Java Collections

Question 1

What is a collection?

Answer 1

An object that groups multiple elements into a single unit.
Poker hand: collection of cards
Mail folder: collection of letters.

Question 2

Collection vs Map

Answer 2

Collection - a group of objects known as elements
public interface Collection
Map - a group of objects where each object maps keys to values
public interface Map

Question 3

How do you iterate over a collection

Answer 3

For-each notation,

need an iterator object if you want to safely remove elements while iterating.

Question 4

What is the Set interface?

Answer 4

Extends collection, a set contains no duplicate elements. 2 sets are equal if they contain the same elements even if the containers are different.

Question 5

What is the List interface?

Answer 5

A list is an ordered collection of elements that may contain duplicate elements. Two lists are treated equal if they contain the same elements in the same order.

Question 6

Concrete List implementation in Java

Answer 6

ArrayList

LinkedList

Question 7

What is a Queue interface?

Answer 7

Collection of elements stored for processing first in first out.

Question 8

What is a map interface?

Answer 8

2 generic type arguments where keys are mapped to value each key maps to at most one value.