; size 554 bytes
  MD5 checksum 42772ea478db21a81ac1e9853b3ca22b
  Compiled from "SynchronizedDemo.java"
public class com.wpw.web.base.SynchronizedDemo
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #6.#18         // java/lang/Object."<init>":()V
   #2 = Fieldref           #19.#20        // java/lang/System.out:Ljava/io/PrintStream;
   #3 = String             #21            // synchronized 代碼塊
   #4 = Methodref          #22.#23        // java/io/PrintStream.println:(Ljava/lang/String;)V
   #5 = Class              #24            // com/wpw/web/base/SynchronizedDemo
   #6 = Class              #25            // java/lang/Object
   #7 = Utf8               <init>
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               method
  #12 = Utf8               StackMapTable
  #13 = Class              #24            // com/wpw/web/base/SynchronizedDemo
  #14 = Class              #25            // java/lang/Object
  #15 = Class              #26            // java/lang/Throwable
  #16 = Utf8               SourceFile
  #17 = Utf8               SynchronizedDemo.java
  #18 = NameAndType        #7:#8          // "<init>":()V
  #19 = Class              #27            // java/lang/System
  #20 = NameAndType        #28:#29        // out:Ljava/io/PrintStream;
  #21 = Utf8               synchronized 代碼塊
  #22 = Class              #30            // java/io/PrintStream
  #23 = NameAndType        #31:#32        // println:(Ljava/lang/String;)V
  #24 = Utf8               com/wpw/web/base/SynchronizedDemo
  #25 = Utf8               java/lang/Object
  #26 = Utf8               java/lang/Throwable
  #27 = Utf8               java/lang/System
  #28 = Utf8               out
  #29 = Utf8               Ljava/io/PrintStream;
  #30 = Utf8               java/io/PrintStream
  #31 = Utf8               println
  #32 = Utf8               (Ljava/lang/String;)V
{
  public com.wpw.web.base.SynchronizedDemo();
    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 9: 0

  public void method();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=1
         0: aload_0
         1: dup
         2: astore_1
         3: monitorenter
         4: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
         7: ldc           #3                  // String synchronized 代碼塊
         9: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        12: aload_1
        13: monitorexit
        14: goto          22
        17: astore_2
        18: aload_1
        19: monitorexit
        20: aload_2
        21: athrow
        22: return
      Exception table:
         from    to  target type
             4    14    17   any
            17    20    17   any
      LineNumberTable:
        line 11: 0
        line 12: 4
        line 13: 12
        line 14: 22
      StackMapTable: number_of_entries = 2
        frame_type = 255 /* full_frame */
          offset_delta = 17
          locals = [ class com/wpw/web/base/SynchronizedDemo, class java/lang/Object ]
          stack = [ class java/lang/Throwable ]
        frame_type = 250 /* chop */
          offset_delta = 4
}
SourceFile: "SynchronizedDemo.java"

附：

javap命令參數：

-help  --help  -?        輸出此用法消息
  -version                 版本信息
  -v  -verbose             輸出附加信息
  -l                       輸出行號和本地變量表
  -public                  僅顯示公共類和成員
  -protected               顯示受保護的/公共類和成員
  -package                 顯示程序包/受保護的/公共類
                           和成員 (默認)
  -p  -private             顯示所有類和成員
  -c                       對代碼進行反彙編
  -s                       輸出內部類型簽名
  -sysinfo                 顯示正在處理的類的
                           系統信息 (路徑, 大小, 日期, MD5 散列)
  -constants               顯示靜態最終常量
  -classpath <path>        指定查找用戶類文件的位置
  -bootclasspath <path>    覆蓋引導類文件的位置