如何从 Java“获取”Scala case 对象？
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How do I "get" a Scala case object from Java?
提问by mipadi
I created a hierarchy of case objects in Scala that looks like the following:
我在 Scala 中创建了一个 case 对象的层次结构，如下所示：
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:
我还有一段 Java 代码，我想在其中访问PressureSensor，但以下不起作用：
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 PressureSensorcase object from Java? I decompiled the byte code for both the PressureSensorand PressureSensor$classes, which yielded the following:
那么，如何PressureSensor从 Java引用case 对象呢？我反编译了PressureSensor和PressureSensor$类的字节码，结果如下：
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 $tag();
}
But that didn't yield any great insight.
但这并没有产生任何深刻的见解。
回答by Seth Tisue
from Java, say:
来自 Java，说：
my.awesome.package.PressureSensor$.MODULE$
回答by Geoff Reedy
PressureSensor$.MODULE$should give you the instance of the case object.
PressureSensor$.MODULE$应该给你 case 对象的实例。
回答by metasim
This is still a hack, but in my opinion a bit more readable in Java. Just add a method to explicitly return the reference to the singleton instance (it shows up as a static method on the class):
这仍然是一个 hack，但在我看来，在 Java 中更具可读性。只需添加一个方法来显式返回对单例实例的引用（它显示为类上的静态方法）：
sealed abstract class PresetShapeType(val displayName: String)
case object AccelerationSensor extends PresetShapeType("Acceleration Sensor") { def instance = this }
case object DisplacementSensor extends PresetShapeType("Displacement Sensor") { def instance = this }
case object ForceSensor extends PresetShapeType("Force Sensor") { def instance = this }
case object PressureSensor extends PresetShapeType("Pressure Sensor") { def instance = this }
case object StrainSensor extends PresetShapeType("Strain Sensor") { def instance = this }
And then in Java:
然后在 Java 中：
import my.awesome.package.PressureSensor;
DVShape newshape = DVShapeFactory.createPresetShape(PressureSensor.instance(), new Point3f(0,0,0));
