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11 Scala's Hierarchy

Sample run of chapter's interpreter examples

• 11.1 Scala's class hierarchy
• 11.2 How primitives are implemented
• 11.3 Bottom types
• 11.4 Conclusion

11.1 Scala's class hierarchy

  final def ==(that: Any): Boolean
  final def !=(that: Any): Boolean
  def equals(that: Any): Boolean
  def hashCode: Int
  def toString: String


  scala> new Int


  <console>:5: error: class Int is abstract; cannot be 
  instantiated
         new Int
         ^


  scala> 42.toString
  res1: java.lang.String = 42

  scala> 42.hashCode
  res2: Int = 42

  scala> 42 equals 42
  res3: Boolean = true


  scala> 42 max 43
  res4: Int = 43

  scala> 42 min 43
  res5: Int = 42

  scala> 1 until 5
  res6: Range = Range(1, 2, 3, 4)

  scala> 1 to 5
  res7: Range.Inclusive = Range(1, 2, 3, 4, 5)

  scala> 3.abs
  res8: Int = 3

  scala> (-3).abs
  res9: Int = 3


  

11.2 How primitives are implemented

// In file hierarchy/Ex1.java

  // This is Java
  boolean isEqual(int x, int y) {
    return x == y;
  }
  System.out.println(isEqual(421, 421));


// In file hierarchy/Ex2.java

  // This is Java
  boolean isEqual(Integer x, Integer y) {
    return x == y;
  }
  System.out.println(isEqual(421, 421));


  scala> def isEqual(x: Int, y: Int) = x == y
  isEqual: (Int,Int)Boolean

  scala> isEqual(421, 421)
  res10: Boolean = true

  scala> def isEqual(x: Any, y: Any) = x == y
  isEqual: (Any,Any)Boolean

  scala> isEqual(421, 421)
  res11: Boolean = true


  scala> val x = "abcd".substring(2)
  x: java.lang.String = cd

  scala> val y = "abcd".substring(2)
  y: java.lang.String = cd

  scala> x == y
  res12: Boolean = true


  scala> val x = new String("abc")
  x: java.lang.String = abc

  scala> val y = new String("abc")
  y: java.lang.String = abc

  scala> x == y
  res13: Boolean = true

  scala> x eq y
  res14: Boolean = false

  scala> x ne y
  res15: Boolean = true


  

11.3 Bottom types

  scala> val i: Int = null
  <console>:4: error: type mismatch;
   found   : Null(null)
   required: Int


  def error(message: String): Nothing =
    throw new RuntimeException(message)


// In file hierarchy/Ex3.scala

  def divide(x: Int, y: Int): Int = 
    if (y != 0) x / y 
    else error("can't divide by zero")


  

11.4 Conclusion