Android™ How to Program, Second Edition

J.8. Sets

A Set is an unordered Collection of unique elements (i.e., no duplicate elements). The collections framework contains several Set implementations, including HashSet and TreeSet. HashSet stores its elements in a hash table, and TreeSet stores its elements in a tree. Hash tables are presented in Section J.9.

Figure J.8 uses a HashSet to remove duplicate strings from a List. Recall that both List and Collection are generic types, so line 16 creates a List that contains String objects, and line 20 passes a Collection of Strings to method printNonDuplicates.

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 1   // Fig. J.8: SetTest.java 2   // HashSet used to remove duplicate values from an array of strings. 3   import java.util.List; 4   import java.util.Arrays; ...