Module org.apache.sis.util
Package org.apache.sis.math

Enum Class FunctionProperty

Object
Enum<FunctionProperty>
FunctionProperty
All Implemented Interfaces:
Serializable, Comparable<Function­Property>, Constable
public enum FunctionProperty extends Enum<FunctionProperty>
The manners in which the inputs of a function are mapped to the outputs. The function doesn't need to be mathematical. For example, this enumeration can be used with Object­Converter.

Any given function can have zero, one or more properties from this enumeration. Some properties not included in this enumeration can be expressed by a combination of other properties:

Inferred function properties
Property How to build
Bijective EnumSet.of(INJECTIVE, SURJECTIVE)
Monotonic EnumSet.of(INJECTIVE) or Enum­Set​.of(SURJECTIVE)
Strictly increasing EnumSet.of(ORDER_PRESERVING, INJECTIVE)
Strictly decreasing EnumSet.of(ORDER_REVERSING, INJECTIVE)
Constant EnumSet.of(ORDER_PRESERVING, ORDER_REVERSING)
The Javadoc in this class uses the following terms:
  • S (as in source) is the set of all possible input values (the domain).
  • T (as in target) is a set containing all possible output values, and potentially more elements (the codomain). For example, the set of output values of the Integer​.to­String() function is included in a larger set, which is the set of all possible String values. In this Javadoc, T stands for the latter set.
Since:
0.3
See Also:

  • Enum Constant Details

    • INVERTIBLE

      public static final FunctionProperty INVERTIBLE
      A function is invertible if it can provide another function mapping T values to S values.

      While other values defined in this enumeration are more about the mathematical aspects of functions, this particular value is more about the programmatical aspect. A function may be conceptually invertible (all bijective functions should be), but the inverse operation may not be implemented. In such case, the function properties shall not include this INVERTIBLE value.

      See Also:

    • INJECTIVE

      public static final FunctionProperty INJECTIVE
      A function is injective if each value of T is either unrelated to S, or is the output of exactly one value of S. For example an Object­Converter doing conversions from Integer to String is an injective function, because no pair of integers can produce the same string.

      A function which is both injective and surjective is a bijective function. In such functions, there is a one-to-one relationship between all input and output values.

      See Also:

    • SURJECTIVE

      public static final FunctionProperty SURJECTIVE
      A function is surjective if any value of T can be created from one or many values of S. For example an Object­Converter doing conversions from String to Integer is a surjective function, because there is always at least one string for each integer value. Note that such function cannot be injective since many different strings can represent the same integer value.

      A function which is both injective and surjective is a bijective function. In such functions, there is a one-to-one relationship between all input and output values.

      See Also:

    • ORDER_PRESERVING

      public static final FunctionProperty ORDER_PRESERVING
      A function preserves order if any sequence of increasing S values is mapped to a sequence of increasing T values. This enumeration constant can be used only with Comparable types or primitive types having a comparable wrapper.

      Strictly ordered input values are not necessarily mapped to strictly ordered output values. Strictness is preserved only if the function is also injective.

      A function may be both order preserving and order reversing if all input values are mapped to a constant output value.

      See Also:

    • ORDER_REVERSING

      public static final FunctionProperty ORDER_REVERSING
      A function reverses order if any sequence of increasing S values is mapped to a sequence of decreasing T values. This enumeration constant can be used only with Comparable types or primitive types having a comparable wrapper.

      Strictly ordered input values are not necessarily mapped to strictly ordered output values. Strictness is preserved only if the function is also injective.

      A function may be both order preserving and order reversing if all input values are mapped to a constant output value.

      See Also:

    • VOLATILE

      public static final FunctionProperty VOLATILE
      A function is volatile if the computed value changes each time that the function is evaluated. It may be for example a random number generator, or a function returning the current date and time.
      Since:
      1.4

  • Method Details

    • values

      public static FunctionProperty[] values()
      Returns an array containing the constants of this enum class, in the order they are declared.
      Returns:
      an array containing the constants of this enum class, in the order they are declared

    • valueOf

      public static FunctionProperty valueOf(String name)
      Returns the enum constant of this class with the specified name. The string must match exactly an identifier used to declare an enum constant in this class. (Extraneous whitespace characters are not permitted.)
      Parameters:
      name - the name of the enum constant to be returned.
      Returns:
      the enum constant with the specified name
      Throws:
      Illegal­Argument­Exception - if this enum class has no constant with the specified name
      Null­Pointer­Exception - if the argument is null

    • isBijective

      public static boolean isBijective(Set<FunctionProperty> properties)
      Returns true if a function having the given set of properties is bijective. Bijective functions have a one-to-one relationship between all input and output values. This convenience method tests if the given set contains all following properties:
      Parameters:
      properties - the properties of the function to test for bijectivity.
      Returns:
      true if a function having the given set of properties is bijective.

    • isMonotonic

      public static boolean isMonotonic(Set<FunctionProperty> properties)
      Returns true if a function having the given set of properties is monotonic. This convenience method tests if the given set contains at least one of the following properties:
      Parameters:
      properties - the properties of the function to test for monotonicity.
      Returns:
      true if a function having the given set of properties is monotonic.

    • isConstant

      public static boolean isConstant(Set<FunctionProperty> properties)
      Returns true if a function can only return a constant value. This convenience method tests if the given set contains all of the following properties:
      Parameters:
      properties - the properties of the function to test.
      Returns:
      true if the function can only return a constant value.
      Since:
      1.4

    • concatenate

      public static EnumSet<FunctionProperty> concatenate(Set<FunctionProperty> step1, Set<FunctionProperty> step2)
      Returns the properties of a function defined as the concatenation of two other functions. The presence of a property in the returned set is determined by combining the presence of the same property in the two steps using the following logical operations: The returned set is always a new instance and is modifiable, thus allowing the caller to customize the property set.
      Parameters:
      step1 - properties of the first function.
      step2 - properties of the second function.
      Returns:
      properties of the concatenated function as a new and modifiable set.
      Since:
      1.4