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

Enum Class ComparisonMode

Object
Enum<ComparisonMode>
ComparisonMode
All Implemented Interfaces:
Serializable, Comparable<Comparison­Mode>, Constable
public enum ComparisonMode extends Enum<ComparisonMode>
Specifies the level of strictness when comparing two Lenient­Comparable objects for equality. This enumeration allows users to specify which kind of differences can be tolerated between two objects: differences in implementation class, differences in some kinds of property, or slight difference in numerical values.

This enumeration is ordered from stricter to more lenient levels:

  1. STRICT – All attributes of the compared objects shall be strictly equal.
  2. BY_CONTRACT – Only the attributes published in the interface contract need to be compared.
  3. IGNORE_METADATA – Only the attributes relevant to the object functionality are compared.
  4. APPROXIMATE – Only the attributes relevant to the object functionality are compared, with some tolerance threshold on numerical values.
  5. ALLOW_VARIANT – For objects not really equal but related (e.g. CRS using different axis order).
  6. DEBUG – Special mode for figuring out why two objects expected to be equal are not.
If two objects are equal at some level of strictness E, then they should also be equal at all levels listed below E in the above list. For example if two objects are equal at the BY_CONTRACT level, then they should also be equal at the IGNORE_METADATA level but not necessarily at the STRICT level.
Since:
0.3
See Also:

  • Enum Constant Details

    • STRICT

      public static final ComparisonMode STRICT
      All attributes of the compared objects shall be strictly equal. This comparison mode is equivalent to the Object​.equals(Object) method, and must be compliant with the contract documented in that method. In particular, this comparison mode shall be consistent with Object​.hash­Code() and be symmetric (A​.equals(B) implies B​.equals(A)).

      Implementation note

      In the SIS implementation, this comparison mode usually have the following characteristics (not always, this is only typical):
      • The objects being compared need to be the same implementation class.
      • Private fields are compared directly instead of invoking public getter methods.
      See Also:

    • BY_CONTRACT

      public static final ComparisonMode BY_CONTRACT
      Only the attributes published in some contract (typically a GeoAPI interface) need to be compared. The implementation classes do not need to be the same and some private attributes may be ignored.

      Note that this comparison mode does not guaranteed Object​.hash­Code() consistency, neither comparison symmetry (i.e. A​.equals(B) and B​.equals(A) may return different results if the equals methods are implemented differently).

      Implementation note

      In the SIS implementation, this comparison mode usually have the following characteristics (not always, this is only typical):
      • The objects being compared need to implement the same GeoAPI interfaces.
      • Public getter methods are used (no direct access to private fields).

    • IGNORE_METADATA

      public static final ComparisonMode IGNORE_METADATA
      Only the attributes relevant to the object functionality are compared. Attributes that are only informative can be ignored. This comparison mode is typically less strict than BY_CONTRACT.

      Application to coordinate reference systems

      If the objects being compared are Coordinate­Reference­System instances, then only the properties relevant to the coordinate localization shall be compared. Metadata like the identifiers or the domain of validity, which have no impact on the coordinates being calculated, shall be ignored.

      Application to coordinate operations

      If the objects being compared are Math­Transform instances, then two transforms defined in a different way may be considered equivalent. For example, it is possible to define a Mercator projection in different ways, named "variant A", "variant B" and "variant C" in EPSG dataset, each having their own set of parameters. The STRICT or BY_CONTRACT modes shall consider two projections as equal only if their parameter values are strictly identical, while the IGNORE_METADATA mode can consider those objects as equivalent despite difference in the set of parameters, as long as coordinate transformations still produce the same results.

      Example

      A "Mercator (variant B)" projection with a standard parallel value of 60° produces the same results than a "Mercator (variant A)" projection with a scale factor value of 0.5.
      See Also:

    • APPROXIMATE

      public static final ComparisonMode APPROXIMATE
      Only the attributes relevant to the object functionality are compared, with some tolerance threshold on numerical values.

      Application to coordinate operations

      If two Math­Transform objects are considered equal according this mode, then for any given identical source position, the two compared transforms shall compute at least approximately the same target position. A small difference is tolerated between the target coordinates calculated by the two math transforms. How small is “small” is implementation dependent — the threshold cannot be specified in the current implementation, because of the non-linear nature of map projections.
      Since:
      1.0

    • ALLOW_VARIANT

      public static final ComparisonMode ALLOW_VARIANT
      Most but not all attributes relevant to the object functionality are compared. This comparison mode is equivalent to APPROXIMATE, except that it ignores some attributes that may differ between objects not equal but related.

      The main purpose of this method is to verify if two Coordinate Reference Systems (CRS) are approximately equal ignoring axis order.

      Example

      Consider two geographic coordinate reference systems with the same attributes except axis order, where one CRS uses (latitude, longitude) axes and the other CRS uses (longitude, latitude) axes. All comparison modes (even APPROXIMATE) will consider those two CRS as different, except this ALLOW_VARIANT mode which will consider one CRS to be a variant of the other.
      Since:
      0.7

    • DEBUG

      @Debug public static final ComparisonMode DEBUG
      Same as APPROXIMATE, except that an Assertion­Error is thrown if the two objects are not equal and assertions are enabled. The exception message and stack trace help to locate which attributes are not equal. This mode is typically used in assertions like below: 
      assert Utilities.deepEquals(object1, object2, ComparisonMode.DEBUG);
      Note that a comparison in DEBUG mode may still return false without throwing an exception, since not all corner cases are tested. The exception is only intended to provide more details for some common cases.

  • Method Details

    • values

      public static ComparisonMode[] 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 ComparisonMode 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

    • isIgnoringMetadata

      public boolean isIgnoringMetadata()
      Returns true if this comparison ignores metadata. This method currently returns true for IGNORE_METADATA, APPROXIMATE or DEBUG only, but this list may be extended in future SIS versions.
      Returns:
      whether this comparison ignore metadata.
      Since:
      0.6

    • isApproximate

      public boolean isApproximate()
      Returns true if this comparison uses a tolerance threshold. This method currently returns true for APPROXIMATE or DEBUG only, but this list may be extended in future SIS versions.
      Returns:
      whether this comparison uses a tolerance threshold.
      Since:
      1.0

    • equalityLevel

      public static ComparisonMode equalityLevel(Object o1, Object o2)
      If the two given objects are equal according one of the modes enumerated in this class, then returns that mode. Otherwise returns null.

      Note: this method never return the DEBUG mode.

      Parameters:
      o1 - the first object to compare, or null.
      o2 - the second object to compare, or null.
      Returns:
      the most suitable comparison mode, or null if the two given objects are not equal according any mode in this enumeration.