/*
 *  TGn03:  Before Autoboxing/Unboxing.  Collection objects, such as
 *  ArrayList, can only hold objects.  The base types (int, char, double,
 *  etc.) are not part of the Java object hierarchy.  In order to store
 *  them into an ArrayList, we need to 'hide' them within objects.  Java
 *  provides a set of "wrapper" classes for this purpose.  For example,
 *  the class Double is the wrapper class for double values.
 *  This example shows what needs to be done to store doubles into an
 *  ArrayList in versions of Java prior to 1.5.
 *
 *  If you compile this example with a 1.5 (5.0) or later version of Java,
 *  you will get a warning from the compiler that "unchecked or unsafe
 *  operations" are being used.  This illustrates the need for generics:
 *  Without them, the compiler was unable to help the programmer recognize
 *  code that was potentially mixing object references in useless ways.
 *  Now Java can recognize such situations and provide feedback.
 */

import java.io.*;
import java.util.*;

public class TGn03
{
    public static void main (String [] args) 
    {
        ArrayList myList;
        Double dblObj1, dblObj2;
        double temp1, temp2;

        myList = new ArrayList();

        temp1 = 72.8;
        dblObj1 = new Double(temp1);       // wrap the double value
        myList.add(dblObj1);               // wrapped double can be added

        dblObj2 = (Double) myList.get(0);  // retrieve object reference & cast
        temp2 = dblObj2.doubleValue();     // extract value from wrapper

        System.out.println(temp2);
    }
}