A PriorityQueue is a list that always keeps its items sorted based on some rule, like smallest to largest. So, when you take an item out, you always get the one with the highest (or lowest) priority.

Data comes in many shapes and forms (obviously), but two of its core ‘structures’ are stacks and queues. Data elements in a stack and a queue differ by virtue of their order.

In contrast, a data structure is a concrete implementation of one or more ADTs, similar to how Java classes implement interfaces. ... Using the Adapter pattern for stacks and queues (DequeStack.java) ...