List lst = new LinkedList();   // use "LinkedList" implementation
// or
List lst = new Vector();       // use "Vector" implementation
// or
List lst = new Stack();        // use "Stack" implementation

// lst is designed to hold Strings
lst.add(new Integer(88));  // adds an Integer, implicitly upcast to Object, okay in compile/runtime
 
Iterator iter = lst.iterator();
while (iter.hasNext()) {
   String str = (String)iter.next(); // compile okay but runtime ClassCastException
   System.out.println(str);
}

List<String> lst = new ArrayList<String>();  // read as List of Strings, ArrayList of Strings

// Post-JDK 1.5 with Generics
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;
 
public class ArrayListPostJDK15Test {
   public static void main(String[] args) {
      List<String> lst = new ArrayList<String>();  // Inform compiler about the type
      lst.add("alpha");         // compiler checks if argument's type is String
      lst.add("beta");
      lst.add("charlie");
      System.out.println(lst);  // [alpha, beta, charlie]
 
      Iterator<String> iter = lst.iterator();   // Iterator of Strings
      while (iter.hasNext()) {
         String str = iter.next();  // compiler inserts downcast operator
         System.out.println(str);
      }
 
//      lst.add(new Integer(1234));   // ERROR: compiler can detect wrong type
//      Integer intObj = lst.get(0);  // ERROR: compiler can detect wrong type
 
      // Enhanced for-loop (JDK 1.5)
      for (String str : lst) {
         System.out.println(str);
      }
   }
}

// Pre-JDK 1.5
List lst = new ArrayList();  // No type information
lst.add("alpha");   // Without generics, compiler can't check if the type is correct

// Pre-JDK 1.5
Integer intObj = new Integer(5566);    // wrap int to Integer
int i = intObj.intValue();             // unwrap Integer to int
 
Double doubleObj = new Double(55.66);  // wrap double to Double
double d = doubleObj.doubleValue();    // unwrap Double to double

// JDK 1.5
Integer intObj = 5566;    // autobox from int to Integer
int i = intObj;           // auto-unbox from Integer to int
 
Double doubleObj = 55.66; // autoboxing from double to Double
double d = doubleObj;     // atuo-unbox from Double to double

// Pre-JDK 1.5
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;
 
public class PrimitiveCollectionPreJDK15 {
   public static void main(String[] args) {
      List lst = new ArrayList();
 
      // Add 10 random primitive int into the List
      Random random = new Random();
      for (int i = 1; i <= 10; ++i) {
         // Wrap the primitive int into Integer, upcast to Object
         lst.add(new Integer(random.nextInt(10)));
      }
      System.out.println(lst);
 
      Iterator iter = lst.iterator();
      while (iter.hasNext()) {
         // Explicit downcast to Integer, then unwrap to int
         int i = ((Integer)iter.next()).intValue();   // un-safe at runtime
         System.out.println(i);
      }
   }
}

// Post-JDK 1.5
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;
 
public class PrimitiveCollectionJDK15 {
   public static void main(String[] args) {
      List<Integer> lst = new ArrayList<Integer>();
 
      // Add 10 random primitive int into the List
      Random random = new Random();
      for (int i = 1; i <= 10; ++i) {
         lst.add(random.nextInt(10)); // autobox to Integer, upcast to Object, type-safe
      }
      System.out.println(lst);
 
      // Transverse via iterator
      Iterator<Integer> iter = lst.iterator();
      while (iter.hasNext()) {
         int i = iter.next();  // downcast to Integer, auto-unbox to int, type-safe
         System.out.println(i);
      }
 
      // Transverse via enhance for-loop
      for (int i : lst) {      // downcast to Integer, auto-unbox to int, type-safe
         System.out.println(i);
      }
 
      // Retrieve via for-loop with List's index
      for (int i = 0; i < lst.size(); ++i) {
         int j = lst.get(i);   // downcast to Integer, auto-unbox to int, type-safe
         System.out.println(j);
      }
   }
}