21. Collections

Question 1

Although there are different kinds of collections, what particular convenience do they all have in common? (Collections API)

Answer 1

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Question 2

Name four methods from the Collection interface? Which collections have these methods?

Answer 2

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Question 3

What deficiency arguable exists in the use of interfaces as a means of contractual obligation?

Answer 3

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Question 4

What features characterize a collection as being a list?

Answer 4

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Question 5

What is the type parameter of a List used for?

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Question 6

What order does Lists: List interface: iterator() present the elements in?

Answer 6

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Question 7

If we have ArrayList al = new ArrayList(); what type is the object referenced by the variable al - is it ArrayList, List, Collection or Object?

Answer 7

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Question 8

How is Lists: ArrayList collection implemented?

Answer 8

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Question 9

For which implementation of Lists will add(index) and remove(index) instance methods be slow, and for which will they be fast?

Answer 9

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Question 10

How is LinkedList collection implemented?

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Question 11

What features characterize a collection as being a map?

Answer 11

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Question 12

What are the type parameters of a Map interface used for?

Answer 12

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Question 13

How is the TreeMap collection implemented?

Answer 13

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Question 14

Howis the HashMap collection implemented?

Answer 14

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Question 15

What features characterize a collection as being a set?

Answer 15

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Question 16

What is the type parameter of a Set interface used for?

Answer 16

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Question 17

What order does the Sets: Set interface: iterator() present the elements in?

Answer 17

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Question 18

If we have HashSet hs = new HashSet(); what type is the object referenced by the variable hs - is it HashSet, Set, Collection or Object?

Answer 18

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Question 19

How is the TreeSet collection implemented?

Answer 19

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Question 20

What order does Sets: TreeSet: iterator() present the elements in?

Answer 20

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Question 21

How is HashSet collection implemented?

Answer 21

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Question 22

Name a generic class method that is provided in Collections class. What restrictions are placed on its List method argument?

Answer 22

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Question 23

What two abstract methods does this have?

Answer 23

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Question 24

What two stages are involved in this?

Answer 24

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Question 25

What is data stored in at run time? What kinds of things might we want to do with such stored data?

Answer 25

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Question 26

What is the consequence of clashes, and how is their occurrence minimized?

Answer 26

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Question 27

Why is the data structure called OBT?

Answer 27

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Question 28

For what circumstances is linked list better than using an array?

Answer 28

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Question 29

What three instance methods does Integer have in order for it to behave properly in the collections classes?

Answer 29

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Question 30

What is hashCode() used for, and what properties should it have?

Answer 30

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Question 31

What properties must hashCode() have, and what property should it have? How can we achieve this?

Answer 31

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Question 32

When should we use a for-each loop with collections?

Answer 32

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