Package Summary  Overview Summary

class:Comparator [NONE]
  • Type Parameters:
    T - the type of objects that may be compared by this comparator
    All Known Implementing Classes:
    Collator, RuleBasedCollator
    Functional Interface:
    This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference. 

    @FunctionalInterface
public interface Comparator<T>
    A comparison function, which imposes a total ordering on some collection of objects. Comparators can be passed to a sort method (such as Collections.sort or Arrays.sort) to allow precise control over the sort order. Comparators can also be used to control the order of certain data structures (such as sorted sets or sorted maps ), or to provide an ordering for collections of objects that don't have a natural ordering .

    The ordering imposed by a comparator c on a set of elements S is said to be consistent with equals if and only if c.compare(e1, e2)==0 has the same boolean value as e1.equals(e2) for every e1 and e2 in S.

    Caution should be exercised when using a comparator capable of imposing an ordering inconsistent with equals to order a sorted set (or sorted map). Suppose a sorted set (or sorted map) with an explicit comparator c is used with elements (or keys) drawn from a set S. If the ordering imposed by c on S is inconsistent with equals, the sorted set (or sorted map) will behave "strangely." In particular the sorted set (or sorted map) will violate the general contract for set (or map), which is defined in terms of equals.

    For example, suppose one adds two elements a and b such that (a.equals(b) && c.compare(a, b) != 0) to an empty TreeSet with comparator c. The second add operation will return true (and the size of the tree set will increase) because a and b are not equivalent from the tree set's perspective, even though this is contrary to the specification of the Set.add method.

    Note: It is generally a good idea for comparators to also implement java.io.Serializable, as they may be used as ordering methods in serializable data structures (like TreeSet, TreeMap). In order for the data structure to serialize successfully, the comparator (if provided) must implement Serializable.

    For the mathematically inclined, the relation that defines the imposed ordering that a given comparator c imposes on a given set of objects S is:

           {(x, y) such that c.compare(x, y) <= 0}.
    The quotient for this total order is:
           {(x, y) such that c.compare(x, y) == 0}.
    It follows immediately from the contract for compare that the quotient is an equivalence relation on S, and that the imposed ordering is a total order on S. When we say that the ordering imposed by c on S is consistent with equals , we mean that the quotient for the ordering is the equivalence relation defined by the objects' equals(Object) method(s):
         {(x, y) such that x.equals(y)}.

    Unlike Comparable, a comparator may optionally permit comparison of null arguments, while maintaining the requirements for an equivalence relation.

    This interface is a member of the Java Collections Framework .

    Since:
    1.2
    See Also:
    Comparable, Serializable

method:equals(java.lang.Object) [NONE]

  • equals

    boolean equals(Object obj)
    Indicates whether some other object is "equal to" this comparator. This method must obey the general contract of Object.equals(Object). Additionally, this method can return trueonly if the specified object is also a comparator and it imposes the same ordering as this comparator. Thus, comp1.equals(comp2) implies that sgn(comp1.compare(o1, o2))==sgn(comp2.compare(o1, o2)) for every object reference o1 and o2.

    Note that it is always safe not to override Object.equals(Object). However, overriding this method may, in some cases, improve performance by allowing programs to determine that two distinct comparators impose the same order.

    Overrides:
    equals in class Object
    Parameters:
    obj - the reference object with which to compare.
    Returns:
    true only if the specified object is also a comparator and it imposes the same ordering as this comparator.
    See Also:
    Object.equals(Object), Object.hashCode()

method:thenComparing(java.util.Comparator) [CHANGED]

  • thenComparing

    default Comparator<T> thenComparing(Comparator<? super T> other)
    Constructs a lexicographic order comparator with another comparator. For example,If this Comparator considers two elements equal, i.e. compare(a, b) == 0 , other is used to determine the order.

    The returned comparator is serializable if the specified comparator is also serializable.

    API Note:
    To sort a Comparator<Person> byLastName collection of String based on the length and then case-insensitive natural ordering, the comparator can be composed with another Comparator<Person> byFirstName , thenbyLastNameconstrucred using following code, 
    
     Comparator<String> cmp = Comparator.comparing(String::length)
             .thenComparing(byFirstName)createsaComparator<Person>whichsortsbylastname,andforequallastnamessortsbyfirstname.String.CASE_INSENSITIVE_ORDER);
    Parameters:
    other - the other comparator to be used when equals onthis comparator compares two objects that are equal.
    Returns:
    A lexicographic order comparator composed of this .and then the other comparator
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8

  • thenComparing

    default Comparator<T> thenComparing(Comparator<? super T> other)
    Constructs a lexicographic order comparator with another comparator. For example, a Comparator<Person> byLastName can be composed with another Comparator<Person> byFirstName , then byLastName.thenComparing(byFirstName) creates a Comparator<Person> which sorts by last name, and for equal last names sorts by first name.
    Parameters:
    other - the other comparator used when equals on this.
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8

  • thenComparing

    default Comparator<T> thenComparing(Comparator<? super T> other)
    Constructs a lexicographic order comparator with another comparator. If this Comparator considers two elements equal, i.e. compare(a, b) == 0 , other is used to determine the order.

    The returned comparator is serializable if the specified comparator is also serializable.

    API Note:
    To sort a collection of String based on the length and then case-insensitive natural ordering, the comparator can be construcred using following code,
    
     Comparator<String> cmp = Comparator.comparing(String::length)
             .thenComparing(String.CASE_INSENSITIVE_ORDER);
    Parameters:
    other - the other comparator to be used when this comparator compares two objects that are equal.
    Returns:
    A lexicographic order comparator composed of this and then the other comparator
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8

method:thenComparing(java.util.function.Function) [CHANGED]

  • thenComparing

    default <U extends Comparable<? super U>> Comparator<T> thenComparing(Function<? super T,? extends U> keyExtractor)
    Constructs a lexicographic order comparator with a function that extracts a Comparable sort key.
    Implementation Requirements:
    This default implementation calls thenComparing(this, Comparators.comparing(keyExtractor)) .
    Type Parameters:
    U - The type of the Comparable type for comparisonsort key
    Parameters:
    keyExtractor - the function used to extract the Comparable sort key
    Returns:
    A lexicographic order comparator composed of this and then the Comparable sort key.
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    Comparators.comparing(Function), thenComparing(Comparator)

  • thenComparing

    default <U extends Comparable<? super U>> Comparator<T> thenComparing(Function<? super T,? extends U> keyExtractor)
    Constructs a lexicographic order comparator with a function that extracts a Comparable sort key.
    Implementation Requirements:
    This default implementation calls thenComparing(comparing(keyExtractor)).
    Type Parameters:
    U - The type of the Comparable sort key
    Parameters:
    keyExtractor - the function used to extract the Comparable sort key
    Returns:
    A lexicographic order comparator composed of this and then the Comparable sort key.
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    comparing(Function), thenComparing(Comparator)

method:thenComparing(java.util.function.ToIntFunction) [CHANGED]

  • thenComparing

    default Comparator<T> thenComparing(ToIntFunction<? super T> keyExtractor)
    Constructs a lexicographic order comparator with a function that extracts a int value.sort key.
    Implementation Requirements:
    This default implementation calls thenComparing(this, Comparators.comparing(keyExtractor)) .
    Parameters:
    keyExtractor - the function used to extract the integer valuesort key
    Returns:
    A lexicographic order comparator composed of this and then the int sort key
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    Comparators.comparing(ToIntFunction), thenComparing(Comparator)

  • thenComparing

    default Comparator<T> thenComparing(ToIntFunction<? super T> keyExtractor)
    Constructs a lexicographic order comparator with a function that extracts a int sort key.
    Implementation Requirements:
    This default implementation calls thenComparing(comparing(keyExtractor)).
    Parameters:
    keyExtractor - the function used to extract the integer sort key
    Returns:
    A lexicographic order comparator composed of this and then the int sort key
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    comparing(ToIntFunction), thenComparing(Comparator)

method:thenComparing(java.util.function.ToLongFunction) [CHANGED]

  • thenComparing

    default Comparator<T> thenComparing(ToLongFunction<? super T> keyExtractor)
    Constructs a lexicographic order comparator with a function that extracts a long value.sort key.
    Implementation Requirements:
    This default implementation calls thenComparing(this, Comparators.comparing(keyExtractor)) .
    Parameters:
    keyExtractor - the function used to extract the long sort key
    Returns:
    A lexicographic order comparator composed of this and then the long valuesort key
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    Comparators.comparing(ToLongFunction), thenComparing(Comparator)

  • thenComparing

    default Comparator<T> thenComparing(ToLongFunction<? super T> keyExtractor)
    Constructs a lexicographic order comparator with a function that extracts a long sort key.
    Implementation Requirements:
    This default implementation calls thenComparing(comparing(keyExtractor)).
    Parameters:
    keyExtractor - the function used to extract the long sort key
    Returns:
    A lexicographic order comparator composed of this and then the long sort key
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    comparing(ToLongFunction), thenComparing(Comparator)

method:thenComparing(java.util.function.ToDoubleFunction) [CHANGED]

  • thenComparing

    default Comparator<T> thenComparing(ToDoubleFunction<? super T> keyExtractor)
    Constructs a lexicographic order comparator with a function that extracts a double value.sort key.
    Implementation Requirements:
    This default implementation calls thenComparing(this, Comparators.comparing(keyExtractor)) .
    Parameters:
    keyExtractor - the function used to extract the double sort key
    Returns:
    A lexicographic order comparator composed of this and then the double valuesort key
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    Comparators.comparing(ToDoubleFunction), thenComparing(Comparator)

  • thenComparing

    default Comparator<T> thenComparing(ToDoubleFunction<? super T> keyExtractor)
    Constructs a lexicographic order comparator with a function that extracts a double sort key.
    Implementation Requirements:
    This default implementation calls thenComparing(comparing(keyExtractor)).
    Parameters:
    keyExtractor - the function used to extract the double sort key
    Returns:
    A lexicographic order comparator composed of this and then the double sort key
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    comparing(ToDoubleFunction), thenComparing(Comparator)

method:reverseOrder() [CHANGED]

  • reverseOrder

    default static <T extends Comparable<? super T>> Comparator<T> reverseOrder<T> reverseOrder()
    Returns a comparator that imposes the reverse of the natural ordering .

    The returned comparator is serializable and throws NullPointerException when comparing null.

    Type Parameters:
    T - The Comparable type of this comparator.element to be compared
    Returns:
    A comparator that imposes the reverse of the natural ordering on a collection of this comparatorobjects that implement the Comparable interface.
    Since:
    1.8
    See Also:
    Comparable

  • reverseOrder

    default Comparator<T> reverseOrder()
    Returns a comparator that imposes the reverse ordering of this comparator.
    Returns:
    A comparator that imposes the reverse ordering of this comparator.
    Since:
    1.8

  • reverseOrder

    static <T extends Comparable<? super T>> Comparator<T> reverseOrder()
    Returns a comparator that imposes the reverse of the natural ordering .

    The returned comparator is serializable and throws NullPointerException when comparing null.

    Type Parameters:
    T - The Comparable type of element to be compared
    Returns:
    A comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface.
    Since:
    1.8
    See Also:
    Comparable

method:reversed() [ADDED]

  • reversed 

    default Comparator<T> reversed()
    Returns a comparator that imposes the reverse ordering of this comparator.
    Returns:
    A comparator that imposes the reverse ordering of this comparator.
    Since:
    1.8

method:thenComparing(java.util.function.Function, java.util.Comparator) [ADDED]

  • thenComparing 

    default <U extends Comparable<? super U>> Comparator<T> thenComparing(Function<? super T,? extends U> keyExtractor,
                                                                      Comparator<? super U> keyComparator)
    Constructs a lexicographic order comparator with a function that extracts a key to be compared with the given Comparator.
    Implementation Requirements:
    This default implementation calls thenComparing(comparing(keyExtractor, cmp)) .
    Type Parameters:
    U - The type of the sort key
    Parameters:
    keyExtractor - the function used to extract the sort key
    keyComparator - the Comparator used to compare the sort key
    Returns:
    A lexicographic order comparator composed of this and then the key comparator.
    Throws:
    NullPointerException - if the argument is null.
    Since:
    1.8
    See Also:
    comparing(Function, Comparator) , thenComparing(Comparator)

method:naturalOrder() [ADDED]

  • naturalOrder 

    static <T extends Comparable<? super T>> Comparator<T> naturalOrder()
    Returns a comparator compares Comparable type in natural order.

    The returned comparator is serializable and throws NullPointerException when comparing null.

    Type Parameters:
    T - The Comparable type of element to be compared
    Returns:
    A comparator that imposes the natural ordering on a collection of objects that implement the Comparable interface.
    Since:
    1.8
    See Also:
    Comparable

method:nullsFirst(java.util.Comparator) [ADDED]

  • nullsFirst 

    static <T> Comparator<T> nullsFirst(Comparator<? super T> comparator)
    Returns a null-friendly comparator that considers null to be less than non-null. When both are null, they are considered equal. If both are non-null, the specified Comparator is used to determine the order.

    The returned comparator is serializable if the specified comparator is serializable.

    Type Parameters:
    T - the type of the elements to be compared
    Parameters:
    comparator - A Comparator for comparing non-null values
    Returns:
    A comparator that considers null to be less than non-null.
    Since:
    1.8

method:nullsLast(java.util.Comparator) [ADDED]

  • nullsLast 

    static <T> Comparator<T> nullsLast(Comparator<? super T> comparator)
    Returns a null-friendly comparator that considers null to be greater than non-null. When both are null, they are considered equal. If both are non-null, the specified Comparator is used to determine the order.

    The returned comparator is serializable if the specified comparator is serializable.

    Type Parameters:
    T - the type of the elements to be compared
    Parameters:
    comparator - A Comparator for comparing non-null values
    Returns:
    A comparator that considers null to be greater than non-null.
    Since:
    1.8

method:comparing(java.util.function.Function, java.util.Comparator) [ADDED]

  • comparing 

    static <T,U> Comparator<T> comparing(Function<? super T,? extends U> keyExtractor,
                                     Comparator<? super U> keyComparator)
    Accepts a function that extracts a sort key from a type T, and returns a Comparator<T> that compares by that sort key using the specified Comparator.

    The returned comparator is serializable if the specified function and comparator are both serializable.

    API Note:
    To obtain a Comparator that compares Person objects by their last name ignoring case differences, 
    
     Comparator<People> cmp = Comparator.comparing(
             Person::getLastName,
             String.CASE_INSENSITIVE_ORDER);
    Type Parameters:
    T - The type of element to be compared
    U - The type of the sort key
    Parameters:
    keyExtractor - the function used to extract the sort key
    keyComparator - the Comparator used to compare the sort key
    Returns:
    A comparator that compares by an extracted key using the specified Comparator
    Throws:
    NullPointerException - if the argument is null
    Since:
    1.8

method:comparing(java.util.function.Function) [ADDED]

  • comparing 

    static <T,U extends Comparable<? super U>> Comparator<T> comparing(Function<? super T,? extends U> keyExtractor)
    Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator<T> that compares by that sort key.

    The returned comparator is serializable if the specified function is also serializable.

    API Note:
    To obtain a Comparator that compares Person objects by their last name, 
    
     Comparator<People> byLastName = Comparator.comparing(Person::getLastName);
    Type Parameters:
    T - The type of element to be compared
    U - The type of the Comparable sort key
    Parameters:
    keyExtractor - the function used to extract the Comparable sort key
    Returns:
    A comparator that compares by an extracted key
    Throws:
    NullPointerException - if the argument is null
    Since:
    1.8

method:comparing(java.util.function.ToIntFunction) [ADDED]

  • comparing 

    static <T> Comparator<T> comparing(ToIntFunction<? super T> keyExtractor)
    Accepts a function that extracts an int sort key from a type T, and returns a Comparator<T> that compares by that sort key.

    The returned comparator is serializable if the specified function is also serializable.

    Type Parameters:
    T - The type of element to be compared
    Parameters:
    keyExtractor - the function used to extract the integer sort key
    Returns:
    A comparator that compares by an extracted key
    Throws:
    NullPointerException - if the argument is null
    Since:
    1.8
    See Also:
    comparing(Function)

method:comparing(java.util.function.ToLongFunction) [ADDED]

  • comparing 

    static <T> Comparator<T> comparing(ToLongFunction<? super T> keyExtractor)
    Accepts a function that extracts a long sort key from a type T, and returns a Comparator<T> that compares by that sort key.

    The returned comparator is serializable if the specified function is also serializable.

    Type Parameters:
    T - The type of element to be compared
    Parameters:
    keyExtractor - the function used to extract the long sort key
    Returns:
    A comparator that compares by an extracted key
    Throws:
    NullPointerException - if the argument is null
    Since:
    1.8
    See Also:
    comparing(Function)

method:comparing(java.util.function.ToDoubleFunction) [ADDED]

  • comparing 

    static <T> Comparator<T> comparing(ToDoubleFunction<? super T> keyExtractor)
    Accepts a function that extracts a double sort key from a type T, and returns a Comparator<T> that compares by that sort key.

    The returned comparator is serializable if the specified function is also serializable.

    Type Parameters:
    T - The type of element to be compared
    Parameters:
    keyExtractor - the function used to extract the double sort key
    Returns:
    A comparator that compares by an extracted key
    Throws:
    NullPointerException - if the argument is null
    Since:
    1.8
    See Also:
    comparing(Function)