Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) Summary: [Methods](https://developer.android.com/reference/java/util/Comparator#pubmethods)

# Comparator


`
public


interface
Comparator
`


`


`

|---|
| java.util.Comparator\<T\> |

Known indirect subclasses [ApplicationInfo.DisplayNameComparator](https://developer.android.com/reference/android/content/pm/ApplicationInfo.DisplayNameComparator), [Collator](https://developer.android.com/reference/java/text/Collator), [PackageItemInfo.DisplayNameComparator](https://developer.android.com/reference/android/content/pm/PackageItemInfo.DisplayNameComparator), [ResolveInfo.DisplayNameComparator](https://developer.android.com/reference/android/content/pm/ResolveInfo.DisplayNameComparator), [RuleBasedCollator](https://developer.android.com/reference/android/icu/text/RuleBasedCollator) [ApplicationInfo.DisplayNameComparator](https://developer.android.com/reference/android/content/pm/ApplicationInfo.DisplayNameComparator) [Collator](https://developer.android.com/reference/java/text/Collator) The `Collator` class performs locale-sensitive `String` comparison. [PackageItemInfo.DisplayNameComparator](https://developer.android.com/reference/android/content/pm/PackageItemInfo.DisplayNameComparator) [ResolveInfo.DisplayNameComparator](https://developer.android.com/reference/android/content/pm/ResolveInfo.DisplayNameComparator) [RuleBasedCollator](https://developer.android.com/reference/android/icu/text/RuleBasedCollator)
RuleBasedCollator is a concrete subclass of Collator.


<br />

*** ** * ** ***

A comparison function, which imposes a *total ordering* on
some collection of objects. Comparators can be passed to a sort
method (such as `https://developer.android.com/reference/java/util/Collections#sort(java.util.List<T>,%20java.util.Comparator<?%20super%20T>)` or `https://developer.android.com/reference/java/util/Arrays#sort(T[],%20java.util.Comparator<?%20super%20T>)`) 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](https://developer.android.com/reference/java/util/SortedSet) or
[sorted maps](https://developer.android.com/reference/java/util/SortedMap)), or to provide an ordering for
collections of objects that don't have a [natural ordering](https://developer.android.com/reference/java/lang/Comparable).


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
`https://developer.android.com/reference/java/util/Set#add(E)` 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 `https://developer.android.com/reference/java/util/TreeSet`, `https://developer.android.com/reference/java/util/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' `https://developer.android.com/reference/java/lang/Object#equals(java.lang.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](https://reference/java/util/package-summary.html#CollectionsFramework).
**See also:**

- `https://developer.android.com/reference/java/lang/Comparable`
- `https://developer.android.com/reference/java/io/Serializable`

## Summary

| ### Public methods ||
|---|---|
| ` abstract int` | ` https://developer.android.com/reference/java/util/Comparator#compare(T,%20T)(T o1, T o2) ` Compares its two arguments for order. |
| ` static <T, U> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#comparing(java.util.function.Function<?%20super%20T,?%20extends%20U>,%20java.util.Comparator<?%20super%20U>)(https://developer.android.com/reference/java/util/function/Function<? super T, ? extends U> keyExtractor, https://developer.android.com/reference/java/util/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 `https://developer.android.com/reference/java/util/Comparator`. |
| ` static <T, U extends https://developer.android.com/reference/java/lang/Comparable<? super U>> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#comparing(java.util.function.Function<?%20super%20T,?%20extends%20U>)(https://developer.android.com/reference/java/util/function/Function<? super T, ? extends U> keyExtractor) ` Accepts a function that extracts a `https://developer.android.com/reference/java/lang/Comparable` sort key from a type `T`, and returns a `Comparator<T>` that compares by that sort key. |
| ` static <T> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#comparingDouble(java.util.function.ToDoubleFunction<?%20super%20T>)(https://developer.android.com/reference/java/util/function/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. |
| ` static <T> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#comparingInt(java.util.function.ToIntFunction<?%20super%20T>)(https://developer.android.com/reference/java/util/function/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. |
| ` static <T> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#comparingLong(java.util.function.ToLongFunction<?%20super%20T>)(https://developer.android.com/reference/java/util/function/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. |
| ` abstract boolean` | ` https://developer.android.com/reference/java/util/Comparator#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object obj) ` Indicates whether some other object is "equal to" this comparator. |
| ` static <T extends https://developer.android.com/reference/java/lang/Comparable<? super T>> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#naturalOrder()() ` Returns a comparator that compares `https://developer.android.com/reference/java/lang/Comparable` objects in natural order. |
| ` static <T> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#nullsFirst(java.util.Comparator<?%20super%20T>)(https://developer.android.com/reference/java/util/Comparator<? super T> comparator) ` Returns a null-friendly comparator that considers `null` to be less than non-null. |
| ` static <T> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#nullsLast(java.util.Comparator<?%20super%20T>)(https://developer.android.com/reference/java/util/Comparator<? super T> comparator) ` Returns a null-friendly comparator that considers `null` to be greater than non-null. |
| ` static <T extends https://developer.android.com/reference/java/lang/Comparable<? super T>> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#reverseOrder()() ` Returns a comparator that imposes the reverse of the *natural ordering*. |
| ` default https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#reversed()() ` Returns a comparator that imposes the reverse ordering of this comparator. |
| ` default <U extends https://developer.android.com/reference/java/lang/Comparable<? super U>> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#thenComparing(java.util.function.Function<?%20super%20T,?%20extends%20U>)(https://developer.android.com/reference/java/util/function/Function<? super T, ? extends U> keyExtractor) ` Returns a lexicographic-order comparator with a function that extracts a `Comparable` sort key. |
| ` default <U> https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#thenComparing(java.util.function.Function<?%20super%20T,?%20extends%20U>,%20java.util.Comparator<?%20super%20U>)(https://developer.android.com/reference/java/util/function/Function<? super T, ? extends U> keyExtractor, https://developer.android.com/reference/java/util/Comparator<? super U> keyComparator) ` Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given `Comparator`. |
| ` default https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#thenComparing(java.util.Comparator<?%20super%20T>)(https://developer.android.com/reference/java/util/Comparator<? super T> other) ` Returns a lexicographic-order comparator with another comparator. |
| ` default https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#thenComparingDouble(java.util.function.ToDoubleFunction<?%20super%20T>)(https://developer.android.com/reference/java/util/function/ToDoubleFunction<? super T> keyExtractor) ` Returns a lexicographic-order comparator with a function that extracts a `double` sort key. |
| ` default https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#thenComparingInt(java.util.function.ToIntFunction<?%20super%20T>)(https://developer.android.com/reference/java/util/function/ToIntFunction<? super T> keyExtractor) ` Returns a lexicographic-order comparator with a function that extracts an `int` sort key. |
| ` default https://developer.android.com/reference/java/util/Comparator<T>` | ` https://developer.android.com/reference/java/util/Comparator#thenComparingLong(java.util.function.ToLongFunction<?%20super%20T>)(https://developer.android.com/reference/java/util/function/ToLongFunction<? super T> keyExtractor) ` Returns a lexicographic-order comparator with a function that extracts a `long` sort key. |

## Public methods

### compare

Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
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 `https://developer.android.com/reference/java/lang/Integer#signum(int)``(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`.

<br />

##### 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. <br /> |
| `o2` | `T`: the second object to be compared. <br /> |

| Returns ||
|---|---|
| `int` | a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` | if the arguments' types prevent them from being compared by this comparator. |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if an argument is null and this comparator does not permit null arguments |

### comparing

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static 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 `https://developer.android.com/reference/java/util/Comparator`.

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

<br />

##### API Note:

- For example, to obtain a `Comparator` that compares `Person` objects by their last name ignoring case differences,

      Comparator<Person> cmp = Comparator.comparing(
                  Person::getLastName,
                  String.CASE_INSENSITIVE_ORDER);

| Parameters ||
|---|---|
| `keyExtractor` | `Function`: the function used to extract the sort key <br /> |
| `keyComparator` | `Comparator`: the `Comparator` used to compare the sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that compares by an extracted key using the specified `Comparator` <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if either argument is null |

### comparing

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static Comparator<T> comparing (Function<? super T, ? extends U> keyExtractor)
```

Accepts a function that extracts a `https://developer.android.com/reference/java/lang/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.

<br />

##### API Note:

- For example, to obtain a `Comparator` that compares `Person` objects by their last name,

      Comparator<Person> byLastName = Comparator.comparing(Person::getLastName);

| Parameters ||
|---|---|
| `keyExtractor` | `Function`: the function used to extract the `https://developer.android.com/reference/java/lang/Comparable` sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that compares by an extracted key <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null |

### comparingDouble

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static Comparator<T> comparingDouble (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.

<br />

| Parameters ||
|---|---|
| `keyExtractor` | `ToDoubleFunction`: the function used to extract the double sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that compares by an extracted key <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null |

**See also:**

- `https://developer.android.com/reference/java/util/Comparator#comparing(java.util.function.Function<?%20super%20T,?%20extends%20U>)`

### comparingInt

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static Comparator<T> comparingInt (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.

<br />

| Parameters ||
|---|---|
| `keyExtractor` | `ToIntFunction`: the function used to extract the integer sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that compares by an extracted key <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null |

**See also:**

- `https://developer.android.com/reference/java/util/Comparator#comparing(java.util.function.Function<?%20super%20T,?%20extends%20U>)`

### comparingLong

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static Comparator<T> comparingLong (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.

<br />

| Parameters ||
|---|---|
| `keyExtractor` | `ToLongFunction`: the function used to extract the long sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that compares by an extracted key <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null |

**See also:**

- `https://developer.android.com/reference/java/util/Comparator#comparing(java.util.function.Function<?%20super%20T,?%20extends%20U>)`

### equals

Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public abstract boolean equals (Object obj)
```

Indicates whether some other object is "equal to"
this comparator. This method must obey the general contract of
`https://developer.android.com/reference/java/lang/Object#equals(java.lang.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
`https://developer.android.com/reference/java/lang/Integer#signum(int)``(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.

<br />

| Parameters ||
|---|---|
| `obj` | `Object`: the reference object with which to compare. <br /> |

| Returns ||
|---|---|
| `boolean` | `true` only if the specified object is also a comparator and it imposes the same ordering as this comparator. <br /> |

**See also:**

- `https://developer.android.com/reference/java/lang/Object#equals(java.lang.Object)`
- `https://developer.android.com/reference/java/lang/Object#hashCode()`

### naturalOrder

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static Comparator<T> naturalOrder ()
```

Returns a comparator that compares `https://developer.android.com/reference/java/lang/Comparable` objects in natural
order.

The returned comparator is serializable and throws `https://developer.android.com/reference/java/lang/NullPointerException` when comparing `null`.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that imposes the *natural ordering* on `Comparable` objects. <br /> |

**See also:**

- `https://developer.android.com/reference/java/lang/Comparable`

### nullsFirst

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static 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. 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.

<br />

| Parameters ||
|---|---|
| `comparator` | `Comparator`: a `Comparator` for comparing non-null values <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that considers `null` to be less than non-null, and compares non-null objects with the supplied `Comparator`. <br /> |

### nullsLast

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static 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. 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.

<br />

| Parameters ||
|---|---|
| `comparator` | `Comparator`: a `Comparator` for comparing non-null values <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that considers `null` to be greater than non-null, and compares non-null objects with the supplied `Comparator`. <br /> |

### reverseOrder

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public static Comparator<T> reverseOrder ()
```

Returns a comparator that imposes the reverse of the *natural
ordering*.

The returned comparator is serializable and throws `https://developer.android.com/reference/java/lang/NullPointerException` when comparing `null`.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that imposes the reverse of the *natural ordering* on `Comparable` objects. <br /> |

**See also:**

- `https://developer.android.com/reference/java/lang/Comparable`

### reversed

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Comparator<T> reversed ()
```

Returns a comparator that imposes the reverse ordering of this
comparator.

<br />

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a comparator that imposes the reverse ordering of this comparator. <br /> |

### thenComparing

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Comparator<T> thenComparing (Function<? super T, ? extends U> keyExtractor)
```

Returns a lexicographic-order comparator with a function that
extracts a `Comparable` sort key.

<br />

##### Implementation Requirements:

- This default implementation behaves as if `thenComparing(comparing(keyExtractor))`.

| Parameters ||
|---|---|
| `keyExtractor` | `Function`: the function used to extract the `https://developer.android.com/reference/java/lang/Comparable` sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a lexicographic-order comparator composed of this and then the `https://developer.android.com/reference/java/lang/Comparable` sort key. <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null. |

**See also:**

- `https://developer.android.com/reference/java/util/Comparator#comparing(java.util.function.Function<?%20super%20T,?%20extends%20U>)`
- `https://developer.android.com/reference/java/util/Comparator#thenComparing(java.util.Comparator<?%20super%20T>)`

### thenComparing

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Comparator<T> thenComparing (Function<? super T, ? extends U> keyExtractor, 
                Comparator<? super U> keyComparator)
```

Returns a lexicographic-order comparator with a function that
extracts a key to be compared with the given `Comparator`.

<br />

##### Implementation Requirements:

- This default implementation behaves as if `thenComparing(comparing(keyExtractor, cmp))`.

| Parameters ||
|---|---|
| `keyExtractor` | `Function`: the function used to extract the sort key <br /> |
| `keyComparator` | `Comparator`: the `Comparator` used to compare the sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a lexicographic-order comparator composed of this comparator and then comparing on the key extracted by the keyExtractor function <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if either argument is null. |

**See also:**

- `https://developer.android.com/reference/java/util/Comparator#comparing(java.util.function.Function<?%20super%20T,?%20extends%20U>,%20java.util.Comparator<?%20super%20U>)`
- `https://developer.android.com/reference/java/util/Comparator#thenComparing(java.util.Comparator<?%20super%20T>)`

### thenComparing

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Comparator<T> thenComparing (Comparator<? super T> other)
```

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.

<br />

##### API Note:

- For example, to sort a collection of `String` based on the length and then case-insensitive natural ordering, the comparator can be composed using following code,

      Comparator<String> cmp = Comparator.comparingInt(String::length)
                  .thenComparing(String.CASE_INSENSITIVE_ORDER);

| Parameters ||
|---|---|
| `other` | `Comparator`: the other comparator to be used when this comparator compares two objects that are equal. <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a lexicographic-order comparator composed of this and then the other comparator <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null. |

### thenComparingDouble

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Comparator<T> thenComparingDouble (ToDoubleFunction<? super T> keyExtractor)
```

Returns a lexicographic-order comparator with a function that
extracts a `double` sort key.

<br />

##### Implementation Requirements:

- This default implementation behaves as if `thenComparing(comparingDouble(keyExtractor))`.

| Parameters ||
|---|---|
| `keyExtractor` | `ToDoubleFunction`: the function used to extract the double sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a lexicographic-order comparator composed of this and then the `double` sort key <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null. |

**See also:**

- `https://developer.android.com/reference/java/util/Comparator#comparingDouble(java.util.function.ToDoubleFunction<?%20super%20T>)`
- `https://developer.android.com/reference/java/util/Comparator#thenComparing(java.util.Comparator<?%20super%20T>)`

### thenComparingInt

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Comparator<T> thenComparingInt (ToIntFunction<? super T> keyExtractor)
```

Returns a lexicographic-order comparator with a function that
extracts an `int` sort key.

<br />

##### Implementation Requirements:

- This default implementation behaves as if `thenComparing(comparingInt(keyExtractor))`.

| Parameters ||
|---|---|
| `keyExtractor` | `ToIntFunction`: the function used to extract the integer sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a lexicographic-order comparator composed of this and then the `int` sort key <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null. |

**See also:**

- `https://developer.android.com/reference/java/util/Comparator#comparingInt(java.util.function.ToIntFunction<?%20super%20T>)`
- `https://developer.android.com/reference/java/util/Comparator#thenComparing(java.util.Comparator<?%20super%20T>)`

### thenComparingLong

Added in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public Comparator<T> thenComparingLong (ToLongFunction<? super T> keyExtractor)
```

Returns a lexicographic-order comparator with a function that
extracts a `long` sort key.

<br />

##### Implementation Requirements:

- This default implementation behaves as if `thenComparing(comparingLong(keyExtractor))`.

| Parameters ||
|---|---|
| `keyExtractor` | `ToLongFunction`: the function used to extract the long sort key <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/java/util/Comparator<T>` | a lexicographic-order comparator composed of this and then the `long` sort key <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the argument is null. |

**See also:**

- `https://developer.android.com/reference/java/util/Comparator#comparingLong(java.util.function.ToLongFunction<?%20super%20T>)`
- `https://developer.android.com/reference/java/util/Comparator#thenComparing(java.util.Comparator<?%20super%20T>)`