Collections Interview Questions

General Questions

1.    What is a Collections Framework ? What are the benefits of Java Collections Framework?

2.    What is the difference between Collection and Collections ?

3.    What is the difference between List, Set and Map?

4.    What is Iterator?

5.    How to avoid concurrentModificationException when using an iterator?

6.    Difference between fail-fast and fail-safe?

7.    What does the hashCode() method?

8.    Why we override equals() method?

9.    Explain Collection’s hierarchy?

10. Difference between Comparable and Comparator interface?

List Interface Releated

1.    Difference between ArrayList and CopyOnWriteArrayList?

2.    Difference between ArrayList and LinkedList?

3.    Can we store duplicate values in List?

4.    How to remove duplicate values from List?

5.    Difference between iterator and listIterator?

6.    Difference Between iterator and Enumaration?

7.    Difference between Array and ArrayList?

8.    How to remove a value from list?

9.    How to sort ArrayList in descending order?

10. how does the size increases in arraylist?

Set Interface Releated

1.    How HashSet works in java?

2.    Difference between HashSet, LinkedHashSet and TreeSet?

3.    Can we store duplicate values in Set?

4.    How to eliminate duplicate user defined objects in HashSet?

5.    If we try to store duplicate values in a “Set”, what will happen? Do we get any complier error?

6.    How to sort the list of user defined objects in HashSet?

7.    Is HashSet thread safe in Java?

8.    How to remove a value from set?

Map Interface Releated

1.    Difference between HashMap, ConcurrentHashMap and SynchronizedHashMap?

2.    Difference between HashMap, LinkedHashMap and TreeMap?

3.    Difference between HashMap and HashTable?

4.    How HashMap works internally in java?

5.    How to iterate HashMap in java?

6.    Can we store custom object to key attribute of HashMap?

7.    Does the Hashmap allow duplicate key or how Hashmap finds duplicate key ?

8.    Can we store null key in HashMap?

9.    How to preserve insertion order in HashMap?

10. Is HashMap thread safe in java?

11. What happens if two threads perform a get of one hashmap at the same time?

12. How to Sort HashMap in Java based on Keys and Values?


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