![A binary min-heap with 1 at the root, 2 and 8 as its children, and 5 and 3 as the children of 2, next to the backing array [1, 2, 8, 5, 3] with indexes 0 to 4. toString() and the iterator read the array in that order, while calling poll() until the queue is empty returns 1, 2, 3, 5, 8.](/sitelet?url=https%3A%2F%2Fhowtodoinjava.com%2Fwp-content%2Fuploads%2F2026%2F10%2Fjava-priorityqueue-binary-heap-array-order-768x432.png)
A Java priority queue (java.util.PriorityQueue) always returns the smallest element first, or the first element by a Comparator. Learn natural and custom order, max-heaps, ties and why a printed queue looks unsorted.
UnsupportedOperationException is an unchecked exception that lists from Arrays.asList(), List.of() or Stream.toList() throw when the code changes them. Learn the causes, how to read the stack trace and how to fix it with a modifiable copy.
In Java, all types of enumerations and iterators (such as Iterator, ListIterator, SplitIterator) are simply navigational cursors and the main purpose of these cursors is to iterate over the elements of the collection. Each cursor has its own features, advantages and disadvantages. In this article, we will walk through these …
The new sequenced collection interfaces allow adding, retrieving, and removing elements at either end of the collection, along with a reverse-ordered view of it.
Learn the Java ConcurrentSkipListMap and the major differences between ConcurrentSkipListMap and other Map implementations.
java.lang.UnsupportedOperationException means the code tried to change a collection that cannot be changed, such as one from Arrays.asList(), List.of() or Collections.unmodifiableMap(). Copy the data into an ArrayList or HashMap to fix it.
Learn about Java ArrayDeque and its features with practical examples. Learn to use it as Stack and Queue, and the difference from LinkedList.
Java SynchronousQueue is a specific type of BlockingQueue with no internal capacity and is primarily used in exchanging data between two threads.
Learn Queue data structure and the Java Queue interface and implementations with practical examples such as LinkedList, PriorityQueue and ArrayDeque.
Learn to create a List from array using Arrays.asList(array) and new ArrayList(Arrays.asList(array). Learn their differences with examples.
A collection is a group of objects. Java Collections framework consists of classes and interfaces to work with lists, sets, maps and queues.
This Java guide will take us through Java Collections framework. We will understand the core concepts and performing the basic operations.
A submap is a portion or part of a map between the keys of a specific range. Learn how to get submap from map in Java with different ways.
A nested Map is Map inside another Map. Learn to create a nested HashMap and add, remove and iterate over the elements with examples.
Learn to use BlockingQueue drainTo() method for draining the queue items (polling all or specific number of elements) into a Collection.
IdentityHashMap implements the Map interface and has almost the same features as HashMap. It uses reference equality on key search operations.
ConcurrentMap is an interface in Java Collections and used to create a thread-safe Maps. It stores the key-value pairs in a synchronized way.
CopyOnWriteArraySet is a thread-safe Set in Java. It ensures safe concurrent access by creating a new copy of the internal array for each modification.
Java CopyOnWriteArrayList is a thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array. It’s immutable snapshot style iterator method uses a reference to the state of the array at the point that the iterator …
In Java, the TransferQueue interface is a concurrent BlockingQueue implementation with support to support “synchronous message passing” between producers and consumers. The key feature of TransferQueue is the transfer() method that blocks until the message is handed off to a consumer. 1. TransferQueue Interface The TransferQueue is an interface in …
ArrayBlockingQueue class is Java concurrent and bounded blocking queue implementation backed by an array. It orders elements FIFO (first-in-first-out). The head of the ArrayBlockingQueue is that element that has been on the queue the longest time. The tail of the ArrayBlockingQueue is that element that has been on the queue …
Java PriorityBlockingQueue class is concurrent blocking queue data structure implementation in which objects are processed based on their priority. The “blocking” part of the name is added to imply the thread will block waiting until there’s an item available on the queue.
Java PriorityQueue is an unbounded Queue implementation that processes the items based on priorities. Custom ordering can be enforced with a Comparator.
Unlike traditional iterators, Spliterator is designed with parallelism in mind and mainly helps in parallel processing when the collection or stream has a large number of elements.
Java TreeMap class stores key-value pairs very similar to the HashMap class. The difference is that TreeMap provides an efficient way to store key/value pairs in sorted order. The TreeMap class is a red-black tree-based NavigableMap implementation. This Java TreeMap tutorial will teach us about TreeMap class, methods, usecases, and …
Learn to create a Java List with only one element in it using Arrays.asList() and Collections.singletonList() methods.
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