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I created a hierarchy of case objects in Scala that looks like the following:
package my.awesome.package sealed abstract class PresetShapeType(val displayName: String) case object AccelerationSensor extends PresetShapeType("Acceleration Sensor") case object DisplacementSensor extends PresetShapeType("Displacement Sensor") case object ForceSensor extends PresetShapeType("Force Sensor") case object PressureSensor extends PresetShapeType("Pressure Sensor") case object StrainSensor extends PresetShapeType("Strain Sensor") I also have a piece of Java code in which I'd like to access PressureSensor, but the following does not work:
package my.awesome.package.subpackage; import my.awesome.package.PressureSensor; // Do some stuff, then... DVShape newshape = DVShapeFactory.createPresetShape(PressureSensor, new Point3f(0,0,0)); So, how do I reference the PressureSensor case object from Java? I decompiled the byte code for both the PressureSensor and PressureSensor$ classes, which yielded the following:
Compiled from "DVShapeFactory.scala" public final class org.nees.rpi.vis.PressureSensor extends java.lang.Object{ public static final java.lang.Object productElement(int); public static final int productArity(); public static final java.lang.String productPrefix(); public static final int $tag(); public static final java.lang.String displayName(); } Compiled from "DVShapeFactory.scala" public final class org.nees.rpi.vis.PressureSensor$ extends org.nees.rpi.vis.PresetShapeType implements scala.ScalaObject,scala.Product,java.io.Serializable{ public static final org.nees.rpi.vis.PressureSensor$ MODULE$; public static {}; public org.nees.rpi.vis.PressureSensor$(); public java.lang.Object readResolve(); public java.lang.Object productElement(int); public int productArity(); public java.lang.String productPrefix(); public final java.lang.String toString(); public int $tag(); } But that didn't yield any great insight.
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A case object is like an object , but just like a case class has more features than a regular class, a case object has more features than a regular object. Its features include: It's serializable. It has a default hashCode implementation. It has an improved toString implementation.
A case class can take arguments, so each instance of that case class can be different based on the values of it's arguments. A case object on the other hand does not take args in the constructor, so there can only be one instance of it (a singleton, like a regular scala object is).
case _ => does not check for the type, so it would match anything (similar to default in Java). case _ : ByteType matches only an instance of ByteType . It is the same like case x : ByteType , just without binding the casted matched object to a name x .
from Java, say:
my.awesome.package.PressureSensor$.MODULE$ PressureSensor$.MODULE$ should give you the instance of the case object.
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