scala - scala中空类的大小是多少？

Question

Scala 中空类的大小是多少？
我使用 SizeEstimator 来获取空类的大小。但是我得到的大小是 1368(字节)，看起来比我预期的要大得多。

Answer 1

你是指没有成员的类的 .class 文件的大小？

package mypackage

class EmptyClass {

}

对我来说，在使用 Java 1.8.0_121 的 Windows 上，使用 Scala 2.11，它是 527 字节(文件大小将根据包名称而变化，因为文件包含类和包名称)。

javap 工具显示文件中包含的数据:

$ javap -c -v -cp my-app/target/scala-2.11/classes mypackage.EmptyClass
Classfile /.../mypackage/EmptyClass.class
  Last modified 17-Jul-2017; size 527 bytes
  MD5 checksum d97a3d664755c085417b469bb84f982b
  Compiled from "EmptyClass.scala"
public class mypackage.EmptyClass
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Utf8               mypackage/EmptyClass
   #2 = Class              #1             // mypackage/EmptyClass
   #3 = Utf8               java/lang/Object
   #4 = Class              #3             // java/lang/Object
   #5 = Utf8               EmptyClass.scala
   #6 = Utf8               Lscala/reflect/ScalaSignature;
   #7 = Utf8               bytes
   #8 = Utf8               E1A!
                               \tQQ)9uscm]:
                                           \r\t\"\=qC\mZ3MA\t)i)1oY1mC&1:L(+4\t
                                                                               5\rqJg.?)yC\t
 = Utf8               <init>
  #10 = Utf8               ()V
  #11 = NameAndType        #9:#10         // "<init>":()V
  #12 = Methodref          #4.#11         // java/lang/Object."<init>":()V
  #13 = Utf8               this
  #14 = Utf8               Lmypackage/EmptyClass;
  #15 = Utf8               Code
  #16 = Utf8               LocalVariableTable
  #17 = Utf8               LineNumberTable
  #18 = Utf8               SourceFile
  #19 = Utf8               RuntimeVisibleAnnotations
  #20 = Utf8               ScalaInlineInfo
  #21 = Utf8               ScalaSig
{
  public mypackage.EmptyClass();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #12                 // Method java/lang/Object."<init>":()V
         4: return
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       5     0  this   Lmypackage/EmptyClass;
      LineNumberTable:
        line 5: 0
}
SourceFile: "EmptyClass.scala"
RuntimeVisibleAnnotations:
  0: #6(#7=s#8)
Error: unknown attribute
  ScalaInlineInfo: length = 0x9
   01 00 00 01 00 09 00 0A 00
Error: unknown attribute
  ScalaSig: length = 0x3
   05 00 00