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如何从Java中“获取”Scala实例对象?

case-class scala

32

mipadi · 技术社区 · 16 年前

我在scala中创建了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")

我还有一段Java代码,我想访问它。 PressureSensor ,但以下内容不起作用:

package my.awesome.package.subpackage;

import my.awesome.package.PressureSensor;

// Do some stuff, then...

DVShape newshape = DVShapeFactory.createPresetShape(PressureSensor, new Point3f(0,0,0));

那么,我如何引用 压力传感器 来自Java的实例对象?我为两个 压力传感器 和 PressureSensor$ 类,生成以下内容:

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();
}

但这并没有产生任何深刻的见解。

3 回复 | 直到 13 年前

1

35

Tomasz Nurkiewicz 13 年前

从Java,说:

my.awesome.package.PressureSensor$.MODULE$

2

10

Geoff Reedy 16 年前

PressureSensor$.MODULE$ 应该提供case对象的实例。

3

6

metasim 13 年前

这仍然是一个黑客,但在我看来,在Java中更可读。只需添加一个方法来显式返回对singleton实例的引用(它在类上显示为静态方法):

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 }

然后在Java中:

import my.awesome.package.PressureSensor;
DVShape newshape = DVShapeFactory.createPresetShape(PressureSensor.instance(), new Point3f(0,0,0));