4.1 Java4010r review  (Page 3/3)

Answers

Answer 25

False. Listing 1 causes the following text to appear on the screen:

1234

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Answer 24

True.

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Answer 23

True.

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Answer 22

True.

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Answer 21

False. The concept of in order means different things for different Collection objects. For a collection instantiated from the TreeSet class, for example, in order means in ascending order. However, that may not be the case for a differentobject instantiated from a class that implements the Collection interface.

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Answer 20

True.

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Answer 19

True.

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Answer 18

False. In Listing 1 , when the fillIt method returns, the TreeSet object contains four (not five) elements with no duplicates. Each element is a reference to an object of type Integer . Those references are maintained in such a way as to make them accessible in ascending order, based on the int values encapsulated in each of the Integer objects.

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Answer 17

False. In Listing 1 , when the fillIt method returns, the TreeSet object contains four (not five) elements with no duplicates.

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Answer 16

True. For example, the behavior of the add method for an object of the TreeSet class will probably be different from the behavior ofthe add method for an object of some other class that implements the Collection interface.

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Answer 15

False. The fillIt method receives the reference as type Collection . This method doesn't know, and doesn't care, what the actual type of the object is. All it cares about is that the object is a Collection object. (Otherwise, the object's reference couldn't be passed in as a parameter. A type mismatch would occur.) A TreeSet object is a Collection because the TreeSet class implements the Collection interface. A Button object is not a Collection because the Button class does not implement the Collection interface.

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Answer 14

True.

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Answer 13

True.

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Answer 12

True.

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Answer 11

False. The TreeSet class implements the SortedSet interface. This guarantees that the contents of a TreeSet object will be in ascending element order, regardless of the order in which the elements areadded.

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Answer 10

False. An object of the TreeSet class also is a Set . One of the characteristics of a Java Set (an object that implements the Set interface) is that it can contain no duplicate elements. Therefore, a TreeSet object can contain no duplicate elements.

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Answer 9

True.

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Answer 8

True.

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Answer 7

False. a TreeSet object is a Collection . Therefore, a reference to a TreeSet object can be stored in a reference variable of type Collection , and can be treated as the generic type Collection .

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Answer 6

True.

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Answer 5

False. Listing 1 instantiates an object of the TreeSet class and stores the object's reference in a reference variable of type Collection named ref .

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Answer 4

True.

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Answer 3

False. Some collections are ordered and others are not.

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Answer 2

True.

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Answer 1

False. The framework is designed to encourage you to reuse rather than to reinvent collections and maps.

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Miscellaneous

This section contains a variety of miscellaneous information.

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