What is PriorityQueue in Java?
Why Interviewers Ask This
This question targets practical, hands-on experience with Java. Interviewers want to see if you've worked with these concepts in real projects, not just read about them. Strong answers include concrete examples.
Answer
A PriorityQueue is a queue where elements are ordered by their natural ordering (if they implement Comparable) or by a provided Comparator, not by insertion order. The head of the queue is always the smallest element (min-heap by default). Operations: offer() adds an element (O(log n)), poll() removes and returns the head (O(log n)), peek() returns the head without removing (O(1)). PriorityQueue does not permit null elements. Iteration over a PriorityQueue does not guarantee any particular order — only the head is guaranteed to be the minimum. Use it for scheduling algorithms, Dijkstra's shortest path, and any problem requiring "process the most important item first" semantics.
Common Mistake
Don't just define the term — demonstrate that you understand when to use it and when not to. Showing awareness of trade-offs is what separates average from strong Java candidates.
More Java Questions
View all →- Intermediate What is the Java Collections Framework?
- Intermediate What is the difference between ArrayList and LinkedList?
- Intermediate What is HashMap in Java and how does it work internally?
- Intermediate What is the difference between HashMap and HashTable in Java?
- Intermediate What is the difference between HashMap and LinkedHashMap?