Java : PriorityBlockingQueue with Examples

PriorityBlockingQueue (Java SE 20 & JDK 20) API Examples.
You will find code examples on most PriorityBlockingQueue methods.

Summary

An unbounded blocking queue that uses the same ordering rules as class PriorityQueue and supplies blocking retrieval operations. While this queue is logically unbounded, attempted additions may fail due to resource exhaustion (causing OutOfMemoryError).

Class diagram

final long current = System.nanoTime();
final DoubleSupplier elapsedTime = () -> (System.nanoTime() - current) / 1000000000.0;

try (final var executor = Executors.newSingleThreadExecutor()) {

    final var queue = new PriorityBlockingQueue<String>();

    final var future = executor.submit(() -> {
        try {
            while (true) {
                System.out.println("  take ...");
                final var value = queue.take();

                System.out.printf("  take OK! : value = %s (%f sec.)%n",
                        value, elapsedTime.getAsDouble());
            }
        } catch (InterruptedException e) {
            System.out.println("  InterruptedException!");
        }
    });

    System.out.printf("put values (%f sec.)%n", elapsedTime.getAsDouble());

    queue.put("aaa");
    queue.put("bbb");
    queue.put("ccc");

    TimeUnit.SECONDS.sleep(5);

    System.out.printf("put values (%f sec.)%n", elapsedTime.getAsDouble());

    queue.put("XXX");
    queue.put("YYY");
    queue.put("ZZZ");

    TimeUnit.SECONDS.sleep(5);

    System.out.println("future.cancel");
    future.cancel(true);
}

// Result
// ↓
//put values (0.002364 sec.)
//  take ...
//  take OK! : value = aaa (0.004022 sec.)
//  take ...
//  take OK! : value = bbb (0.004228 sec.)
//  take ...
//  take OK! : value = ccc (0.004420 sec.)
//  take ...
//put values (5.009203 sec.)
//  take OK! : value = XXX (5.009556 sec.)
//  take ...
//  take OK! : value = YYY (5.009790 sec.)
//  take ...
//  take OK! : value = ZZZ (5.009974 sec.)
//  take ...
//future.cancel
//  InterruptedException!

record Item(String value, int priority) {
    @Override
    public String toString() {
        return "%s(%d)".formatted(value, priority);
    }
}

final var comparator = Comparator.comparingInt(Item::priority);

final var queue = new PriorityBlockingQueue<Item>(11, comparator);
System.out.println(queue); // []

System.out.println(queue.offer(new Item("aaa", 1))); // true
System.out.println(queue.offer(new Item("bbb", 2))); // true
System.out.println(queue.offer(new Item("ccc", 3))); // true
System.out.println(queue.offer(new Item("XXX", 100))); // true
System.out.println(queue.offer(new Item("YYY", 99))); // true
System.out.println(queue.offer(new Item("ZZZ", 98))); // true

System.out.println(queue); // [aaa(1), bbb(2), ccc(3), XXX(100), YYY(99), ZZZ(98)]

System.out.println(queue.poll()); // aaa(1)
System.out.println(queue.poll()); // bbb(2)
System.out.println(queue.poll()); // ccc(3)
System.out.println(queue.poll()); // ZZZ(98)
System.out.println(queue.poll()); // YYY(99)
System.out.println(queue.poll()); // XXX(100)

Constructors

PriorityBlockingQueue ()

Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []
System.out.println(queue.remainingCapacity()); // 2147483647

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, bbb, ccc]

PriorityBlockingQueue (int initialCapacity)

Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering.

final var queue = new PriorityBlockingQueue<Integer>(10000000);
System.out.println(queue); // []

final var startTime = System.nanoTime();

for (int i = 0; i < 4000000; i++) {
    queue.add(i);
}

final var endTime = System.nanoTime();

// 0.197829 sec.
System.out.printf("%f sec.%n", (endTime - startTime) / 1000000000.0);

final var queue = new PriorityBlockingQueue<Integer>(1);
System.out.println(queue); // []

final var startTime = System.nanoTime();

for (int i = 0; i < 4000000; i++) {
    queue.add(i);
}

final var endTime = System.nanoTime();

// 0.262046 sec.
System.out.printf("%f sec.%n", (endTime - startTime) / 1000000000.0);

Note that capacity in initialCapacity and remainingCapacity() have different meanings.

final var queue = new PriorityBlockingQueue<Integer>(100);
System.out.println(queue.remainingCapacity()); // 2147483647

PriorityBlockingQueue (int initialCapacity, Comparator<? super E> comparator)

Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.

Please see also PriorityBlockingQueue(int initialCapacity) for initialCapacity parameter.

record Item(String value, int priority) {
    @Override
    public String toString() {
        return "%s(%d)".formatted(value, priority);
    }
}

final var comparator = Comparator.comparingInt(Item::priority);

final var queue = new PriorityBlockingQueue<Item>(11, comparator);
System.out.println(queue); // []

System.out.println(queue.offer(new Item("aaa", 1))); // true
System.out.println(queue.offer(new Item("bbb", 2))); // true
System.out.println(queue.offer(new Item("ccc", 3))); // true
System.out.println(queue.offer(new Item("XXX", 100))); // true
System.out.println(queue.offer(new Item("YYY", 99))); // true
System.out.println(queue.offer(new Item("ZZZ", 98))); // true

System.out.println(queue); // [aaa(1), bbb(2), ccc(3), XXX(100), YYY(99), ZZZ(98)]

System.out.println(queue.poll()); // aaa(1)
System.out.println(queue.poll()); // bbb(2)
System.out.println(queue.poll()); // ccc(3)
System.out.println(queue.poll()); // ZZZ(98)
System.out.println(queue.poll()); // YYY(99)
System.out.println(queue.poll()); // XXX(100)

PriorityBlockingQueue (Collection<? extends E> c)

Creates a PriorityBlockingQueue containing the elements in the specified collection.

final var c = List.of("a", "b", "c");

final var queue = new PriorityBlockingQueue<>(c);
System.out.println(queue); // [a, b, c]
System.out.println(queue.size()); // 3

Methods

boolean add (E e)

Inserts the specified element into this priority queue.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []

System.out.println(queue.add("aaa")); // true
System.out.println(queue); // [aaa]

System.out.println(queue.add("bbb")); // true
System.out.println(queue); // [aaa, bbb]

System.out.println(queue.add("ccc")); // true
System.out.println(queue); // [aaa, bbb, ccc]

void clear ()

Atomically removes all of the elements from this queue.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []

System.out.println(queue.offer("a")); // true
System.out.println(queue); // [a]

System.out.println(queue.offer("b")); // true
System.out.println(queue); // [a, b]

queue.clear();
System.out.println(queue); // []

Comparator<? super E> comparator ()

Returns the comparator used to order the elements in this queue, or null if this queue uses the natural ordering of its elements.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []

final var comparator = queue.comparator();
System.out.println(comparator); // null

final var queue = new PriorityBlockingQueue<String>(11, Comparator.reverseOrder());
System.out.println(queue); // []

final var comparator = queue.comparator();
System.out.println(Objects.equals(comparator, Comparator.reverseOrder())); // true

final var queue = new PriorityBlockingQueue<>(11, String.CASE_INSENSITIVE_ORDER);
System.out.println(queue); // []

final var comparator = queue.comparator();
System.out.println(Objects.equals(comparator, String.CASE_INSENSITIVE_ORDER)); // true

boolean contains (Object o)

Returns true if this queue contains the specified element.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, bbb, ccc]

System.out.println(queue.contains("aaa")); // true
System.out.println(queue.contains("bbb")); // true
System.out.println(queue.contains("XXX")); // false

int drainTo (Collection<? super E> c)

Removes all available elements from this queue and adds them to the given collection.

final var queue = new PriorityBlockingQueue<String>();
final var c = new ArrayList<String>();

System.out.println(queue.offer("aaa")); // true

System.out.println(queue); // [aaa]
System.out.println(c); // []

System.out.println(queue.drainTo(c)); // 1

System.out.println(queue); // []
System.out.println(c); // [aaa]

System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [bbb, ccc]
System.out.println(c); // [aaa]

System.out.println(queue.drainTo(c)); // 2

System.out.println(queue); // []
System.out.println(c); // [aaa, bbb, ccc]

int drainTo (Collection<? super E> c, int maxElements)

Removes at most the given number of available elements from this queue and adds them to the given collection.

final var queue = new PriorityBlockingQueue<String>();
final var c = new ArrayList<String>();

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, bbb, ccc]
System.out.println(c); // []

System.out.println(queue.drainTo(c, 10)); // 3

System.out.println(queue); // []
System.out.println(c); // [aaa, bbb, ccc]

System.out.println(queue.offer("XXX")); // true
System.out.println(queue.offer("YYY")); // true
System.out.println(queue.offer("ZZZ")); // true

System.out.println(queue); // [XXX, YYY, ZZZ]
System.out.println(c); // [aaa, bbb, ccc]

System.out.println(queue.drainTo(c, 2)); // 2

System.out.println(queue); // [ZZZ]
System.out.println(c); // [aaa, bbb, ccc, XXX, YYY]

void forEach (Consumer<? super E> action)

Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, bbb, ccc]

System.out.println("-- forEach --");
queue.forEach(value -> {
    System.out.println("value = " + value);
});

// Result
// ↓
//-- forEach --
//value = aaa
//value = bbb
//value = ccc

Iterator<E> iterator ()

Returns an iterator over the elements in this queue.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, bbb, ccc]

final var iterator = queue.iterator();

System.out.println("-- forEachRemaining --");
iterator.forEachRemaining(value -> {
    System.out.println("value = " + value);
});

// Result
// ↓
//-- forEachRemaining --
//value = aaa
//value = bbb
//value = ccc

boolean offer (E e)

Inserts the specified element into this priority queue.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []

System.out.println(queue.offer("aaa")); // true
System.out.println(queue); // [aaa]

System.out.println(queue.offer("bbb")); // true
System.out.println(queue); // [aaa, bbb]

System.out.println(queue.offer("ccc")); // true
System.out.println(queue); // [aaa, bbb, ccc]

boolean offer (E e, long timeout, TimeUnit unit)

Inserts the specified element into this priority queue.

Please see also : offer(E e)

As the queue is unbounded, this method will never block.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []
System.out.println(queue.remainingCapacity()); // 2147483647

System.out.println(queue.offer("aaa", 10, TimeUnit.SECONDS)); // true
System.out.println(queue); // [aaa]

System.out.println(queue.offer("bbb", 10, TimeUnit.SECONDS)); // true
System.out.println(queue); // [aaa, bbb]

E peek ()

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue.peek()); // aaa
System.out.println(queue); // [aaa, bbb, ccc]

System.out.println(queue.poll()); // aaa
System.out.println(queue); // [bbb, ccc]

System.out.println(queue.peek()); // bbb
System.out.println(queue); // [bbb, ccc]

System.out.println(queue.poll()); // bbb
System.out.println(queue); // [ccc]

System.out.println(queue.peek()); // ccc
System.out.println(queue); // [ccc]

System.out.println(queue.poll()); // ccc
System.out.println(queue); // []

System.out.println(queue.peek()); // null
System.out.println(queue); // []

E poll ()

Retrieves and removes the head of this queue, or returns null if this queue is empty.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, bbb, ccc]

System.out.println(queue.poll()); // aaa
System.out.println(queue); // [bbb, ccc]

System.out.println(queue.poll()); // bbb
System.out.println(queue); // [ccc]

System.out.println(queue.poll()); // ccc
System.out.println(queue); // []

System.out.println(queue.poll()); // null
System.out.println(queue); // []

E poll (long timeout, TimeUnit unit)

Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.

Please see also : poll()

final long current = System.nanoTime();
final DoubleSupplier elapsedTime = () -> (System.nanoTime() - current) / 1000000000.0;

try (final var executor = Executors.newSingleThreadExecutor()) {

    final var queue = new PriorityBlockingQueue<String>();

    final var future = executor.submit(() -> {
        try {
            while (true) {
                System.out.println("  poll ...");
                final var value = queue.poll(5, TimeUnit.SECONDS);

                System.out.printf("  poll value = %s (%f sec.)%n",
                        value, elapsedTime.getAsDouble());
            }
        } catch (InterruptedException e) {
            System.out.println("  InterruptedException!");
        }
    });

    System.out.printf("put values (%f sec.)%n", elapsedTime.getAsDouble());

    queue.put("aaa");
    queue.put("bbb");
    queue.put("ccc");

    TimeUnit.SECONDS.sleep(8);

    System.out.println("future.cancel");
    future.cancel(true);
}

// Result
// ↓
//put values (0.002233 sec.)
//  poll ...
//  poll value = aaa (0.003545 sec.)
//  poll ...
//  poll value = bbb (0.003715 sec.)
//  poll ...
//  poll value = ccc (0.003865 sec.)
//  poll ...
//  poll value = null (5.013690 sec.)
//  poll ...
//future.cancel
//  InterruptedException!

void put (E e)

Inserts the specified element into this priority queue.

As the queue is unbounded, this method will never block.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []
System.out.println(queue.remainingCapacity()); // 2147483647

queue.put("aaa");
System.out.println(queue); // [aaa]

queue.put("bbb");
System.out.println(queue); // [aaa, bbb]

int remainingCapacity ()

Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.

final var queue = new PriorityBlockingQueue<String>();
System.out.println(queue); // []

final var capacity = queue.remainingCapacity();
System.out.println(capacity); // 2147483647
System.out.println(capacity == Integer.MAX_VALUE); // true

System.out.println(queue.offer("aaa")); // true

System.out.println(queue); // [aaa]
System.out.println(queue.remainingCapacity()); // 2147483647

System.out.println(queue.offer("bbb")); // true

System.out.println(queue); // [aaa, bbb]
System.out.println(queue.remainingCapacity()); // 2147483647

boolean remove (Object o)

Removes a single instance of the specified element from this queue, if it is present.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, aaa, bbb, bbb, ccc]

System.out.println(queue.remove("aaa")); // true
System.out.println(queue); // [aaa, bbb, bbb, ccc]

System.out.println(queue.remove("bbb")); // true
System.out.println(queue); // [aaa, ccc, bbb]

System.out.println(queue.remove("bbb")); // true
System.out.println(queue); // [aaa, ccc]

System.out.println(queue.remove("XXX")); // false
System.out.println(queue); // [aaa, ccc]

boolean removeAll (Collection<?> c)

Removes all of this collection's elements that are also contained in the specified collection (optional operation).

final var src = List.of("a", "b", "a", "b", "A", "B");
System.out.println(src); // [a, b, a, b, A, B]

{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.removeAll(List.of())); // false
    System.out.println(queue); // [A, a, B, b, b, a]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.removeAll(List.of("a"))); // true
    System.out.println(queue); // [A, B, b, b]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.removeAll(List.of("a", "b"))); // true
    System.out.println(queue); // [A, B]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.removeAll(List.of("b", "a"))); // true
    System.out.println(queue); // [A, B]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.removeAll(List.of("A"))); // true
    System.out.println(queue); // [B, a, b, b, a]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.removeAll(List.of("X", "Y", "Z"))); // false
    System.out.println(queue); // [A, a, B, b, b, a]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.removeAll(List.of("A", "X", "Y", "Z"))); // true
    System.out.println(queue); // [B, a, b, b, a]
}

boolean removeIf (Predicate<? super E> filter)

Removes all of the elements of this collection that satisfy the given predicate.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("BBB")); // true
System.out.println(queue.offer("ccc")); // true
System.out.println(queue.offer("DDD")); // true

System.out.println(queue); // [BBB, DDD, ccc, aaa]

final var ret = queue.removeIf(s -> {
    return s.equals(s.toUpperCase());
});

System.out.println(ret); // true
System.out.println(queue); // [aaa, ccc]

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true

System.out.println(queue); // [aaa, bbb]

final var ret = queue.removeIf(s -> s.equals(s.toUpperCase()));

System.out.println(ret); // false
System.out.println(queue); // [aaa, bbb]

boolean retainAll (Collection<?> c)

Retains only the elements in this collection that are contained in the specified collection (optional operation).

final var src = List.of("a", "b", "a", "b", "A", "B");
System.out.println(src); // [a, b, a, b, A, B]

{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.retainAll(List.of())); // true
    System.out.println(queue); // []
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.retainAll(List.of("a", "b"))); // true
    System.out.println(queue); // [a, a, b, b]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.retainAll(List.of("b", "a"))); // true
    System.out.println(queue); // [a, a, b, b]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.retainAll(List.of("A"))); // true
    System.out.println(queue); // [A]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.retainAll(List.of("X", "Y", "Z"))); // true
    System.out.println(queue); // []
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.retainAll(List.of("A", "X", "Y", "Z"))); // true
    System.out.println(queue); // [A]
}
{
    final var queue = new PriorityBlockingQueue<>(src);
    System.out.println(queue); // [A, a, B, b, b, a]

    System.out.println(queue.retainAll(List.of("a", "b", "A", "B"))); // false
    System.out.println(queue); // [A, a, B, b, b, a]
}

int size ()

Returns the number of elements in this collection.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue); // []
System.out.println(queue.size()); // 0

System.out.println(queue.offer("aaa")); // true

System.out.println(queue); // [aaa]
System.out.println(queue.size()); // 1

System.out.println(queue.offer("bbb")); // true

System.out.println(queue); // [aaa, bbb]
System.out.println(queue.size()); // 2

System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, bbb, ccc]
System.out.println(queue.size()); // 3

queue.clear();

System.out.println(queue); // []
System.out.println(queue.size()); // 0

Spliterator<E> spliterator ()

Returns a Spliterator over the elements in this queue.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("aaa")); // true
System.out.println(queue.offer("bbb")); // true
System.out.println(queue.offer("ccc")); // true

System.out.println(queue); // [aaa, bbb, ccc]

final var spliterator = queue.spliterator();

System.out.println("-- forEachRemaining --");
spliterator.forEachRemaining(value -> {
    System.out.println("value = " + value);
});

// Result
// ↓
//-- forEachRemaining --
//value = aaa
//value = bbb
//value = ccc

E take ()

Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

final long current = System.nanoTime();
final DoubleSupplier elapsedTime = () -> (System.nanoTime() - current) / 1000000000.0;

try (final var executor = Executors.newSingleThreadExecutor()) {

    final var queue = new PriorityBlockingQueue<String>();

    final var future = executor.submit(() -> {
        try {
            while (true) {
                System.out.println("  take ...");
                final var value = queue.take();

                System.out.printf("  take OK! : value = %s (%f sec.)%n",
                        value, elapsedTime.getAsDouble());
            }
        } catch (InterruptedException e) {
            System.out.println("  InterruptedException!");
        }
    });

    System.out.printf("put values (%f sec.)%n", elapsedTime.getAsDouble());

    queue.put("aaa");
    queue.put("bbb");
    queue.put("ccc");

    TimeUnit.SECONDS.sleep(5);

    System.out.printf("put values (%f sec.)%n", elapsedTime.getAsDouble());

    queue.put("XXX");
    queue.put("YYY");
    queue.put("ZZZ");

    TimeUnit.SECONDS.sleep(5);

    System.out.println("future.cancel");
    future.cancel(true);
}

// Result
// ↓
//put values (0.002364 sec.)
//  take ...
//  take OK! : value = aaa (0.004022 sec.)
//  take ...
//  take OK! : value = bbb (0.004228 sec.)
//  take ...
//  take OK! : value = ccc (0.004420 sec.)
//  take ...
//put values (5.009203 sec.)
//  take OK! : value = XXX (5.009556 sec.)
//  take ...
//  take OK! : value = YYY (5.009790 sec.)
//  take ...
//  take OK! : value = ZZZ (5.009974 sec.)
//  take ...
//future.cancel
//  InterruptedException!

Object[] toArray ()

Returns an array containing all of the elements in this queue.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("a")); // true
System.out.println(queue.offer("b")); // true
System.out.println(queue.offer("c")); // true

System.out.println(queue); // [a, b, c]

final Object[] array = queue.toArray();
System.out.println(Arrays.toString(array)); // [a, b, c]

<T> T[] toArray (T[] a)

Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array.

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("a")); // true
System.out.println(queue.offer("b")); // true
System.out.println(queue.offer("c")); // true

System.out.println(queue); // [a, b, c]

final String[] array = queue.toArray(new String[0]);
System.out.println(Arrays.toString(array)); // [a, b, c]

final var queue = new PriorityBlockingQueue<String>();

System.out.println(queue.offer("a")); // true
System.out.println(queue.offer("b")); // true
System.out.println(queue.offer("c")); // true

System.out.println(queue); // [a, b, c]

{
    final String[] array = new String[3];
    System.out.println(Arrays.toString(array)); // [null, null, null]

    final var ret = queue.toArray(array);
    System.out.println(Arrays.toString(array)); // [a, b, c]
    System.out.println(Arrays.toString(ret)); // [a, b, c]
}
{
    final String[] array = new String[5];
    System.out.println(Arrays.toString(array)); // [null, null, null, null, null]

    final var ret = queue.toArray(array);
    System.out.println(Arrays.toString(array)); // [a, b, c, null, null]
    System.out.println(Arrays.toString(ret)); // [a, b, c, null, null]
}
{
    final String[] array = new String[1];
    System.out.println(Arrays.toString(array)); // [null]

    final var ret = queue.toArray(array);
    System.out.println(Arrays.toString(array)); // [null]
    System.out.println(Arrays.toString(ret)); // [a, b, c]
}

Methods declared in AbstractQueue

addAll, element, remove

Please see the link below.

Java API Examples : AbstractQueue

Methods declared in AbstractCollection

containsAll, isEmpty, toString

Please see the link below.

Java API Examples : AbstractCollection

Methods declared in Collection

addAll, containsAll, equals, hashCode, isEmpty, parallelStream, stream, toArray

Please see the link below.

Java API Examples : Collection

Methods declared in Queue

element, remove

Please see the link below.

Java API Examples : Queue

Use TimeUnit.sleep instead of Thread.sleep

API Examples

Java : PriorityBlockingQueue with Examples

Summary

Constructors

PriorityBlockingQueue ()

PriorityBlockingQueue (int initialCapacity)

PriorityBlockingQueue (int initialCapacity, Comparator<? super E> comparator)

PriorityBlockingQueue (Collection<? extends E> c)

Methods

boolean add (E e)

void clear ()

Comparator<? super E> comparator ()

boolean contains (Object o)

int drainTo (Collection<? super E> c)

int drainTo (Collection<? super E> c, int maxElements)

void forEach (Consumer<? super E> action)

Iterator<E> iterator ()

boolean offer (E e)

boolean offer (E e, long timeout, TimeUnit unit)

E peek ()

E poll ()

E poll (long timeout, TimeUnit unit)

void put (E e)

int remainingCapacity ()

boolean remove (Object o)

boolean removeAll (Collection<?> c)

boolean removeIf (Predicate<? super E> filter)

boolean retainAll (Collection<?> c)

int size ()

Spliterator<E> spliterator ()

E take ()

Object[] toArray ()

<T> T[] toArray (T[] a)

Methods declared in AbstractQueue

addAll, element, remove

Methods declared in AbstractCollection

containsAll, isEmpty, toString

Methods declared in Collection

addAll, containsAll, equals, hashCode, isEmpty, parallelStream, stream, toArray

Methods declared in Queue

element, remove

Related posts