Add fresher-qa module: 50 Java interview questions for freshers, one runnable demo each, asserted transcripts, javac error captures

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b5DfjBGLBr7F5km2AN

fresher-qa/output/04-collections.txt

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+=== Q28 The Collections Framework hierarchy ===
+ArrayList extends AbstractList implements [List, RandomAccess, Cloneable, Serializable]
+LinkedList extends AbstractSequentialList implements [List, Deque, Cloneable, Serializable]
+HashSet extends AbstractSet implements [Set, Cloneable, Serializable]
+TreeSet extends AbstractSet implements [NavigableSet, Cloneable, Serializable]
+ArrayDeque extends AbstractCollection implements [Deque, Cloneable, Serializable]
+HashMap extends AbstractMap implements [Map, Cloneable, Serializable]
+TreeMap extends AbstractMap implements [NavigableMap, Cloneable, Serializable]
+=== Q29 ArrayList vs LinkedList ===
+ArrayList is RandomAccess:  true
+LinkedList is RandomAccess: false
+LinkedList is also a Deque: true
+after add(0, 5): [5, 10, 20, 30], get(2) = 20
+=== Q30 How HashMap works internally ===
+Aa: hashCode=2112, bucket (16 slots)=0
+BB: hashCode=2112, bucket (16 slots)=0
+Ankur: hashCode=63412443, bucket (16 slots)=12
+both survive a collision: first, second, size 2
+=== Q31 HashMap vs Hashtable vs ConcurrentHashMap vs TreeMap ===
+HashMap: null key accepted
+Hashtable: null key throws NullPointerException
+ConcurrentHashMap: null key throws NullPointerException
+TreeMap: null key throws NullPointerException
+=== Q32 HashSet vs LinkedHashSet vs TreeSet ===
+HashSet       [banana, apple, cherry, pear, mango]
+LinkedHashSet [pear, apple, mango, banana, cherry]
+TreeSet       [apple, banana, cherry, mango, pear]
+=== Q33 Comparable vs Comparator ===
+natural (Comparable):  [Student[name=Asha, marks=88], Student[name=Meena, marks=88], Student[name=Ravi, marks=90]]
+marks desc, then name: [Student[name=Ravi, marks=90], Student[name=Asha, marks=88], Student[name=Meena, marks=88]]
+=== Q34 Fail-fast iterators and ConcurrentModificationException ===
+removing 2 inside for-each -> ConcurrentModificationException
+removing the second-to-last element threw nothing, list = [1, 2, 4]
+removeIf even -> [1, 3, 5]
+=== Q35 Arrays.asList() and List.of() pitfalls ===
+write-through to the array: changed
+Arrays.asList().add -> UnsupportedOperationException
+Arrays.asList(int[]) has 1 element
+List.of(.., null) -> NullPointerException
+=== Q36 Queue, Deque and PriorityQueue ===
+PriorityQueue polls: 1 2 3 4 5
+ArrayDeque as a stack pops: cba
+=== Q37 Mutable keys and the equals()/hashCode() contract in a HashMap ===
+get with the mutated key: null
+get with a fresh "A1" key: null
+size is still 1
+=== Q38 unmodifiableList() view vs List.copyOf() snapshot ===
+view sees the change: [a, b, c]
+copy does not:        [a, b]