首页 \ 问答 \ 生成不同的字节码问题(Different byte code generated issue)

生成不同的字节码问题(Different byte code generated issue)

 我试图在布尔值上进行模式匹配。 我已经编写了相同的方法稍作修改，但它们的字节码生成有很大差异。 
 

 例如 
 

scala> def compare(flag: Boolean) = {
     | flag match{
     | case true => println("true..")
     | case false => println("false...")
     | }}
compare: (flag: Boolean)Unit

scala> :javap -c compare
Compiled from "<console>"
public class $line4.$read$$iw$$iw$ {
  public static $line4.$read$$iw$$iw$ MODULE$;

  public static {};
    Code:
       0: new           #2                  // class $line4/$read$$iw$$iw$
       3: invokespecial #17                 // Method "<init>":()V
       6: return

  public void compare(boolean);
    Code:
       0: iload_1
       1: istore_3
       2: iconst_1
       3: iload_3
       4: if_icmpne     22
       7: getstatic     #25                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      10: ldc           #27                 // String true..
      12: invokevirtual #31                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      15: getstatic     #37                 // Field scala/runtime/BoxedUnit.UNIT:Lscala/runtime/BoxedUnit;
      18: astore_2
      19: goto          60
      22: goto          25
      25: iconst_0
      26: iload_3
      27: if_icmpne     45
      30: getstatic     #25                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      33: ldc           #39                 // String false...
      35: invokevirtual #31                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      38: getstatic     #37                 // Field scala/runtime/BoxedUnit.UNIT:Lscala/runtime/BoxedUnit;
      41: astore_2
      42: goto          60
      45: goto          48
      48: new           #41                 // class scala/MatchError
      51: dup
      52: iload_3
      53: invokestatic  #47                 // Method scala/runtime/BoxesRunTime.boxToBoolean:(Z)Ljava/lang/Boolean;
      56: invokespecial #49                 // Method scala/MatchError."<init>":(Ljava/lang/Object;)V
      59: athrow
      60: return

  public $line4.$read$$iw$$iw$();
    Code:
       0: aload_0
       1: invokespecial #52                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: putstatic     #54                 // Field MODULE$:L$line4/$read$$iw$$iw$;
       8: return
}

 

 当我使用if表达式做同样的事情时，有不同的字节码。 
 

scala> def compareAgain(flag: Boolean) = {
     | if(flag) println("true..")
     | else println("false...")
     | }
compareAgain: (flag: Boolean)Unit

scala> :javap -c compareAgain
Compiled from "<console>"
public class $line5.$read$$iw$$iw$ {
  public static $line5.$read$$iw$$iw$ MODULE$;

  public static {};
    Code:
       0: new           #2                  // class $line5/$read$$iw$$iw$
       3: invokespecial #17                 // Method "<init>":()V
       6: return

  public void compareAgain(boolean);
    Code:
       0: iload_1
       1: ifeq          15
       4: getstatic     #25                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
       7: ldc           #27                 // String true..
       9: invokevirtual #31                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      12: goto          23
      15: getstatic     #25                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      18: ldc           #33                 // String false...
      20: invokevirtual #31                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      23: return

  public $line5.$read$$iw$$iw$();
    Code:
       0: aload_0
       1: invokespecial #36                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: putstatic     #38                 // Field MODULE$:L$line5/$read$$iw$$iw$;
       8: return
}

 

 有不同的字节码。 这在第一个字节码中意味着什么？ 
 

// Field scala/runtime/BoxedUnit.UNIT:Lscala/runtime/BoxedUnit;

 

 提前致谢。 

I am trying to do a pattern match on the boolean value. I have written the same method with a slight modification but there is much difference in their bytecode generation.
 

For example
 

scala> def compare(flag: Boolean) = {
     | flag match{
     | case true => println("true..")
     | case false => println("false...")
     | }}
compare: (flag: Boolean)Unit

scala> :javap -c compare
Compiled from "<console>"
public class $line4.$read$$iw$$iw$ {
  public static $line4.$read$$iw$$iw$ MODULE$;

  public static {};
    Code:
       0: new           #2                  // class $line4/$read$$iw$$iw$
       3: invokespecial #17                 // Method "<init>":()V
       6: return

  public void compare(boolean);
    Code:
       0: iload_1
       1: istore_3
       2: iconst_1
       3: iload_3
       4: if_icmpne     22
       7: getstatic     #25                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      10: ldc           #27                 // String true..
      12: invokevirtual #31                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      15: getstatic     #37                 // Field scala/runtime/BoxedUnit.UNIT:Lscala/runtime/BoxedUnit;
      18: astore_2
      19: goto          60
      22: goto          25
      25: iconst_0
      26: iload_3
      27: if_icmpne     45
      30: getstatic     #25                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      33: ldc           #39                 // String false...
      35: invokevirtual #31                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      38: getstatic     #37                 // Field scala/runtime/BoxedUnit.UNIT:Lscala/runtime/BoxedUnit;
      41: astore_2
      42: goto          60
      45: goto          48
      48: new           #41                 // class scala/MatchError
      51: dup
      52: iload_3
      53: invokestatic  #47                 // Method scala/runtime/BoxesRunTime.boxToBoolean:(Z)Ljava/lang/Boolean;
      56: invokespecial #49                 // Method scala/MatchError."<init>":(Ljava/lang/Object;)V
      59: athrow
      60: return

  public $line4.$read$$iw$$iw$();
    Code:
       0: aload_0
       1: invokespecial #52                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: putstatic     #54                 // Field MODULE$:L$line4/$read$$iw$$iw$;
       8: return
}

 

When I do the same thing using if expression, there is different bytecode.
 

scala> def compareAgain(flag: Boolean) = {
     | if(flag) println("true..")
     | else println("false...")
     | }
compareAgain: (flag: Boolean)Unit

scala> :javap -c compareAgain
Compiled from "<console>"
public class $line5.$read$$iw$$iw$ {
  public static $line5.$read$$iw$$iw$ MODULE$;

  public static {};
    Code:
       0: new           #2                  // class $line5/$read$$iw$$iw$
       3: invokespecial #17                 // Method "<init>":()V
       6: return

  public void compareAgain(boolean);
    Code:
       0: iload_1
       1: ifeq          15
       4: getstatic     #25                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
       7: ldc           #27                 // String true..
       9: invokevirtual #31                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      12: goto          23
      15: getstatic     #25                 // Field scala/Predef$.MODULE$:Lscala/Predef$;
      18: ldc           #33                 // String false...
      20: invokevirtual #31                 // Method scala/Predef$.println:(Ljava/lang/Object;)V
      23: return

  public $line5.$read$$iw$$iw$();
    Code:
       0: aload_0
       1: invokespecial #36                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: putstatic     #38                 // Field MODULE$:L$line5/$read$$iw$$iw$;
       8: return
}

 

There is different bytecode. What does this mean in first bytecode?
 

// Field scala/runtime/BoxedUnit.UNIT:Lscala/runtime/BoxedUnit;

 

Thanks in advance.

原文：https://stackoverflow.com/questions/50510305
更新时间：2023-06-11 17:06

最满意答案

 您的小数分隔符有问题（默认情况下，R假定为. ）。 最简单的解决方案可能只是将逗号转换为句点（句号） 
 

testDat <- c("0,123","2,13","na")
as.double(gsub(",",".",testDat))

 

 由于数据集中的"na"值，您仍会收到一些警告; 您可以通过单独转换"na"值来避免警告，如下所示： 
 

NAvals <- testDat=="na"
res <- numeric(length(testDat))
res[NAvals] <- NA
res[!NAvals] <- as.double(gsub(",",".",testDat[!NAvals]))

 

 可能还有一些方法可以重置您的语言环境（ ?Sys.setlocale ），以便它自动运行，但我无法弄明白。 
 

 这是另一种方法： 
 

scan(text=testDat,dec=",",na.strings="na",quiet=TRUE)


You have a problem with your decimal separators (R assumes . by default). The simplest solution is probably just to convert commas to periods (full stops)
 

testDat <- c("0,123","2,13","na")
as.double(gsub(",",".",testDat))

 

You will still get some warnings due to the "na" values in your data set; you could avoid the warnings by converting the "na" values separately, as follows:
 

NAvals <- testDat=="na"
res <- numeric(length(testDat))
res[NAvals] <- NA
res[!NAvals] <- as.double(gsub(",",".",testDat[!NAvals]))

 

There may also be some way to reset your locale (?Sys.setlocale) so that it works automatically, but I haven't been able to figure it out.
 

Here's another way to do it:
 

scan(text=testDat,dec=",",na.strings="na",quiet=TRUE)

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