Computer Science 15-110, Fall 2009
Class Notes:  The JCF, Part 1:  Lists, Sets, and Maps

1. Getting Started with the JCF
2. Code from Class
   1. ArrayList Demo
   2. File + HashSet Demo
   3. HashSet + HashMap Demo

1. Review these notes:  Getting Started with the JCF
    
2. Code from Class
    
   1. ArrayList Demo
      We used ArrayLists in the text adventure we wrote in class.
       
   2. File + HashSet Demo
      Using File and HashSet to list the files that were added/deleted between two directories.

      import java.util.*;
      import java.io.*;
      
      class FileAndSetDemo {
        
        public static HashSet<String> diff(HashSet<String> set1,
                                           HashSet<String> set2) {
          HashSet<String> diff = new HashSet<String>();
          for (String s : set1)
            if (!set2.contains(s))
              diff.add(s);
          return diff;
        }
        
        public static HashSet<String> getDir(String dirName) {
          File dir = new File(dirName);
          HashSet<String> set = new HashSet<String>();    
          String[] files = dir.list();
          for (String file : files)
            set.add(file);
          return set;
        }
        
        public static void main(String[] args) {
          HashSet<String> fileSet1 = getDir("dir1");
          HashSet<String> fileSet2 = getDir("dir2");
          
          System.out.println("Files in dir1 but not in dir2:");    
          System.out.println(diff(fileSet1, fileSet2));
      
          System.out.println("Files in dir2 but not in dir1:");    
          System.out.println(diff(fileSet2, fileSet1));
        }
      }

   3. HashSet and HashMap Demo
      Using a HashSet to test for set membership and a HashMap to count the number of times different strings were entered by the user.

      import java.util.*;
      
      class SetsAndMapsDemo {
        
        public static void main(String[] args) {    
          Scanner scanner = new Scanner(System.in);
      
          System.out.println("******************************");
          System.out.println("Set Demo");    
          System.out.println("******************************");
          HashSet<String> set = new HashSet<String>();
          while (true) {
            System.out.print("Enter a string (or 'q' to quit Set demo / start Map demo): ");
            String s = scanner.next();
            if (s.equals("q")) break;
            System.out.println("  set.contains(" + s + ") = " + set.contains(s));
            set.add(s);
          }
      
          System.out.println();
          System.out.println("******************************");
          System.out.println("Map Demo");    
          System.out.println("******************************");
          HashMap<String,Integer> map = new HashMap<String,Integer>();    
          while (true) {
            System.out.print("Enter a string (or 'q' to quit): ");
            String s = scanner.next();
            if (s.equals("q")) break;
            
            // Integer iInt = map.get(s);
            // int i = ((iInt == null) ? 0 : iInt);
            
            int i = ((map.keySet().contains(s)) ? map.get(s) : 0);
      
            System.out.println("  You entered '" + s + "' " + (i+1) + " time(s).");
            map.put(s, i+1);
          }
        }
      }

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