In an attempt to remove duplicate elements from list, I go to the lengths to take advantage of  methods in the java api. After investiagting the document of java api, the result is so satisfying that I speak hightly of wisdom of developer of java language.Next I will introduce charming usage about set in the java. 

 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.TreeSet;

 public class SetUtil
 {

     public static List<String> testStrList = Arrays.asList("Apple", "Orange",
             "Pair", "Grape", "Banana", "Apple", "Orange");

     /**
      * Gets sorted sets which contains no duplicate elements
      *
      * @time Jul 17, 2014 7:58:16 PM
      * @return void
      */
     public static void sort()
     {
         Set<String> sortSet = new TreeSet<String>(testStrList);
         System.out.println(sortSet);
       // output : [Apple, Banana, Grape, Orange, Pair]
     }

     public static void removeDuplicate()
     {
         Set<String> uniqueSet = new HashSet<String>(testStrList);
         System.out.println(uniqueSet);
        <span style="font-family: Arial, Helvetica, sans-serif;">// output : </span><span style="font-family: Arial, Helvetica, sans-serif;">[Pair, Apple, Banana, Orange, Grape]</span>
     }

     public static void reverse()
     {
         Set<String> sortSet = new TreeSet<String>(testStrList);
         List<String> sortList = new ArrayList<String>(sortSet);
         Collections.reverse(sortList);
         System.out.println(sortList);
         // output : [Pair, Orange, Grape, Banana, Apple]
     }

     public static void swap()
     {
         Set<String> sortSet = new TreeSet<String>(testStrList);
         List<String> sortList = new ArrayList<String>(sortSet);
         Collections.swap(sortList, 0, sortList.size() - 1);
         System.out.println(sortList);
         output : [Apple, Orange, Grape, Banana, Pair]
     }

     public static void main(String[] args)
     {
         SetUtil.sort();
         SetUtil.reverse();
         SetUtil.swap();
         SetUtil.removeDuplicate();
     }
 }