Scala：Trait Companion对象在Java中不可见 [英] Scala: Trait Companion Object is not visible in Java

问题描述

Scala 中的特征的伴随对象在Scala中没有可见性问题 ：

trait ProtocolPacket extends Serializable {    
  def toByteArray: Array[Byte]
}

object ProtocolPacket {
  def getStreamType( streamBytes: Array[Byte] ) = {
    // ...
  }
}

但是在Java方面（例如在jar中获取上述内容）， ProtocolPacket.getStreamType 不可见。实际上，（由IDEA反编译）源没有为 ProtocolPacket

However on Java side (e.g. gets the above in a jar), a ProtocolPacket.getStreamType is not visible. In fact a (decompiled by IDEA) source does not have a getStreamType method defined for a ProtocolPacket

我在SO上找到类似的点击 Companion $ MODULE $ ，但被IDEA欺骗:)如下所示：

I found similar hits on SO regarding Companion$MODULE$, but was tricked by IDEA :) as shown below:

以上编译并运行正常（shell和/或IDEA本身），以防其他人被困。

The above compiles and runs fine (shell and/or IDEA itself), in case anybody else gets trapped.

推荐答案

查看 javap 输出，您会发现：

$ javap ProtocolPacket
public interface ProtocolPacket extends scala.Serializable{
    public abstract byte[] toByteArray();
}

和同伴对象：

$ javap ProtocolPacket$
public final class ProtocolPacket$ extends java.lang.Object implements scala.ScalaObject,scala.Serializable{
    public static final ProtocolPacket$ MODULE$;
    public static {};
    public void getStreamType(byte[]);
    public java.lang.Object readResolve();
}

这让我相信你可以写的Java：

this makes me believe in Java you can write:

ProtocolPacket$.MODULE$.getStreamType(/**/)

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