Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) Summary: [Protected Ctors](https://developer.android.com/reference/java/util/AbstractQueue#proctors) \| [Methods](https://developer.android.com/reference/java/util/AbstractQueue#pubmethods) \| [Inherited Methods](https://developer.android.com/reference/java/util/AbstractQueue#inhmethods)

# AbstractQueue

` public abstract class AbstractQueue `   
` ` ` extends https://developer.android.com/reference/java/util/AbstractCollection<E> ` ` implements https://developer.android.com/reference/java/util/Queue<E> `

|---|---|---|
| [java.lang.Object](https://developer.android.com/reference/java/lang/Object) |||
| ↳ | [java.util.AbstractCollection](https://developer.android.com/reference/java/util/AbstractCollection)\<E\> ||
|   | ↳ | java.util.AbstractQueue\<E\> |

Known direct subclasses [ArrayBlockingQueue](https://developer.android.com/reference/java/util/concurrent/ArrayBlockingQueue)\<E\>, [ConcurrentLinkedQueue](https://developer.android.com/reference/java/util/concurrent/ConcurrentLinkedQueue)\<E\>, [DelayQueue](https://developer.android.com/reference/java/util/concurrent/DelayQueue)\<E extends [Delayed](https://developer.android.com/reference/java/util/concurrent/Delayed)\>, [LinkedBlockingDeque](https://developer.android.com/reference/java/util/concurrent/LinkedBlockingDeque)\<E\>, [LinkedBlockingQueue](https://developer.android.com/reference/java/util/concurrent/LinkedBlockingQueue)\<E\>, [LinkedTransferQueue](https://developer.android.com/reference/java/util/concurrent/LinkedTransferQueue)\<E\>, [PriorityBlockingQueue](https://developer.android.com/reference/java/util/concurrent/PriorityBlockingQueue)\<E\>, [PriorityQueue](https://developer.android.com/reference/java/util/PriorityQueue)\<E\>, [SynchronousQueue](https://developer.android.com/reference/java/util/concurrent/SynchronousQueue)\<E\> [ArrayBlockingQueue](https://developer.android.com/reference/java/util/concurrent/ArrayBlockingQueue)\<E\> A bounded [blocking queue](https://developer.android.com/reference/java/util/concurrent/BlockingQueue) backed by an array. [ConcurrentLinkedQueue](https://developer.android.com/reference/java/util/concurrent/ConcurrentLinkedQueue)\<E\> An unbounded thread-safe [queue](https://developer.android.com/reference/java/util/Queue) based on linked nodes. [DelayQueue](https://developer.android.com/reference/java/util/concurrent/DelayQueue)\<E extends [Delayed](https://developer.android.com/reference/java/util/concurrent/Delayed)\> An unbounded [blocking queue](https://developer.android.com/reference/java/util/concurrent/BlockingQueue) of `https://developer.android.com/reference/java/util/concurrent/Delayed` elements, in which an element generally becomes eligible for removal when its delay has expired. [LinkedBlockingDeque](https://developer.android.com/reference/java/util/concurrent/LinkedBlockingDeque)\<E\> An optionally-bounded [blocking deque](https://developer.android.com/reference/java/util/concurrent/BlockingDeque) based on linked nodes. [LinkedBlockingQueue](https://developer.android.com/reference/java/util/concurrent/LinkedBlockingQueue)\<E\> An optionally-bounded [blocking queue](https://developer.android.com/reference/java/util/concurrent/BlockingQueue) based on linked nodes. [LinkedTransferQueue](https://developer.android.com/reference/java/util/concurrent/LinkedTransferQueue)\<E\> An unbounded `https://developer.android.com/reference/java/util/concurrent/TransferQueue` based on linked nodes. [PriorityBlockingQueue](https://developer.android.com/reference/java/util/concurrent/PriorityBlockingQueue)\<E\> An unbounded [blocking queue](https://developer.android.com/reference/java/util/concurrent/BlockingQueue) that uses the same ordering rules as class `https://developer.android.com/reference/java/util/PriorityQueue` and supplies blocking retrieval operations. [PriorityQueue](https://developer.android.com/reference/java/util/PriorityQueue)\<E\> An unbounded priority [queue](https://developer.android.com/reference/java/util/Queue) based on a priority heap. [SynchronousQueue](https://developer.android.com/reference/java/util/concurrent/SynchronousQueue)\<E\> A [blocking queue](https://developer.android.com/reference/java/util/concurrent/BlockingQueue) in which each insert operation must wait for a corresponding remove operation by another thread, and vice versa.   

*** ** * ** ***

This class provides skeletal implementations of some `https://developer.android.com/reference/java/util/Queue` operations. The implementations in this class are appropriate when the base implementation does *not* allow `null` elements. Methods `https://developer.android.com/reference/java/util/AbstractQueue#add(E)`, `https://developer.android.com/reference/java/util/AbstractQueue#remove()`, and `https://developer.android.com/reference/java/util/AbstractQueue#element()` are based on `https://developer.android.com/reference/java/util/Queue#offer(E)`, `https://developer.android.com/reference/java/util/Queue#poll()`, and `https://developer.android.com/reference/java/util/Queue#peek()`, respectively, but throw exceptions instead of indicating failure via `false` or `null` returns.

A `Queue` implementation that extends this class must minimally define a method `https://developer.android.com/reference/java/util/Queue#offer(E)` which does not permit insertion of `null` elements, along with methods `https://developer.android.com/reference/java/util/Queue#peek()`, `https://developer.android.com/reference/java/util/Queue#poll()`, `https://developer.android.com/reference/java/util/Collection#size()`, and `https://developer.android.com/reference/java/util/Collection#iterator()`. Typically, additional methods will be overridden as well. If these requirements cannot be met, consider instead subclassing `https://developer.android.com/reference/java/util/AbstractCollection`.

## Summary

| ### Protected constructors ||
|---|---|
| ` https://developer.android.com/reference/java/util/AbstractQueue#AbstractQueue()() ` Constructor for use by subclasses. |

| ### Public methods ||
|---|---|
| ` boolean` | ` https://developer.android.com/reference/java/util/AbstractQueue#add(E)(E e) ` Inserts the specified element into this queue 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. |
| ` boolean` | ` https://developer.android.com/reference/java/util/AbstractQueue#addAll(java.util.Collection<?%20extends%20E>)(https://developer.android.com/reference/java/util/Collection<? extends E> c) ` Adds all of the elements in the specified collection to this queue. |
| ` void` | ` https://developer.android.com/reference/java/util/AbstractQueue#clear()() ` Removes all of the elements from this queue. |
| ` E` | ` https://developer.android.com/reference/java/util/AbstractQueue#element()() ` Retrieves, but does not remove, the head of this queue. |
| ` E` | ` https://developer.android.com/reference/java/util/AbstractQueue#remove()() ` Retrieves and removes the head of this queue. |

### Inherited methods

From class ` https://developer.android.com/reference/java/util/AbstractCollection ` ` boolean` ` https://developer.android.com/reference/java/util/AbstractCollection#add(E)(E e) `

Ensures that this collection contains the specified element (optional operation).
` boolean` ` https://developer.android.com/reference/java/util/AbstractCollection#addAll(java.util.Collection<?%20extends%20E>)(https://developer.android.com/reference/java/util/Collection<? extends E> c) `

Adds all of the elements in the specified collection to this collection (optional operation).
` void` ` https://developer.android.com/reference/java/util/AbstractCollection#clear()() `

Removes all of the elements from this collection (optional operation).
` boolean` ` https://developer.android.com/reference/java/util/AbstractCollection#contains(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) `

Returns `true` if this collection contains the specified element.
` boolean` ` https://developer.android.com/reference/java/util/AbstractCollection#containsAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) `

Returns `true` if this collection contains all of the elements in the specified collection.
` boolean` ` https://developer.android.com/reference/java/util/AbstractCollection#isEmpty()() `

Returns `true` if this collection contains no elements.
` abstract https://developer.android.com/reference/java/util/Iterator<E>` ` https://developer.android.com/reference/java/util/AbstractCollection#iterator()() `

Returns an iterator over the elements contained in this collection.
` boolean` ` https://developer.android.com/reference/java/util/AbstractCollection#remove(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) `

Removes a single instance of the specified element from this collection, if it is present (optional operation).
` boolean` ` https://developer.android.com/reference/java/util/AbstractCollection#removeAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) `

Removes all of this collection's elements that are also contained in the specified collection (optional operation).
` boolean` ` https://developer.android.com/reference/java/util/AbstractCollection#retainAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) `

Retains only the elements in this collection that are contained in the specified collection (optional operation).
` abstract int` ` https://developer.android.com/reference/java/util/AbstractCollection#size()() `

Returns the number of elements in this collection.
` <T> T[]` ` https://developer.android.com/reference/java/util/AbstractCollection#toArray(T[])(T[] a) `

Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
` https://developer.android.com/reference/java/lang/Object` ` https://developer.android.com/reference/java/util/AbstractCollection#toArray()() `

Returns an array containing all of the elements in this collection.
` https://developer.android.com/reference/java/lang/String` ` https://developer.android.com/reference/java/util/AbstractCollection#toString()() `

Returns a string representation of this collection.
From class ` https://developer.android.com/reference/java/lang/Object ` ` https://developer.android.com/reference/java/lang/Object` ` https://developer.android.com/reference/java/lang/Object#clone()() `

Creates and returns a copy of this object.
` boolean` ` https://developer.android.com/reference/java/lang/Object#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object obj) `

Indicates whether some other object is "equal to" this one.
` void` ` https://developer.android.com/reference/java/lang/Object#finalize()() `

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
` final https://developer.android.com/reference/java/lang/Class<?>` ` https://developer.android.com/reference/java/lang/Object#getClass()() `

Returns the runtime class of this `Object`.
` int` ` https://developer.android.com/reference/java/lang/Object#hashCode()() `

Returns a hash code value for the object.
` final void` ` https://developer.android.com/reference/java/lang/Object#notify()() `

Wakes up a single thread that is waiting on this object's monitor.
` final void` ` https://developer.android.com/reference/java/lang/Object#notifyAll()() `

Wakes up all threads that are waiting on this object's monitor.
` https://developer.android.com/reference/java/lang/String` ` https://developer.android.com/reference/java/lang/Object#toString()() `

Returns a string representation of the object.
` final void` ` https://developer.android.com/reference/java/lang/Object#wait(long,%20int)(long timeoutMillis, int nanos) `

Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed.
` final void` ` https://developer.android.com/reference/java/lang/Object#wait(long)(long timeoutMillis) `

Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed.
` final void` ` https://developer.android.com/reference/java/lang/Object#wait()() `

Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*.
From interface ` https://developer.android.com/reference/java/util/Collection ` ` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#add(E)(E e) `

Ensures that this collection contains the specified element (optional operation).
` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#addAll(java.util.Collection<?%20extends%20E>)(https://developer.android.com/reference/java/util/Collection<? extends E> c) `

Adds all of the elements in the specified collection to this collection (optional operation).
` abstract void` ` https://developer.android.com/reference/java/util/Collection#clear()() `

Removes all of the elements from this collection (optional operation).
` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#contains(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) `

Returns `true` if this collection contains the specified element.
` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#containsAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) `

Returns `true` if this collection contains all of the elements in the specified collection.
` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) `

Compares the specified object with this collection for equality.
` abstract int` ` https://developer.android.com/reference/java/util/Collection#hashCode()() `

Returns the hash code value for this collection.
` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#isEmpty()() `

Returns `true` if this collection contains no elements.
` abstract https://developer.android.com/reference/java/util/Iterator<E>` ` https://developer.android.com/reference/java/util/Collection#iterator()() `

Returns an iterator over the elements in this collection.
` default https://developer.android.com/reference/java/util/stream/Stream<E>` ` https://developer.android.com/reference/java/util/Collection#parallelStream()() `

Returns a possibly parallel `Stream` with this collection as its source.
` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#remove(java.lang.Object)(https://developer.android.com/reference/java/lang/Object o) `

Removes a single instance of the specified element from this collection, if it is present (optional operation).
` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#removeAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) `

Removes all of this collection's elements that are also contained in the specified collection (optional operation).
` default boolean` ` https://developer.android.com/reference/java/util/Collection#removeIf(java.util.function.Predicate<?%20super%20E>)(https://developer.android.com/reference/java/util/function/Predicate<? super E> filter) `

Removes all of the elements of this collection that satisfy the given predicate (optional operation).
` abstract boolean` ` https://developer.android.com/reference/java/util/Collection#retainAll(java.util.Collection<?>)(https://developer.android.com/reference/java/util/Collection<?> c) `

Retains only the elements in this collection that are contained in the specified collection (optional operation).
` abstract int` ` https://developer.android.com/reference/java/util/Collection#size()() `

Returns the number of elements in this collection.
` default https://developer.android.com/reference/java/util/Spliterator<E>` ` https://developer.android.com/reference/java/util/Collection#spliterator()() `

Creates a `https://developer.android.com/reference/java/util/Spliterator` over the elements in this collection.
` default https://developer.android.com/reference/java/util/stream/Stream<E>` ` https://developer.android.com/reference/java/util/Collection#stream()() `

Returns a sequential `Stream` with this collection as its source.
` abstract <T> T[]` ` https://developer.android.com/reference/java/util/Collection#toArray(T[])(T[] a) `

Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
` abstract https://developer.android.com/reference/java/lang/Object` ` https://developer.android.com/reference/java/util/Collection#toArray()() `

Returns an array containing all of the elements in this collection.
` default <T> T[]` ` https://developer.android.com/reference/java/util/Collection#toArray(java.util.function.IntFunction<T[]>)(https://developer.android.com/reference/java/util/function/IntFunction<T[]> generator) `

Returns an array containing all of the elements in this collection, using the provided `generator` function to allocate the returned array.
From interface ` https://developer.android.com/reference/java/util/Queue ` ` abstract boolean` ` https://developer.android.com/reference/java/util/Queue#add(E)(E e) `

Inserts the specified element into this queue 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 E` ` https://developer.android.com/reference/java/util/Queue#element()() `

Retrieves, but does not remove, the head of this queue.
` abstract boolean` ` https://developer.android.com/reference/java/util/Queue#offer(E)(E e) `

Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.
` abstract E` ` https://developer.android.com/reference/java/util/Queue#peek()() `

Retrieves, but does not remove, the head of this queue, or returns `null` if this queue is empty.
` abstract E` ` https://developer.android.com/reference/java/util/Queue#poll()() `

Retrieves and removes the head of this queue, or returns `null` if this queue is empty.
` abstract E` ` https://developer.android.com/reference/java/util/Queue#remove()() `

Retrieves and removes the head of this queue.
From interface ` https://developer.android.com/reference/java/lang/Iterable ` ` default void` ` https://developer.android.com/reference/java/lang/Iterable#forEach(java.util.function.Consumer<?%20super%20T>)(https://developer.android.com/reference/java/util/function/Consumer<? super T> action) `

Performs the given action for each element of the `Iterable` until all elements have been processed or the action throws an exception.
` abstract https://developer.android.com/reference/java/util/Iterator<E>` ` https://developer.android.com/reference/java/lang/Iterable#iterator()() `

Returns an iterator over elements of type `T`.
` default https://developer.android.com/reference/java/util/Spliterator<E>` ` https://developer.android.com/reference/java/lang/Iterable#spliterator()() `

Creates a `https://developer.android.com/reference/java/util/Spliterator` over the elements described by this `Iterable`.

## Protected constructors

### AbstractQueue

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

```
protected AbstractQueue ()
```

Constructor for use by subclasses.

<br />

## Public methods

### add

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

```
public boolean add (E e)
```

Inserts the specified element into this queue 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.

This implementation returns `true` if `offer` succeeds, else throws an `IllegalStateException`.

<br />

| Parameters ||
|---|---|
| `e` | `E`: the element to add <br /> |

| Returns ||
|---|---|
| `boolean` | `true` (as specified by `https://developer.android.com/reference/java/util/Collection#add(E)`) <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` | if the class of the specified element prevents it from being added to this queue |
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` | if some property of this element prevents it from being added to this queue |
| `https://developer.android.com/reference/java/lang/IllegalStateException` | if the element cannot be added at this time due to capacity restrictions |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified element is null and this queue does not permit null elements |

### addAll

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

```
public boolean addAll (Collection<? extends E> c)
```

Adds all of the elements in the specified collection to this queue. Attempts to addAll of a queue to itself result in `IllegalArgumentException`. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

This implementation iterates over the specified collection, and adds each element returned by the iterator to this queue, in turn. A runtime exception encountered while trying to add an element (including, in particular, a `null` element) may result in only some of the elements having been successfully added when the associated exception is thrown.

<br />

| Parameters ||
|---|---|
| `c` | `Collection`: collection containing elements to be added to this queue <br /> |

| Returns ||
|---|---|
| `boolean` | `true` if this queue changed as a result of the call <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/ClassCastException` | if the class of an element of the specified collection prevents it from being added to this queue |
| `https://developer.android.com/reference/java/lang/IllegalArgumentException` | if some property of an element of the specified collection prevents it from being added to this queue, or if the specified collection is this queue |
| `https://developer.android.com/reference/java/lang/IllegalStateException` | if not all the elements can be added at this time due to insertion restrictions |
| `https://developer.android.com/reference/java/lang/NullPointerException` | if the specified collection contains a null element and this queue does not permit null elements, or if the specified collection is null |

**See also:**

- `https://developer.android.com/reference/java/util/AbstractQueue#add(E)`

### clear

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

```
public void clear ()
```

Removes all of the elements from this queue. The queue will be empty after this call returns.

This implementation repeatedly invokes `https://developer.android.com/reference/java/util/Queue#poll()` until it returns `null`.

<br />

### element

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

```
public E element ()
```

Retrieves, but does not remove, the head of this queue. This method differs from `https://developer.android.com/reference/java/util/Queue#peek()` only in that it throws an exception if this queue is empty.

This implementation returns the result of `peek` unless the queue is empty.

<br />

| Returns ||
|---|---|
| `E` | the head of this queue <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/util/NoSuchElementException` | if this queue is empty |

### remove

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

```
public E remove ()
```

Retrieves and removes the head of this queue. This method differs from `https://developer.android.com/reference/java/util/Queue#poll()` only in that it throws an exception if this queue is empty.

This implementation returns the result of `poll` unless the queue is empty.

<br />

| Returns ||
|---|---|
| `E` | the head of this queue <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/util/NoSuchElementException` | if this queue is empty |