CollectionExampleGenerics.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

class CollectionExample {
  // Lets start collection...
  // Non-generic
  List list = new ArrayList();
  Set set = new HashSet();
  Map map  = new HashMap();
  
  public void mapExample () {
        // there must be a unique key
       map.put (21, "Mango");    // key-value 
       map.put (22, "Mango"); 
       map.put (22, "Orange");
       map.put (23, "Orange");
    }
    
    public void listExample () {
        // duplicates are allowed
       list.add ("Mango"); 
       list.add ("Mango"); 
       list.add ("Orange");
       list.add ("Orange");
       list.add (23);
       list.add (23.87);
    }
    
    public void setExample () {
        // no duplicates
       set.add ("Mango");
       set.add ("Mango");
       set.add ("Orange");
       set.add ("Orange");
       set.add (23);
    }
    
    // Generics
    // declare generics for below mentioned data structures.
    public void genericListExample () {
       names.add ("Mango"); 
       names.add ("Mango"); 
       names.add ("Orange");
       names.add ("Orange");
    }
    
    public void genericMapExample () {
        uniqueListOfUsernames.put (1, "vslala");
        uniqueListOfUsernames.put (2, "vs_lala");
        uniqueListOfUsernames.put (3, "pikachu");
        uniqueListOfUsernames.put (3, "pvrano"); // same key
    }
    
    public void genericSetExample () {
        price.add(12.00d);
        price.add(22.00d);
        price.add(32.00d);
        price.add(42.00d);
        price.add(52.00d);
    }
    
    public void printList(Object obj) {
        System.out.println("Loop will run " + (list.size()) + " times");
        if (obj instanceof List) {
            List list = (List) obj; // type casted to List
            for (int i = 0; i < list.size(); i++) {
                System.out.println(list.get(i));
            }
        }

        if (obj instanceof Set) {
            Set set = (Set) obj;
            Iterator itr = set.iterator();
            while (itr.hasNext()) {
                System.out.println (itr.next());
            }
        }
        
        if (obj instanceof Map) {
            Map map = (Map) obj;
            Iterator itr = map.entrySet().iterator();
            while (itr.hasNext()) {
                Map.Entry item = (Map.Entry) itr.next();
                System.out.println(item.getKey() + ": " + item.getValue());
            }
        }
    }
    
    public static void main (String [] args) {
      CollectionExample c = new CollectionExample();
//        c.listExample();
//        c.setExample();
//        c.mapExample();
//            c.printList(c.list);

//        c.genericListExample();
//        c.genericMapExample();
            c.genericSetExample();
          
//        c.printGenericList();
            c.printGenericSet();
//          c.printGenericMap();
    }
}