Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) # Deque ``` interface Deque : Queue, SequencedCollection ``` |---| | [java.util.Deque](https://developer.android.com/reference/kotlin/java/util/Deque#) | |---| | Known Direct Subclasses [ArrayDeque](https://developer.android.com/reference/kotlin/java/util/ArrayDeque), [BlockingDeque](https://developer.android.com/reference/kotlin/java/util/concurrent/BlockingDeque), [ConcurrentLinkedDeque](https://developer.android.com/reference/kotlin/java/util/concurrent/ConcurrentLinkedDeque), [LinkedList](https://developer.android.com/reference/kotlin/java/util/LinkedList) |---|---| | [ArrayDeque](https://developer.android.com/reference/kotlin/java/util/ArrayDeque) | Resizable-array implementation of the `https://developer.android.com/reference/kotlin/java/util/Deque#` interface. | | [BlockingDeque](https://developer.android.com/reference/kotlin/java/util/concurrent/BlockingDeque) | A `https://developer.android.com/reference/kotlin/java/util/Deque#` that additionally supports blocking operations that wait for the deque to become non-empty when retrieving an element, and wait for space to become available in the deque when storing an element. | | [ConcurrentLinkedDeque](https://developer.android.com/reference/kotlin/java/util/concurrent/ConcurrentLinkedDeque) | An unbounded concurrent [deque](https://developer.android.com/reference/kotlin/java/util/Deque#) based on linked nodes. | | [LinkedList](https://developer.android.com/reference/kotlin/java/util/LinkedList) | Doubly-linked list implementation of the `List` and `Deque` interfaces. | | |---| | Known Indirect Subclasses [LinkedBlockingDeque](https://developer.android.com/reference/kotlin/java/util/concurrent/LinkedBlockingDeque) |---|---| | [LinkedBlockingDeque](https://developer.android.com/reference/kotlin/java/util/concurrent/LinkedBlockingDeque) | An optionally-bounded [blocking deque](https://developer.android.com/reference/kotlin/java/util/concurrent/BlockingDeque) based on linked nodes. | | A linear collection that supports element insertion and removal at both ends. The name *deque* is short for "double ended queue" and is usually pronounced "deck". Most `Deque` implementations place no fixed limits on the number of elements they may contain, but this interface supports capacity-restricted deques as well as those with no fixed size limit. This interface defines methods to access the elements at both ends of the deque. Methods are provided to insert, remove, and examine the element. Each of these methods exists in two forms: one throws an exception if the operation fails, the other returns a special value (either `null` or `false`, depending on the operation). The latter form of the insert operation is designed specifically for use with capacity-restricted `Deque` implementations; in most implementations, insert operations cannot fail. The twelve methods described above are summarized in the following table: |---|---|---|---|---| | | First Element (Head) || Last Element (Tail) || | | This interface extends the `https://developer.android.com/reference/kotlin/java/util/Queue` interface. When a deque is used as a queue, FIFO (First-In-First-Out) behavior results. Elements are added at the end of the deque and removed from the beginning. The methods inherited from the `Queue` interface are precisely equivalent to `Deque` methods as indicated in the following table: | `Queue` Method | Equivalent `Deque` Method | | `https://developer.android.com/reference/kotlin/java/util/Deque#add(java.util.Deque.E)` | `https://developer.android.com/reference/kotlin/java/util/Deque#addLast(java.util.Deque.E)` | | `https://developer.android.com/reference/kotlin/java/util/Deque#offer(java.util.Deque.E)` | `https://developer.android.com/reference/kotlin/java/util/Deque#offerLast(java.util.Deque.E)` | | `https://developer.android.com/reference/kotlin/java/util/Deque#remove()` | `https://developer.android.com/reference/kotlin/java/util/Deque#removeFirst()` | | `https://developer.android.com/reference/kotlin/java/util/Deque#poll()` | `https://developer.android.com/reference/kotlin/java/util/Deque#pollFirst()` | | `https://developer.android.com/reference/kotlin/java/util/Deque#element()` | `https://developer.android.com/reference/kotlin/java/util/Deque#getFirst()` | | `https://developer.android.com/reference/kotlin/java/util/Deque#peek()` | `https://developer.android.com/reference/kotlin/java/util/Deque#peekFirst()` | |---|---| Deques can also be used as LIFO (Last-In-First-Out) stacks. This interface should be used in preference to the legacy `https://developer.android.com/reference/kotlin/java/util/Stack` class. When a deque is used as a stack, elements are pushed and popped from the beginning of the deque. Stack methods are equivalent to `Deque` methods as indicated in the table below: | Stack Method | Equivalent `Deque` Method | | `https://developer.android.com/reference/kotlin/java/util/Deque#push(java.util.Deque.E)` | `https://developer.android.com/reference/kotlin/java/util/Deque#addFirst(java.util.Deque.E)` | | `https://developer.android.com/reference/kotlin/java/util/Deque#pop()` | `https://developer.android.com/reference/kotlin/java/util/Deque#removeFirst()` | | `https://developer.android.com/reference/kotlin/java/util/Deque#peek()` | `https://developer.android.com/reference/kotlin/java/util/Deque#peekFirst()` | |---|---| Note that the `https://developer.android.com/reference/kotlin/java/util/Deque#peek()` method works equally well when a deque is used as a queue or a stack; in either case, elements are drawn from the beginning of the deque. This interface provides two methods to remove interior elements, `https://developer.android.com/reference/kotlin/java/util/Deque#removeFirstOccurrence(kotlin.Any)` and `https://developer.android.com/reference/kotlin/java/util/Deque#removeLastOccurrence(kotlin.Any)`. Unlike the `https://developer.android.com/reference/kotlin/java/util/List` interface, this interface does not provide support for indexed access to elements. While `Deque` implementations are not strictly required to prohibit the insertion of null elements, they are strongly encouraged to do so. Users of any `Deque` implementations that do allow null elements are strongly encouraged *not* to take advantage of the ability to insert nulls. This is so because `null` is used as a special return value by various methods to indicate that the deque is empty. `Deque` implementations generally do not define element-based versions of the `equals` and `hashCode` methods, but instead inherit the identity-based versions from class `Object`. ## Summary | Public methods || |---|---| | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#add(java.util.Deque.E)(element: E)` Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and throwing an `IllegalStateException` if no space is currently available. | | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#addAll(kotlin.collections.Collection)(elements: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-collection/index.html)` Adds all of the elements in the specified collection at the end of this deque, as if by calling `https://developer.android.com/reference/kotlin/java/util/Deque#addLast(java.util.Deque.E)` on each one, in the order that they are returned by the collection's iterator. | | abstract [Unit](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#addFirst(java.util.Deque.E)(e: E)` Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. | | abstract [Unit](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#addLast(java.util.Deque.E)(e: E)` Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. | | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#contains(java.util.Deque.E)(element: E?)` Returns `true` if this deque contains the specified element. | | abstract [MutableIterator](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-mutable-iterator/index.html)\ | `https://developer.android.com/reference/kotlin/java/util/Deque#descendingIterator()()` Returns an iterator over the elements in this deque in reverse sequential order. | | abstract E | `https://developer.android.com/reference/kotlin/java/util/Deque#element()()` Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). | | abstract E | `https://developer.android.com/reference/kotlin/java/util/Deque#getFirst()()` Retrieves, but does not remove, the first element of this deque. | | abstract E | `https://developer.android.com/reference/kotlin/java/util/Deque#getLast()()` Retrieves, but does not remove, the last element of this deque. | | abstract [MutableIterator](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-mutable-iterator/index.html)\ | `https://developer.android.com/reference/kotlin/java/util/Deque#iterator()()` Returns an iterator over the elements in this deque in proper sequence. | | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#offer(java.util.Deque.E)(e: E)` Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and `false` if no space is currently available. | | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#offerFirst(java.util.Deque.E)(e: E)` Inserts the specified element at the front of this deque unless it would violate capacity restrictions. | | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#offerLast(java.util.Deque.E)(e: E)` Inserts the specified element at the end of this deque unless it would violate capacity restrictions. | | abstract E? | `https://developer.android.com/reference/kotlin/java/util/Deque#peek()()` Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns `null` if this deque is empty. | | abstract E? | `https://developer.android.com/reference/kotlin/java/util/Deque#peekFirst()()` Retrieves, but does not remove, the first element of this deque, or returns `null` if this deque is empty. | | abstract E? | `https://developer.android.com/reference/kotlin/java/util/Deque#peekLast()()` Retrieves, but does not remove, the last element of this deque, or returns `null` if this deque is empty. | | abstract E? | `https://developer.android.com/reference/kotlin/java/util/Deque#poll()()` Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns `null` if this deque is empty. | | abstract E? | `https://developer.android.com/reference/kotlin/java/util/Deque#pollFirst()()` Retrieves and removes the first element of this deque, or returns `null` if this deque is empty. | | abstract E? | `https://developer.android.com/reference/kotlin/java/util/Deque#pollLast()()` Retrieves and removes the last element of this deque, or returns `null` if this deque is empty. | | abstract E | `https://developer.android.com/reference/kotlin/java/util/Deque#pop()()` Pops an element from the stack represented by this deque. | | abstract [Unit](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#push(java.util.Deque.E)(e: E)` Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. | | abstract E | `https://developer.android.com/reference/kotlin/java/util/Deque#remove()()` Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). | | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#remove(java.util.Deque.E)(element: E?)` Removes the first occurrence of the specified element from this deque. | | abstract E | `https://developer.android.com/reference/kotlin/java/util/Deque#removeFirst()()` Retrieves and removes the first element of this deque. | | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#removeFirstOccurrence(kotlin.Any)(o: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-any/index.html?)` Removes the first occurrence of the specified element from this deque. | | abstract E | `https://developer.android.com/reference/kotlin/java/util/Deque#removeLast()()` Retrieves and removes the last element of this deque. | | abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#removeLastOccurrence(kotlin.Any)(o: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-any/index.html?)` Removes the last occurrence of the specified element from this deque. | | open [Deque](https://developer.android.com/reference/kotlin/java/util/Deque#)\ | `https://developer.android.com/reference/kotlin/java/util/Deque#reversed()()` Returns a reverse-ordered [view](https://developer.android.com/reference/kotlin/java/util/Collection#view) of this collection. | | Properties || |---|---| | abstract [Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html) | `https://developer.android.com/reference/kotlin/java/util/Deque#size:kotlin.Int` Returns the number of elements in this deque. | ## Public methods ### add Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun add(element: E): Boolean ``` Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and throwing an `IllegalStateException` if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use `https://developer.android.com/reference/kotlin/java/util/Deque#offer(java.util.Deque.E)`. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#addLast(java.util.Deque.E)`. | Parameters || |---|---| | `e` | the element to add | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` (as specified by `https://developer.android.com/reference/kotlin/java/util/Collection#add(java.util.Collection.E)`) | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element prevents it from being added to this deque | | `java.lang.IllegalArgumentException` | if some property of the specified element prevents it from being added to this deque | | `java.lang.IllegalStateException` | if the element cannot be added at this time due to capacity restrictions | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements | | `java.lang.UnsupportedOperationException` | if the `add` operation is not supported by this collection | ### addAll Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun addAll(elements: Collection): Boolean ``` Adds all of the elements in the specified collection at the end of this deque, as if by calling `https://developer.android.com/reference/kotlin/java/util/Deque#addLast(java.util.Deque.E)` on each one, in the order that they are returned by the collection's iterator. When using a capacity-restricted deque, it is generally preferable to call `https://developer.android.com/reference/kotlin/java/util/Deque#offer(java.util.Deque.E)` separately on each element. An exception encountered while trying to add an element may result in only some of the elements having been successfully added when the associated exception is thrown. | Parameters || |---|---| | `c` | the elements to be inserted into this deque | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` if this deque changed as a result of the call | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of an element of the specified collection prevents it from being added to this deque | | `java.lang.IllegalArgumentException` | if some property of an element of the specified collection prevents it from being added to this deque | | `java.lang.IllegalStateException` | if not all the elements can be added at this time due to insertion restrictions | | `java.lang.NullPointerException` | if the specified collection contains a null element and this deque does not permit null elements, or if the specified collection is null | | `java.lang.UnsupportedOperationException` | if the `addAll` operation is not supported by this collection | ### addFirst Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun addFirst(e: E): Unit ``` Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use method `https://developer.android.com/reference/kotlin/java/util/Deque#offerFirst(java.util.Deque.E)`. | Parameters || |---|---| | `e` | E: the element to add | | Exceptions || |---|---| | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements | | `java.lang.UnsupportedOperationException` | if this collection implementation does not support this operation | | `java.lang.ClassCastException` | if the class of the specified element prevents it from being added to this deque | | `java.lang.IllegalArgumentException` | if some property of the specified element prevents it from being added to this deque | | `java.lang.IllegalStateException` | if the element cannot be added at this time due to capacity restrictions | ### addLast Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun addLast(e: E): Unit ``` Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use method `https://developer.android.com/reference/kotlin/java/util/Deque#offerLast(java.util.Deque.E)`. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#add(java.util.Deque.E)`. | Parameters || |---|---| | `e` | E: the element to add | | Exceptions || |---|---| | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements | | `java.lang.UnsupportedOperationException` | if this collection implementation does not support this operation | | `java.lang.ClassCastException` | if the class of the specified element prevents it from being added to this deque | | `java.lang.IllegalArgumentException` | if some property of the specified element prevents it from being added to this deque | | `java.lang.IllegalStateException` | if the element cannot be added at this time due to capacity restrictions | ### contains Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun contains(element: E?): Boolean ``` Returns `true` if this deque contains the specified element. More formally, returns `true` if and only if this deque contains at least one element `e` such that `Objects.equals(o, e)`. | Parameters || |---|---| | `o` | element whose presence in this deque is to be tested | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` if this deque contains the specified element | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element is incompatible with this deque (java.util.Collection#) | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements (java.util.Collection#) | ### descendingIterator Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun descendingIterator(): MutableIterator ``` Returns an iterator over the elements in this deque in reverse sequential order. The elements will be returned in order from last (tail) to first (head). | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-mutable-iterator/index.html` | an iterator over the elements in this deque in reverse sequence | ### element Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun element(): E ``` Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from `https://developer.android.com/reference/kotlin/java/util/Deque#peek()` only in that it throws an exception if this deque is empty. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#getFirst()`. | Return || |---|---| | `E` | the head of the queue represented by this deque | | Exceptions || |---|---| | `java.util.NoSuchElementException` | if this deque is empty | ### getFirst Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun getFirst(): E ``` Retrieves, but does not remove, the first element of this deque. This method differs from `https://developer.android.com/reference/kotlin/java/util/Deque#peekFirst()` only in that it throws an exception if this deque is empty. | Return || |---|---| | `E` | the head of this deque | | Exceptions || |---|---| | `java.util.NoSuchElementException` | if this deque is empty | ### getLast Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun getLast(): E ``` Retrieves, but does not remove, the last element of this deque. This method differs from `https://developer.android.com/reference/kotlin/java/util/Deque#peekLast()` only in that it throws an exception if this deque is empty. | Return || |---|---| | `E` | the tail of this deque | | Exceptions || |---|---| | `java.util.NoSuchElementException` | if this deque is empty | ### iterator Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun iterator(): MutableIterator ``` Returns an iterator over the elements in this deque in proper sequence. The elements will be returned in order from first (head) to last (tail). | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-mutable-iterator/index.html` | an iterator over the elements in this deque in proper sequence | ### offer Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun offer(e: E): Boolean ``` Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and `false` if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to the `https://developer.android.com/reference/kotlin/java/util/Deque#add(java.util.Deque.E)` method, which can fail to insert an element only by throwing an exception. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#offerLast(java.util.Deque.E)`. | Parameters || |---|---| | `e` | E: the element to add | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` if the element was added to this deque, else `false` | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element prevents it from being added to this deque | | `java.lang.IllegalArgumentException` | if some property of the specified element prevents it from being added to this deque | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements | ### offerFirst Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun offerFirst(e: E): Boolean ``` Inserts the specified element at the front of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, this method is generally preferable to the `https://developer.android.com/reference/kotlin/java/util/Deque#addFirst(java.util.Deque.E)` method, which can fail to insert an element only by throwing an exception. | Parameters || |---|---| | `e` | E: the element to add | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` if the element was added to this deque, else `false` | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element prevents it from being added to this deque | | `java.lang.IllegalArgumentException` | if some property of the specified element prevents it from being added to this deque | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements | ### offerLast Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun offerLast(e: E): Boolean ``` Inserts the specified element at the end of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, this method is generally preferable to the `https://developer.android.com/reference/kotlin/java/util/Deque#addLast(java.util.Deque.E)` method, which can fail to insert an element only by throwing an exception. | Parameters || |---|---| | `e` | E: the element to add | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` if the element was added to this deque, else `false` | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element prevents it from being added to this deque | | `java.lang.IllegalArgumentException` | if some property of the specified element prevents it from being added to this deque | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements | ### peek Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun peek(): E? ``` Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns `null` if this deque is empty. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#peekFirst()`. | Return || |---|---| | `E?` | the head of the queue represented by this deque, or `null` if this deque is empty | ### peekFirst Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun peekFirst(): E? ``` Retrieves, but does not remove, the first element of this deque, or returns `null` if this deque is empty. | Return || |---|---| | `E?` | the head of this deque, or `null` if this deque is empty | ### peekLast Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun peekLast(): E? ``` Retrieves, but does not remove, the last element of this deque, or returns `null` if this deque is empty. | Return || |---|---| | `E?` | the tail of this deque, or `null` if this deque is empty | ### poll Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun poll(): E? ``` Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns `null` if this deque is empty. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#pollFirst()`. | Return || |---|---| | `E?` | the first element of this deque, or `null` if this deque is empty | ### pollFirst Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun pollFirst(): E? ``` Retrieves and removes the first element of this deque, or returns `null` if this deque is empty. | Return || |---|---| | `E?` | the head of this deque, or `null` if this deque is empty | ### pollLast Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun pollLast(): E? ``` Retrieves and removes the last element of this deque, or returns `null` if this deque is empty. | Return || |---|---| | `E?` | the tail of this deque, or `null` if this deque is empty | ### pop Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun pop(): E ``` Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#removeFirst()`. | Return || |---|---| | `E` | the element at the front of this deque (which is the top of the stack represented by this deque) | | Exceptions || |---|---| | `java.util.NoSuchElementException` | if this deque is empty | ### push Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun push(e: E): Unit ``` Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an `IllegalStateException` if no space is currently available. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#addFirst(java.util.Deque.E)`. | Parameters || |---|---| | `e` | E: the element to push | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element prevents it from being added to this deque | | `java.lang.IllegalArgumentException` | if some property of the specified element prevents it from being added to this deque | | `java.lang.IllegalStateException` | if the element cannot be added at this time due to capacity restrictions | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements | ### remove Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun remove(): E ``` Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from `https://developer.android.com/reference/kotlin/java/util/Deque#poll()` only in that it throws an exception if this deque is empty. This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#removeFirst()`. | Return || |---|---| | `E` | the head of the queue represented by this deque | | Exceptions || |---|---| | `java.util.NoSuchElementException` | if this deque is empty | ### remove Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun remove(element: E?): Boolean ``` Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element `e` such that `Objects.equals(o, e)` (if such an element exists). Returns `true` if this deque contained the specified element (or equivalently, if this deque changed as a result of the call). This method is equivalent to `https://developer.android.com/reference/kotlin/java/util/Deque#removeFirstOccurrence(kotlin.Any)`. | Parameters || |---|---| | `o` | element to be removed from this deque, if present | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` if an element was removed as a result of this call | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element is incompatible with this deque (java.util.Collection#) | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements (java.util.Collection#) | | `java.lang.UnsupportedOperationException` | if the `remove` operation is not supported by this collection | ### removeFirst Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun removeFirst(): E ``` Retrieves and removes the first element of this deque. This method differs from `https://developer.android.com/reference/kotlin/java/util/Deque#pollFirst()` only in that it throws an exception if this deque is empty. | Return || |---|---| | `E` | the head of this deque | | Exceptions || |---|---| | `java.lang.UnsupportedOperationException` | if this collection implementation does not support this operation | | `java.util.NoSuchElementException` | if this deque is empty | ### removeFirstOccurrence Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun removeFirstOccurrence(o: Any?): Boolean ``` Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element `e` such that `Objects.equals(o, e)` (if such an element exists). Returns `true` if this deque contained the specified element (or equivalently, if this deque changed as a result of the call). | Parameters || |---|---| | `o` | [Any](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-any/index.html)?: element to be removed from this deque, if present | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` if an element was removed as a result of this call | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element is incompatible with this deque (java.util.Collection#) | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements (java.util.Collection#) | ### removeLast Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun removeLast(): E ``` Retrieves and removes the last element of this deque. This method differs from `https://developer.android.com/reference/kotlin/java/util/Deque#pollLast()` only in that it throws an exception if this deque is empty. | Return || |---|---| | `E` | the tail of this deque | | Exceptions || |---|---| | `java.lang.UnsupportedOperationException` | if this collection implementation does not support this operation | | `java.util.NoSuchElementException` | if this deque is empty | ### removeLastOccurrence Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun removeLastOccurrence(o: Any?): Boolean ``` Removes the last occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the last element `e` such that `Objects.equals(o, e)` (if such an element exists). Returns `true` if this deque contained the specified element (or equivalently, if this deque changed as a result of the call). | Parameters || |---|---| | `o` | [Any](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-any/index.html)?: element to be removed from this deque, if present | | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html` | `true` if an element was removed as a result of this call | | Exceptions || |---|---| | `java.lang.ClassCastException` | if the class of the specified element is incompatible with this deque (java.util.Collection#) | | `java.lang.NullPointerException` | if the specified element is null and this deque does not permit null elements (java.util.Collection#) | ### reversed Added in [API level 35](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` open fun reversed(): Deque ``` Returns a reverse-ordered [view](https://developer.android.com/reference/kotlin/java/util/Collection#view) of this collection. The encounter order of elements in the returned view is the inverse of the encounter order of elements in this collection. The reverse ordering affects all order-sensitive operations, including those on the view collections of the returned view. If the collection implementation permits modifications to this view, the modifications "write through" to the underlying collection. Changes to the underlying collection might or might not be visible in this reversed view, depending upon the implementation. | Return || |---|---| | `https://developer.android.com/reference/kotlin/java/util/Deque#` | a reverse-ordered view of this collection, as a `Deque` | ## Properties ### size Added in [API level 9](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract val size: Int ``` Returns the number of elements in this deque. | Return || |---|---| | `https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html` | the number of elements in this deque |