Generic Collections - Java: How to Program Early Objects - page 712

5 import java.util.HashSet;

6 import java.util.Set;

7 import java.util.Collection;

8
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public class SetTest

10

{

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public static void main(String[] args)

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{

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// create and display a List<String>

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String[] colors = { "red" , "white" , "blue" , "green" , "gray" ,

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"orange" , "tan" , "white" , "cyan" , "peach" , "gray" , "orange" };

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List<String> list = Arrays.asList(colors);

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System.out.printf( "List: %s%n" , list);

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// eliminate duplicates then print the unique values

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printNonDuplicates(list);

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}

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// create a Set from a Collection to eliminate duplicates

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private static void printNonDuplicates( Collection<String> values )

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{

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// create a HashSet

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Set<String> set = new HashSet<>(values);

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System.out.printf( "%nNonduplicates are: " );

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31

for (String value : set)

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System.out.printf( "%s " , value);

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System.out.println();

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}

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} // end class SetTest

List: [red, white, blue, green, gray, orange, tan, white, cyan, peach, gray,
orange]

Nonduplicates are: orange green white peach gray cyan red blue tan

Fig. 16.16 | HashSet used to remove duplicate values from an array of strings. (Part 2 of 2.)

Sorted Sets
The collections framework also includes the SortedSet interface (which extends Set ) for
sets that maintain their elements in sorted order—either the elements' natural order (e.g.,
numbers are in ascending order) or an order specified by a Comparator . Class TreeSet im-
plements SortedSet . The program in Fig. 16.17 places String s into a TreeSet . The
String s are sorted as they're added to the TreeSet . This example also demonstrates range-
view methods, which enable a program to view a portion of a collection.
Line 14 creates a TreeSet<String> that contains the elements of array colors , then
assigns the new TreeSet<String> to SortedSet<String> variable tree . Line 17 outputs
the initial set of strings using method printSet (lines 33-39), which we discuss momen-
tarily. Line 31 calls TreeSet method headSet to get a subset of the TreeSet in which every