Week 9

Question 1

What is the Java Collections Framework?

Answer 1

A framework in Java for storing and manipulating groups of objects

Provides interfaces, implementations, and algorithms for common data structures and collections

Question 2

What are the core interfaces in the Collections Framework?

Answer 2

Collection<E>: A group of objects (elements)</E>

Map<K, V>: A mapping of keys to values

Question 3

What is the Collection<E> interface?</E>

Answer 3

Methods include:

Size and emptiness checks: size(), isEmpty()

Membership operations: contains(Object), add(E), remove(Object)

Bulk operations: addAll(Collection), removeAll(Collection), retainAll(Collection)

Array conversions: toArray()

Question 4

What are the key characteristics of a Set<E>?</E>

Answer 4

No duplicate elements

Common implementations:

HashSet<E>: Unordered, fast operations</E>

TreeSet<E>: Elements are sorted, slower than HashSet</E>

LinkedHashSet<E>: Maintains insertion order</E>

Question 5

What are the characteristics of a List<E>?</E>

Answer 5

Ordered collection, allows duplicate elements

Methods for positional access: get(int index), add(int index, E), remove(int index)

Iteration support via ListIterator

Question 6

What are the main implementations of List<E>?</E>

Answer 6

ArrayList<E>: Backed by a dynamically resizing array, fast random access</E>

LinkedList<E>: Doubly linked list, better for frequent insertions/removals</E>

Question 7

What is a Queue<E>?</E>

Answer 7

Collection for processing elements, typically in first-in-first-out (FIFO) order

Methods:

Add elements: add(E), offer(E)

Access head: peek(), poll(), remove()

Question 8

What is a Deque<E>?</E>

Answer 8

Double-ended queue, allows insertions and deletions at both ends

Examples: ArrayDeque, LinkedList (as a Deque)

Question 9

What is a Map<K, V>?

Answer 9

Maps keys to values; each key maps to at most one value

Methods include:

Basic operations: put(K, V), get(Object), remove(Object)

Bulk operations: putAll(Map), clear()

Views: keySet(), values(), entrySet()

Question 10

What are the main implementations of Map<K, V>?

Answer 10

HashMap<K, V>: Unordered, fast operations

TreeMap<K, V>: Keys sorted in natural or custom order

LinkedHashMap<K, V>: Maintains insertion order

Question 11

What is an Iterator<E>?</E>

Answer 11

Used to traverse a collection.
Methods:

hasNext(): Checks if the next element exists

next(): Retrieves the next element

remove(): Removes the last element returned by next()

Question 12

What is a ListIterator<E>?</E>

Answer 12

Extends Iterator with bi-directional traversal:

hasPrevious(), previous().

add(E), set(E).

Question 13

What are the advantages of using the Java Collections Framework?

Answer 13

Simplifies programming by providing ready-to-use data structures

Ensures type safety with generics

Improves performance with optimized implementations

Question 14

What should you know about the order and uniqueness in collections?

Answer 14

Set: No duplicates, unordered or ordered based on implementation

List: Allows duplicates, ordered

Queue: FIFO or based on other policies, allows duplicates

Map: No duplicate keys, values can be duplicated

Question 15

What is Java Reflection?

Answer 15

The ability of a class or object to examine and manipulate itself

Enables accessing constructors, methods, and fields at runtime

Allows modifying private fields, invoking methods, and constructing new objects dynamically

Question 16

What package supports Reflection in Java?

Answer 16

The java.lang.reflect package

Question 17

How does Reflection interact with Java security?

Answer 17

The JVM’s security manager restricts Reflection to prevent unauthorized access to private fields or methods

Privileges can be granted in specific scenarios (e.g., IDE debugging)

Question 18

What is the entry point for Reflection in Java?

Answer 18

The java.lang.Class object:

Immutable instance created by the JVM for every object type

Provides methods to query object properties and create new objects

Question 19

How can you get a Class object?

Answer 19

Using getClass() on an object instance:

Class<?> c = obj.getClass();

Using .class on a type:

Class<?> c = int.class;

Using Class.forName(String) with a fully qualified name:

Class<?> c = Class.forName(“java.lang.String”);

Question 20

What are some key methods in the Class object?

Answer 20

getFields(): Public fields, including inherited ones

getDeclaredFields(): All fields, irrespective of access modifiers, excluding inherited ones

getMethods(): Public methods, including inherited ones

getDeclaredMethods(): All methods, irrespective of access modifiers, excluding inherited ones

getConstructors(): Public constructors.
getDeclaredConstructors(): All constructors, including private ones

Question 21

How are objects instantiated reflectively?

Answer 21

Two methods are commonly used:

Class.newInstance():

Invokes no-argument constructor.

Requires the constructor to be visible.

Constructor.newInstance():

Can invoke any constructor, including private ones (if allowed)

Preferred method

Question 22

What is AccessibleObject.setAccessible()?

Answer 22

Temporarily overrides JVM security to allow access to private members

Usage depends on the security manager and JVM policy

Question 23

What are the limitations and risks of Reflection?

Answer 23

Performance overhead: Reflective operations are slower than direct calls

Security concerns: Reflection can access private fields and methods

Compatibility issues: Reflective code may break with JVM upgrades

Potential side effects: May render code non-portable and dysfunctional

Question 24

What are common use cases for Reflection?

Answer 24

Debugging: Inspecting running programs

Testing: Forcing specific states or ensuring code coverage

Frameworks: Dynamically handling objects and classes

Question 25

What are the performance considerations for Reflection?

Answer 25

Reflective operations should be avoided in performance-sensitive code due to their slower execution compared to non-reflective counterparts