Java DSA basics

Common data structures in Java

• ArrayList<T> for dynamic arrays
• LinkedList<T> for list and queue operations
• HashMap<K,V> for lookup by key
• HashSet<T> for unique data
• Queue<T> and Deque<T> for FIFO and stack-like behavior
• PriorityQueue<T> for heap-based ordering
• TreeSet<T> and TreeMap<K,V> for ordering
• Arrays.sort() for sorting arrays
• Collections.sort() for lists

Java interview rule

Use the correct collection for the problem. For example:

• fast lookup → HashMap
• sorted order → TreeMap or TreeSet
• queue behavior → Queue / Deque
• top-K → PriorityQueue