Collections

Question 1

What is the collection framework?

Answer 1

Unified architecture for representing and manipulating collections

Question 2

What are some benefits of the collection framework?

Answer 2

• Reduced programming effort
• Reliable and optimised
• Standard interfaces, so less to learn
• Implementation of each interface interchangable

Question 3

What are the three things that are contained in the collection framework?

Answer 3

Algorithms
Interfaces
Implementation

Question 4

What is a collection?

Answer 4

An object that groups multiple elements into a single element

Question 5

What were the three design goals of the collection framework?

Answer 5

• Produce a reasonably small API (size and conceptual weight)
• Small number of core interfaces
• Only have methods if it is a truly fundamental operation or compelling performance reason

Question 6

Describe the collection interface

Answer 6

• Root interface in the collection hierarchy
• Represents a group of objects
• No direct implementations of this interface

Question 7

Describe the set interface

Answer 7

Collection with no duplicates

Need to be careful if elements are mutable

Question 8

Describe the sorted set interface

Answer 8

Set with a total ordering on elements
Either natural ordering (defined by Comparable) or defined by Comparator
Ordering must be consistent with equals

Question 9

Describe the navigable set interface

Answer 9

Sorted set extended with navigation methods

Example: Retrieve element closest to given element, iterate in ascending or descending order

Question 10

Describe the list interface

Answer 10

An ordered collection
Control over where elements are inserted
Access elements by index
Usually allow duplicates
Specialised iterator

Question 11

Describe the queue interface

Answer 11

Collection for holding elements prior to processing
Typically FIFO
Either throw exception if operation fails or return special value

Question 12

Describe the blocking queue interface

Answer 12

Queue with additional operations that wait if necessary

Question 13

Describe the transfer queue interface

Answer 13

Blocking queue with operations to support transfer of data where producers may wait for consumers to receive elements

Question 14

Describe the Deque interface

Answer 14

Linear collection supporting element insertion and removal at both ends

Question 15

Describe the BlockingDeque interface

Answer 15

Dequeue with additional operations that wait if necessary

Question 16

Describe the Map interface

Answer 16

Mapping from keys to values

No duplicate keys, key maps to at most one value

Question 17

What are the three ways you can view a map?

Answer 17

Set of keys
Collection of values
Set of key-value pairs

Question 18

Describe the Sorted Map interface

Answer 18

Map until total ordering on keys

Natural ordering or defined by Comparator

Question 19

Describe the Navigable Map interface

Answer 19

Sorted map extended with navigation methods

Question 20

Describe the ConcurrentMap interface

Answer 20

Provides thread safety and atomicity guarentees

Example methods include putIfAbsent and remove, where remove will only happen if key mapped to value

Question 21

State some considerations for choosing implementations

Answer 21

Expected size of data 
Efficiency of operations
Optional Operations
Sorting, iterating
Thread safety
Nulls

Question 22

What is an abstract class?

Answer 22

A class that provides some of the code that can be common to multiple implementations of an interface

Question 23

Describe the steps for implementing a new collection

Answer 23

1. Extend appropriate abstract class

2. Provide standard constructors