Interface Comparators

public interface Comparators
Some utilities to make comparisons easier to do, especially with null handling

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    COMPARISON_REQUIRED
    When you compare, the nulls can be quite annoying to handle.

  • Method Summary

    Static Methods
    Modifier and Type
    Method
    Description
    static <T> int
    compare(T a, T b)
    Compare two objects.
    static <T> int
    compare(T a, T b, int maxDepth)
    Compare two objects.
    static <T> int
    compare(T a, T b, Comparator<T> nonNullComparator)
    Protect a comparator from being called with null if they are both null, 0 if a and !b -> 1 if !a and b -> -1 Otherwise result of the nonNulComparator.compare(a,b)
    static <T> int
    compare(T a, T b, IntSupplier nonNullComparator)
    Shield the nonNullComparator from null objects.
    static int
    compareMapsByKeys(Map<String,Object> a, Map<String,Object> b, String... keys)
    Compare sequential fields in a Map with compare(Object, Object).
    static <T> int
    comparePresent(T a, T b)
    Compare two objects for null.
    static <T> int
    comparePresentEquals(T a, T b)
    Compare two objects for null and equality.
    static boolean
    isFinal(int compare)
    Check if compare value is final, that it decides the comparison and can be used as return value in a compare operation.

  • Field Details

    • COMPARISON_REQUIRED

      static final int COMPARISON_REQUIRED
      When you compare, the nulls can be quite annoying to handle. For this interface, we use a magic value to mark outside the normal 1,0,-1 values for compare to indicate that both values are not null and should be compared with traditional means.
      See Also:

  • Method Details

    • compare

      static <T> int compare(T a, T b, Comparator<T> nonNullComparator)
      Protect a comparator from being called with null
      • if they are both null, 0
      • if a and !b -> 1
      • if !a and b -> -1
      • Otherwise result of the nonNulComparator.compare(a,b)
      Type Parameters:
      T - the shared type
      Parameters:
      a -
      b -
      nonNullComparator -
      Returns:
      the result

    • compare

      static <T> int compare(T a, T b, IntSupplier nonNullComparator)
      Shield the nonNullComparator from null objects. This is a convenience method so you do not have to invent new parameter names but can use the direct parameters from the invoked method.
      • if they are both null, 0
      • if a and !b -> 1
      • if !a and b -> -1
      • Otherwise nonNullComparator.getAsInt()
      Type Parameters:
      T - the shared type
      Parameters:
      a -
      b -
      Returns:
      the result

    • comparePresent

      static <T> int comparePresent(T a, T b)
      Compare two objects for null.
      • if they are both null, 0
      • if a and !b -> 1
      • if !a and b -> -1
      • Otherwise Integer.MAXVALUE

      To use this, compare the result with invalid input: '<'=1 and return if so.

      Type Parameters:
      T - the shared type
      Parameters:
      a -
      b -
      Returns:
      the result

    • comparePresentEquals

      static <T> int comparePresentEquals(T a, T b)
      Compare two objects for null and equality.
      • if they are both null, 0
      • if a and !b -> 1
      • if !a and b -> -1
      • if a.equals(b) -> 0
      • Otherwise Integer.MAXVALUE

      To use this, compare the result with invalid input: '<'=1 and return if so.

      Type Parameters:
      T - the shared type
      Parameters:
      a -
      b -
      Returns:
      the result

    • isFinal

      static boolean isFinal(int compare)
      Check if compare value is final, that it decides the comparison and can be used as return value in a compare operation.

    • compare

      static <T> int compare(T a, T b)
      Compare two objects.
      • Test for null as in comparePresent(Object, Object)
      • Test for same class, if not class names are compared
      • Test if they are comparable, use the object comparison
      • If array, compare the fields of the array with this method in order, if all match, the longer is higher.
      • If Collection, compare the members of the Collection with this method in order, longer is higher
      • returns 0 in a desperate attempt. This can make objects return 0 that are not equals.
      The method compares to a depth of 4
      Type Parameters:
      T - the shared type of the objects
      Parameters:
      a -
      b -
      Returns:
      0, 1 a>b, -1 ainvalid input: '<'b

    • compare

      static <T> int compare(T a, T b, int maxDepth)
      Compare two objects.
      • Test for null as in comparePresent(Object, Object)
      • Test for same class, if not class names are compared
      • Test if they are comparable, use the object comparison
      • If array, compare the fields of the array with this method in order, if all match, the longer is higher.
      • If Collection, compare the members of the Collection with this method in order, longer is higher
      • returns 0 in a desperate attempt. This can make objects return 0 that are not equals.
      The method compares to a depth of 4
      Type Parameters:
      T - the shared type of the objects
      Parameters:
      a -
      b -
      maxDepth - max number of recursions
      Returns:
      0, 1 a>b, -1 ainvalid input: '<'b

    • compareMapsByKeys

      static int compareMapsByKeys(Map<String,Object> a, Map<String,Object> b, String... keys)
      Compare sequential fields in a Map with compare(Object, Object). The given fields are retrieved from the map and then compared. The first non-0 value defines the result. If no keys are given, all keys in both maps in sorted order are used instead.
      Parameters:
      a - the a value or null
      b - the b value or null
      keys - the array of keys to use
      Returns:
      0, 1 a>b, -1 ainvalid input: '<'b