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Java · Question Set
Strings & Core Collections Essentials interview questions for placements and exams.
Questions
14
Included in this set
Subject
Java
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Difficulty
Mixed
Level of this set
Go through each question and its explanation. Use this set as a focused practice pack for Java.
The pool enables reuse of identical String literals, saving memory and speeding equality checks.
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Safety in sharing/caching (e.g., pool, classpath, keys) and security/thread-safety; also enables stable hash codes for map keys.
StringBuilder is non-synchronized and faster in single-threaded contexts.
equals is overridden to compare character content; == checks object identity.
Collection(List/Set/Queue/Deque) and Map; e.g., ArrayList, HashSet, ArrayDeque, HashMap.
ArrayList random access (O(1)) due to contiguous array; LinkedList insert/remove in middle (O(1) after locating node) due to links.
HashSet (no order), LinkedHashSet (insertion order), TreeSet (sorted).
Consistency ensures keys that are equal hash to same bucket and behave correctly.
TreeMap is sorted (log N ops, Comparable/Comparator needed); HashMap is unsorted (avg O(1) ops) and only needs equals/hashCode.
Fail-fast checks a modCount; external structural changes break the iteration contract.
Comparable defines a natural order in the class itself; Comparator supplies alternative or external orderings without changing the class.
It returns an unmodifiable view that throws on mutating operations.
ArrayList uses a backing array and grows by allocating a larger one then copying.
ConcurrentHashMap avoids a global lock to scale concurrent access; Hashtable and synchronizedMap use coarse-grained locks.