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comparatorjava用法

The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared.

Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. The returned comparator is serializable if the specified function is also serializable.

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 true only if the specified object is also a comparator and it imposes the same ordering as this comparator. Thus, comp1.equals(comp2) implies that signum(comp1.compare(o1, o2))==signum(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.

comparator中文

Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key.

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. If the specified comparator is null, then the returned comparator considers all non-null values to be equal. The returned comparator is serializable if the specified comparator is serializable.

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. If the specified comparator is null, then the returned comparator considers all non-null values to be equal. The returned comparator is serializable if the specified comparator is serializable.

Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key. The returned comparator is serializable if the specified function is also serializable.

Comparatorcircuit

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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)}. In other words, when the imposed ordering is consistent with equals, the equivalence classes defined by the equivalence relation of the equals method and the equivalence classes defined by the quotient of the compare method are the same. 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. See also: ComparableSerializable Summary Public methods abstract int compare(T o1, T o2) Compares its two arguments for order. static Comparator comparing(Function keyExtractor, Comparator keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator. static > Comparator comparing(Function keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingDouble(ToDoubleFunction keyExtractor) Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingInt(ToIntFunction keyExtractor) Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingLong(ToLongFunction keyExtractor) Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key. abstract boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. static > Comparator naturalOrder() Returns a comparator that compares Comparable objects in natural order. static Comparator nullsFirst(Comparator comparator) Returns a null-friendly comparator that considers null to be less than non-null. static Comparator nullsLast(Comparator comparator) Returns a null-friendly comparator that considers null to be greater than non-null. static > Comparator reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. default Comparator reversed() Returns a comparator that imposes the reverse ordering of this comparator. default > Comparator thenComparing(Function keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key. default Comparator thenComparing(Function keyExtractor, Comparator keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator. default Comparator thenComparing(Comparator other) Returns a lexicographic-order comparator with another comparator. default Comparator thenComparingDouble(ToDoubleFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a double sort key. default Comparator thenComparingInt(ToIntFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts an int sort key. default Comparator thenComparingLong(ToLongFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a long sort key. Public methods compare Added in API level 1 public abstract int compare (T o1, T o2) Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared. o2 T: the second object to be compared. Returns int a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. Throws NullPointerException if an argument is null and this comparator does not permit null arguments ClassCastException if the arguments' types prevent them from being compared by this comparator.

Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key. The returned comparator is serializable if the specified function is also serializable.

Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator. The returned comparator is serializable if the specified function and comparator are both serializable.

Java customcomparator

Returns 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.

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)}. In other words, when the imposed ordering is consistent with equals, the equivalence classes defined by the equivalence relation of the equals method and the equivalence classes defined by the quotient of the compare method are the same. 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. See also: ComparableSerializable Summary Public methods abstract int compare(T o1, T o2) Compares its two arguments for order. static Comparator comparing(Function keyExtractor, Comparator keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator. static > Comparator comparing(Function keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingDouble(ToDoubleFunction keyExtractor) Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingInt(ToIntFunction keyExtractor) Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingLong(ToLongFunction keyExtractor) Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key. abstract boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. static > Comparator naturalOrder() Returns a comparator that compares Comparable objects in natural order. static Comparator nullsFirst(Comparator comparator) Returns a null-friendly comparator that considers null to be less than non-null. static Comparator nullsLast(Comparator comparator) Returns a null-friendly comparator that considers null to be greater than non-null. static > Comparator reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. default Comparator reversed() Returns a comparator that imposes the reverse ordering of this comparator. default > Comparator thenComparing(Function keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key. default Comparator thenComparing(Function keyExtractor, Comparator keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator. default Comparator thenComparing(Comparator other) Returns a lexicographic-order comparator with another comparator. default Comparator thenComparingDouble(ToDoubleFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a double sort key. default Comparator thenComparingInt(ToIntFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts an int sort key. default Comparator thenComparingLong(ToLongFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a long sort key. Public methods compare Added in API level 1 public abstract int compare (T o1, T o2) Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared. o2 T: the second object to be compared. Returns int a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. Throws NullPointerException if an argument is null and this comparator does not permit null arguments ClassCastException if the arguments' types prevent them from being compared by this comparator.

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)}. In other words, when the imposed ordering is consistent with equals, the equivalence classes defined by the equivalence relation of the equals method and the equivalence classes defined by the quotient of the compare method are the same. 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. See also: ComparableSerializable Summary Public methods abstract int compare(T o1, T o2) Compares its two arguments for order. static Comparator comparing(Function keyExtractor, Comparator keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator. static > Comparator comparing(Function keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingDouble(ToDoubleFunction keyExtractor) Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingInt(ToIntFunction keyExtractor) Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingLong(ToLongFunction keyExtractor) Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key. abstract boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. static > Comparator naturalOrder() Returns a comparator that compares Comparable objects in natural order. static Comparator nullsFirst(Comparator comparator) Returns a null-friendly comparator that considers null to be less than non-null. static Comparator nullsLast(Comparator comparator) Returns a null-friendly comparator that considers null to be greater than non-null. static > Comparator reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. default Comparator reversed() Returns a comparator that imposes the reverse ordering of this comparator. default > Comparator thenComparing(Function keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key. default Comparator thenComparing(Function keyExtractor, Comparator keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator. default Comparator thenComparing(Comparator other) Returns a lexicographic-order comparator with another comparator. default Comparator thenComparingDouble(ToDoubleFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a double sort key. default Comparator thenComparingInt(ToIntFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts an int sort key. default Comparator thenComparingLong(ToLongFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a long sort key. Public methods compare Added in API level 1 public abstract int compare (T o1, T o2) Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared. o2 T: the second object to be compared. Returns int a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. Throws NullPointerException if an argument is null and this comparator does not permit null arguments ClassCastException if the arguments' types prevent them from being compared by this comparator.

Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key.

Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key. The returned comparator is serializable if the specified function is also serializable.

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. See also: ComparableSerializable Summary Public methods abstract int compare(T o1, T o2) Compares its two arguments for order. static Comparator comparing(Function keyExtractor, Comparator keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator. static > Comparator comparing(Function keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingDouble(ToDoubleFunction keyExtractor) Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingInt(ToIntFunction keyExtractor) Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingLong(ToLongFunction keyExtractor) Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key. abstract boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. static > Comparator naturalOrder() Returns a comparator that compares Comparable objects in natural order. static Comparator nullsFirst(Comparator comparator) Returns a null-friendly comparator that considers null to be less than non-null. static Comparator nullsLast(Comparator comparator) Returns a null-friendly comparator that considers null to be greater than non-null. static > Comparator reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. default Comparator reversed() Returns a comparator that imposes the reverse ordering of this comparator. default > Comparator thenComparing(Function keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key. default Comparator thenComparing(Function keyExtractor, Comparator keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator. default Comparator thenComparing(Comparator other) Returns a lexicographic-order comparator with another comparator. default Comparator thenComparingDouble(ToDoubleFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a double sort key. default Comparator thenComparingInt(ToIntFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts an int sort key. default Comparator thenComparingLong(ToLongFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a long sort key. Public methods compare Added in API level 1 public abstract int compare (T o1, T o2) Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared. o2 T: the second object to be compared. Returns int a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

Voltagecomparator

Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared. o2 T: the second object to be compared.

Returns a comparator that imposes the reverse of the natural ordering. The returned comparator is serializable and throws NullPointerException when comparing null.

Returns a comparator that compares Comparable objects in natural order. The returned comparator is serializable and throws NullPointerException when comparing null.

comparator用法

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)}. In other words, when the imposed ordering is consistent with equals, the equivalence classes defined by the equivalence relation of the equals method and the equivalence classes defined by the quotient of the compare method are the same. 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. See also: ComparableSerializable Summary Public methods abstract int compare(T o1, T o2) Compares its two arguments for order. static Comparator comparing(Function keyExtractor, Comparator keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator. static > Comparator comparing(Function keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingDouble(ToDoubleFunction keyExtractor) Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingInt(ToIntFunction keyExtractor) Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingLong(ToLongFunction keyExtractor) Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key. abstract boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. static > Comparator naturalOrder() Returns a comparator that compares Comparable objects in natural order. static Comparator nullsFirst(Comparator comparator) Returns a null-friendly comparator that considers null to be less than non-null. static Comparator nullsLast(Comparator comparator) Returns a null-friendly comparator that considers null to be greater than non-null. static > Comparator reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. default Comparator reversed() Returns a comparator that imposes the reverse ordering of this comparator. default > Comparator thenComparing(Function keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key. default Comparator thenComparing(Function keyExtractor, Comparator keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator. default Comparator thenComparing(Comparator other) Returns a lexicographic-order comparator with another comparator. default Comparator thenComparingDouble(ToDoubleFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a double sort key. default Comparator thenComparingInt(ToIntFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts an int sort key. default Comparator thenComparingLong(ToLongFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a long sort key. Public methods compare Added in API level 1 public abstract int compare (T o1, T o2) Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared. o2 T: the second object to be compared. Returns int a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. Throws NullPointerException if an argument is null and this comparator does not permit null arguments ClassCastException if the arguments' types prevent them from being compared by this comparator.

Flip flop

Digitalcomparator

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.

Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z.

The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z.

Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key.

Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key.

Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator.

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)}. In other words, when the imposed ordering is consistent with equals, the equivalence classes defined by the equivalence relation of the equals method and the equivalence classes defined by the quotient of the compare method are the same. 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. See also: ComparableSerializable Summary Public methods abstract int compare(T o1, T o2) Compares its two arguments for order. static Comparator comparing(Function keyExtractor, Comparator keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator. static > Comparator comparing(Function keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingDouble(ToDoubleFunction keyExtractor) Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingInt(ToIntFunction keyExtractor) Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingLong(ToLongFunction keyExtractor) Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key. abstract boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. static > Comparator naturalOrder() Returns a comparator that compares Comparable objects in natural order. static Comparator nullsFirst(Comparator comparator) Returns a null-friendly comparator that considers null to be less than non-null. static Comparator nullsLast(Comparator comparator) Returns a null-friendly comparator that considers null to be greater than non-null. static > Comparator reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. default Comparator reversed() Returns a comparator that imposes the reverse ordering of this comparator. default > Comparator thenComparing(Function keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key. default Comparator thenComparing(Function keyExtractor, Comparator keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator. default Comparator thenComparing(Comparator other) Returns a lexicographic-order comparator with another comparator. default Comparator thenComparingDouble(ToDoubleFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a double sort key. default Comparator thenComparingInt(ToIntFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts an int sort key. default Comparator thenComparingLong(ToLongFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a long sort key. Public methods compare Added in API level 1 public abstract int compare (T o1, T o2) Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared. o2 T: the second object to be compared. Returns int a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. Throws NullPointerException if an argument is null and this comparator does not permit null arguments ClassCastException if the arguments' types prevent them from being compared by this comparator.

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)}. In other words, when the imposed ordering is consistent with equals, the equivalence classes defined by the equivalence relation of the equals method and the equivalence classes defined by the quotient of the compare method are the same. 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. See also: ComparableSerializable Summary Public methods abstract int compare(T o1, T o2) Compares its two arguments for order. static Comparator comparing(Function keyExtractor, Comparator keyComparator) Accepts a function that extracts a sort key from a type T, and returns a Comparator that compares by that sort key using the specified Comparator. static > Comparator comparing(Function keyExtractor) Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingDouble(ToDoubleFunction keyExtractor) Accepts a function that extracts a double sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingInt(ToIntFunction keyExtractor) Accepts a function that extracts an int sort key from a type T, and returns a Comparator that compares by that sort key. static Comparator comparingLong(ToLongFunction keyExtractor) Accepts a function that extracts a long sort key from a type T, and returns a Comparator that compares by that sort key. abstract boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. static > Comparator naturalOrder() Returns a comparator that compares Comparable objects in natural order. static Comparator nullsFirst(Comparator comparator) Returns a null-friendly comparator that considers null to be less than non-null. static Comparator nullsLast(Comparator comparator) Returns a null-friendly comparator that considers null to be greater than non-null. static > Comparator reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. default Comparator reversed() Returns a comparator that imposes the reverse ordering of this comparator. default > Comparator thenComparing(Function keyExtractor) Returns a lexicographic-order comparator with a function that extracts a Comparable sort key. default Comparator thenComparing(Function keyExtractor, Comparator keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator. default Comparator thenComparing(Comparator other) Returns a lexicographic-order comparator with another comparator. default Comparator thenComparingDouble(ToDoubleFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a double sort key. default Comparator thenComparingInt(ToIntFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts an int sort key. default Comparator thenComparingLong(ToLongFunction keyExtractor) Returns a lexicographic-order comparator with a function that extracts a long sort key. Public methods compare Added in API level 1 public abstract int compare (T o1, T o2) Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.) The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0. Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z. API Note: It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1 T: the first object to be compared. o2 T: the second object to be compared. Returns int a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. Throws NullPointerException if an argument is null and this comparator does not permit null arguments ClassCastException if the arguments' types prevent them from being compared by this comparator.