我在玩https://kotlin.github.io/dataframe/overview.html，想看看从Java而不是Kotlin调用看起来有多复杂。我发现很多地方都有javap输出中显示的方法，例如：

$ javap -cp . org/jetbrains/kotlinx/dataframe/api/GroupByKt.class
Compiled from "groupBy.kt"
public final class org.jetbrains.kotlinx.dataframe.api.GroupByKt {
...
  public static org.jetbrains.kotlinx.dataframe.api.GroupBy groupBy$default(org.jetbrains.kotlinx.dataframe.DataFrame, boolean, kotlin.jvm.functions.Function2, int, java.lang.Object);
...

其中最后一个方法名为groupBy$default。在反编译Kotlin编译器生成的JVM字节码之后，我看到它调用了上面的函数。
但是，Eclipse会抱怨它是未定义的，并且无法编译Java类。Maven也抱怨道：

[ERROR] /prj/ks/KotlinxDataFrameTest.java:[130,21] cannot find symbol
  symbol:   method groupBy$default(org.jetbrains.kotlinx.dataframe.DataFrame<capture#1 of ?>,boolean,(gb,it)->[...] ""),int,<nulltype>)
  location: class org.jetbrains.kotlinx.dataframe.api.GroupByKt

我认为在javap中出现的任何方法都可以从Java中调用。我错过了什么？
编辑：根据@broot的评论添加了javap -verbose输出：

public static org.jetbrains.kotlinx.dataframe.api.GroupBy groupBy$default(org.jetbrains.kotlinx.dataframe.DataFrame, boolean, kotlin.jvm.functions.Function2, int, java.lang.Object);
    descriptor: (Lorg/jetbrains/kotlinx/dataframe/DataFrame;ZLkotlin/jvm/functions/Function2;ILjava/lang/Object;)Lorg/jetbrains/kotlinx/dataframe/api/GroupBy;
    flags: (0x1009) ACC_PUBLIC, ACC_STATIC, ACC_SYNTHETIC
    Code:
      stack=3, locals=5, args_size=5
         0: iload_3
         1: iconst_1
         2: iand
         3: ifeq          8
         6: iconst_1
         7: istore_1
         8: aload_0
         9: iload_1
        10: aload_2
        11: invokestatic  #32                 // Method groupBy:(Lorg/jetbrains/kotlinx/dataframe/DataFrame;ZLkotlin/jvm/functions/Function2;)Lorg/jetbrains/kotlinx/dataframe/api/GroupBy;
        14: areturn
      StackMapTable: number_of_entries = 1
        frame_type = 8 /* same */
      LineNumberTable:
        line 21: 0