Working with Arrays & Collections Summary

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title: "Working with Arrays & Collections Summary" date: "2024-08-16" excerpt: "A quick-reference summary for arrays, collections, generics, sorting/searching, null behavior, and comparators in Java."

tags: "java,collections,arrays" source: "https://shrikant-havale.in/2024/08/16/working-with-arrays-collections-summary/"

This is a focused summary of practical Java collection and array behavior.

Deque Notes

• ArrayDeque is a Deque implementation.
• Useful operations:
  • Add to tail: offer, offerLast
  • Read head: peek, peekFirst
  • Push front: push, offerFirst, addFirst
  • Remove head: poll, pop, removeFirst
  • Remove tail: removeLast

Arrays

• With {...} initializer, size is inferred.
• Without initializer, size is required.
• Arrays.sort(...) and Arrays.binarySearch(...) are standard methods.
• binarySearch expects correctly sorted input.
• Arrays.mismatch(a, b) returns first differing index, or -1 if equal.

Generics and Wildcards

• ? wildcard is valid in declarations but not when instantiating concrete types on RHS.
• Always prefer explicit type parameters on declarations.
• Diamond operator <> helps avoid duplicate type declarations.

Collections

• Map is part of the Collections Framework but does not implement Collection.
• Collections.binarySearch(...) requires matching sort order and comparator.

Null Handling

• TreeSet rejects null due to comparison requirements.
• HashSet allows one null.
• ArrayList and LinkedList allow multiple null values.

Comparable vs Comparator

• Comparable<T> => implement compareTo(T).
• Comparator<T> => implement compare(T, T).
• Comparator chains and reversals (reversed()) are useful for custom sort logic.

Immutable Factories

• List.of(...), Set.of(...) => immutable collections from values.
• List.copyOf(...), Set.copyOf(...) => immutable copies.

Source

Original post: https://shrikant-havale.in/2024/08/16/working-with-arrays-collections-summary/