java.util(一)，TreeSet

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import java.util.*;public class TestTreeSet {  public static void main(String[] args) {    // Create a hash set    Set<String> set = new HashSet<String>();    // Add strings to the set    set.add("London");    set.add("Paris");    set.add("New York");    set.add("San Francisco");    set.add("Beijing");    set.add("New York");    TreeSet<String> treeSet = new TreeSet<String>(set);    System.out.println("Sorted tree set: " + treeSet);    // Use the methods in SortedSet interface    System.out.println("first(): " + treeSet.first());    System.out.println("last(): " + treeSet.last());    System.out.println("headSet(): " + treeSet.headSet("New York"));    System.out.println("tailSet(): " + treeSet.tailSet("New York"));    // Use the methods in NavigableSet interface    System.out.println("lower(\"P\"): " + treeSet.lower("P"));    System.out.println("higher(\"P\"): " + treeSet.higher("P"));    System.out.println("floor(\"P\"): " + treeSet.floor("P"));    System.out.println("ceiling(\"P\"): " + treeSet.ceiling("P"));    System.out.println("pollFirst(): " + treeSet.pollFirst());    System.out.println("pollLast(): " + treeSet.pollLast());    System.out.println("New tree set: " + treeSet);  }}