25. Networking

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Review Questions

Sections 22.1 “22.2

22.1	Describe the Java Collections Framework. List the interfaces, convenience abstract classes, and concrete classes.
22.2	Can a collection object be cloned and serialized?
22.3	The hashCode method and the equals method are defined in the Object class. Why are they redefined in the Collection interface?
22.4	Find the default implementation for the equals method and the hashCode method in the Object class from the source code of Object.java.

Section 22.3 Sets

22.5	How do you create an instance of Set ? How do you insert a new element in a set? How do you remove an element from a set? How do you find the size of a set?
22.6	What are the differences between HashSet , LinkedHashSet , and TreeSet ?
22.7	How do you traverse the elements in a set? Can you traverse the elements in a set in an arbitrary order?
22.8	How do you sort the elements in a set using the compareTo method in the Comparable interface? How do you sort the elements in a set using the Comparator interface? What would happen if you added an element that cannot be compared with the existing elements in a tree set? [Page 740]
22.9	Suppose that set1 is a set that contains the strings "red" , "yellow" , "green" , and that set2 is another set that contains the strings "red" , "yellow" , "blue" . Answer the following questions: What are set1 and set2 after executing set1.addAll(set2) ? What are set1 and set2 after executing set1.add(set2) ? What are set1 and set2 after executing set1.removeAll(set2) ? What are set1 and set2 after executing set1.remove(set2) ? What are set1 and set2 after executing set1.retainAll(set2) ? What is set1 after executing set1.clear() ?

Section 22.4 The Comparator Interface

22.10	What are the differences between the Comparable interface and the Comparator interface? Which package is Comparable in, and which package is Comparator in?
22.11	The Comparator interface contains the equals method. Why is the method not implemented in the GeometricObjectComparator class in this section?

Section 22.5 Lists

22.12	How do you add and remove elements from a list? How do you traverse a list in both directions?
22.13	Suppose that list1 is a list that contains the strings "red" , "yellow" , "green" , and that list2 is another list that contains the strings "red" , "yellow" , "blue" . Answer the following questions: What are list1 and list2 after executing list1.addAll(list2) ? What are list1 and list2 after executing list1.add(list2) ? What are list1 and list2 after executing list1.removeAll(list2) ? What are list1 and list2 after executing list1.remove(list2) ? What are list1 and list2 after executing list1.retainAll(list2) ? What is list1 after executing list1.clear() ?
22.14	What are the differences between ArrayList and LinkedList ? Are all the methods in ArrayList also in LinkedList ? What methods are in LinkedList but not in ArrayList ?
22.15	How do you create a set or a list from an array of objects?

Section 22.6 Static Methods for Lists and Collections

22.16	Are all the methods in the Collections class static?
22.17	Which of the following static methods in the Collections class are for lists, and which are for collections? sort, binarySearch, reverse, shuffle, max, min, disjoint , frequency
22.18	Show the printout of the following code: import java.util.*; public class Test { public static void main(String[] args) { List<String> list = Arrays.asList( "yellow" , "red" , "green" , "blue" ); Collections.reverse(list); System.out.println(list); [Page 741] List<String> list1 = Arrays.asList( "yellow" , "red" , "green" , "blue" ); List<String> list2 = Arrays.asList( "white" , "black" ); Collections.copy(list1, list2); System.out.println(list1); Collection<String> collection1 = Arrays.asList( "red" , "cyan" ); Collection<String> collection2 = Arrays.asList( "red" , "blue" ); Collection<String> collection3 = Arrays.asList( "pink" , "tan" ); System.out.println(Collections.disjoint(collection1, collection2)); System.out.println(Collections.disjoint(collection1, collection3)); Collection<String> collection = Arrays.asList( "red" , "cyan" , "red" ); System.out.println(Collections.frequency(collection, "red" )); } }
22.19	Which method can you use to sort the elements in an ArrayList or a LinkedList ? Which method can you use to sort an array of strings?
22.20	Which method can you use to perform binary search for elements in an ArrayList or a LinkedList ? Which method can you use to perform binary search for an array of strings?
22.21	Write a statement to find the largest element in an array of comparable objects?

Section 22.7 Vectors and Stacks

22.22	How do you create an instance of Vector ? How do you add or insert a new element into a vector? How do you remove an element from a vector? How do you find the size of a vector?
22.23	How do you create an instance of Stack ? How do you add a new element into a stack? How do you remove an element from a stack? How do you find the size of a stack?
22.24	Does Listing 22.1, TestHashSet.java, compile and run if line 7 ( Set set = new HashSet() ) is replaced by one of the following statements? Collection set = new LinkedHashSet(); Collection set = new TreeSet(); Collection set = new ArrayList(); Collection set = new LinkedList(); Collection set = new Vector(); Collection set = new Stack();

Section 22.8 Queues and Priority Queues

22.25	Is java.util.Queue a subinterface of java.util.Collection , java.util.Set , or java.util.List ? Does LinkedList implement Queue ?
22.26	How do you create a priority queue for integers? By default, how are elements ordered in a priority queue? Is the element with the least value assigned the highest priority in a priority queue?
22.27	How do you create a priority queue that reverses the natural order of the elements?

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Section 22.9 Maps

22.28	How do you create an instance of Map ? How do you add a pair consisting of an element and a key into a map? How do you remove an entry from a map? How do you find the size of a map? How do you traverse entries in a map?
22.29	Describe and compare HashMap , LinkedHashMap , and TreeMap .
22.30	Show the printout of the following code: public class Test { public static void main(String[] args) { Map map = new LinkedHashMap(); map.put( "123" , "John Smith" ); map.put( "111" , "George Smith" ); map.put( "123" , "Steve Yao" ); map.put( "222" , "Steve Yao" ); System.out.println( "(1) " + map); System.out.println( "(2) " + new TreeMap(map)); } }