等同于Scala中的公共静态最终字段

Question

我正在学习Scala，无法弄清楚如何在Scala中最好地表达这个简单的Java类：

public class Color {
  public static final Color BLACK = new Color(0, 0, 0);
  public static final Color WHITE = new Color(255, 255, 255);     
  public static final Color GREEN = new Color(0, 0, 255);

  private final int red;
  private final int blue;
  private final int green;

  public Color(int red, int blue, int green) {
    this.red = red;
    this.blue = blue;
    this.green = green;
  }

  // getters, et cetera
}

我所拥有的最好的是：

class Color(val red: Int, val blue: Int, val green: Int)
object BLACK extends Color(0, 0, 0)
object WHITE extends Color(255, 255, 255)
object GREEN extends Color(0, 0, 255)  

但是我失去了将BLACK，WHITE和GREEN绑定到Color名称空间的优点。

Answer 1

case class Color(red: Int, blue: Int, green: Int)

object Color {
  val BLACK = Color(0, 0, 0)
  val WHITE = Color(255, 255, 255)
  val GREEN = Color(0, 0, 255)
}

Answer 2

您可以将特定的颜色放入伴随对象中：

class Color(val red: Int, val blue: Int, val green: Int)
object Color {
  object BLACK extends Color(0, 0, 0)
  object WHITE extends Color(255, 255, 255)
  object GREEN extends Color(0, 0, 255)
}

---

编辑 ：

或者，您可以在随播对象中包含val：

class Color(val red: Int, val blue: Int, val green: Int)
object Color {
  val BLACK = new Color(0, 0, 0)
  val WHITE = new Color(255, 255, 255)
  val GREEN = new Color(0, 0, 255)
}

您可以让它们懒惰地推迟实例化，直到使用它们：

class Color(val red: Int, val blue: Int, val green: Int)
object Color {
  lazy val BLACK = new Color(0, 0, 0)
  lazy val WHITE = new Color(255, 255, 255)
  lazy val GREEN = new Color(0, 0, 255)
}

回到原始解决方案，您可以阻止类的扩展（通过将Color类密封来模拟“ final”：

sealed class Color(val red: Int, val blue: Int, val green: Int)
object Color {
  object BLACK extends Color(0, 0, 0)
  object WHITE extends Color(255, 255, 255)
  object GREEN extends Color(0, 0, 255)
}

Answer 3

密封允许对象扩展具有相同的物理文件..不在不同的文件中。 密封比最终包装更接近包装范围。