5. HashSets and Sets

import java.util.HashSet;
import java.util.Set;
import java.util.TreeSet;
 
public class App {
 
    public static void main(String[] args) {
 
        // HashSet does not retain order.
        // Set<String> set1 = new HashSet<String>();
 
        // LinkedHashSet remembers the order you added items in
        // Set<String> set1 = new LinkedHashSet<String>();
 
        // TreeSet sorts in natural order
        Set<String> set1 = new TreeSet<String>();
 
        if (set1.isEmpty()) {
            System.out.println("Set is empty at start");
        }
 
        set1.add("dog");
        set1.add("cat");
        set1.add("mouse");
        set1.add("snake");
        set1.add("bear");
 
        if (set1.isEmpty()) {
            System.out.println("Set is empty after adding (no!)");
        }
 
        // Adding duplicate items does nothing.
        set1.add("mouse");
 
        System.out.println(set1);
 
        // ///////// Iteration ////////////////
 
        for (String element : set1) {
            System.out.println(element);
        }
 
        // ////////// Does set contains a given item? //////////
        if (set1.contains("aardvark")) {
            System.out.println("Contains aardvark");
        }
 
        if (set1.contains("cat")) {
            System.out.println("Contains cat");
        }
 
        /// set2 contains some common elements with set1, and some new
 
        Set<String> set2 = new TreeSet<String>();
 
        set2.add("dog");
        set2.add("cat");
        set2.add("giraffe");
        set2.add("monkey");
        set2.add("ant");
         
        ////////////// Intersection ///////////////////
         
        Set<String> intersection = new HashSet<String>(set1);
         
        intersection.retainAll(set2);
         
        System.out.println(intersection);
         
        ////////////// Difference /////////////////////////
         
        Set<String> difference = new HashSet<String>(set2);
         
        difference.removeAll(set1);
        System.out.println(difference);
    }
 
}