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Java Data Structures Cheatsheet PDF | Arrays, Lists, Maps, Trees Reference

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Highlights

  • Digital download

Covers the Java collections and syntax that come up in ICS4U, AP CS A, and first-year university CS. Each entry has the actual code, the time complexity, and the thing that trips people up.

What's included:
- Arrays: declare and initialize, 2D arrays, Arrays.sort(), Arrays.copyOf()
- ArrayList: create, add/get/size, remove by index vs remove by value, Collections.sort()
- Stack and Queue: ArrayDeque (preferred over the legacy Stack class), Queue with LinkedList, PriorityQueue for min-heap
- HashMap and HashSet: put/get/containsKey, getOrDefault() to avoid NullPointerException, iterating with entrySet()
- LinkedList, TreeMap (sorted keys), TreeSet (sorted unique elements), custom BST node
- Common mistakes: arr.length vs list.size(), ArrayList<int> vs ArrayList<Integer>, why ArrayDeque beats the Stack class
- Quick decision guide: when to use ArrayList vs ArrayDeque vs HashMap

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Listed on 07 Aug, 2026
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