COP 3530
Section U02
Spring 2015


                              The ArrayList Class: Raw and Generic
                              ====================================



I. The Program:

// an example of generics
import java.util.ArrayList;

public class Generics3 
{

    // we use array lists
    public static void main(String[] args) 
    {

        System.out.println("Array Lists: Raw Type and Generic");
        System.out.println("=================================\n\n");
        
        System.out.println("We use an untyped array list.");
        System.out.println("In it we put an integer, a string, and a real number.");
        
        ArrayList junk = new ArrayList();
        junk.add(10);
        junk.add("Papa Bill");
        junk.add(3.5);
        
        System.out.println("We try to retrieve the item at index 0 as an integer.");
        int i = (Integer) junk.get(0);
        System.out.println("It is " + i);
        
        System.out.println("We try to retrieve the item at index 1 as a decimal.");
        try
        {
            double x = (Double) junk.get(0);
        }    
        catch( ClassCastException e)
        {
            System.out.println("We get " + e);
        }    
        
        // Now let us use generics
        System.out.println("\nNow let us use generics.");
        System.out.println("We form an array list of strings and put the names "
            + "\nPapa Bill, Grandpa Smith, Poco Pelo.");
        ArrayList<String> names = new ArrayList<>();
        names.add("Papa Bill");
        names.add("Grandpa Smith");
        names.add("Poco Pelo");
        
        System.out.println("The name as index 1 is " + names.get(1) + ".");
    }
    
}


II. The Output:

run:
Array Lists: Raw Type and Generic
=================================


We use an untyped array list.
In it we put an integer, a string, and a real number.
We try to retrieve the item at index 0 as an integer.
It is 10
We try to retrieve the item at index 1 as a decimal.
We get java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Double

Now let us use generics.
We form an array list of strings and put the names 
Papa Bill, Grandpa Smith, Poco Pelo.
The name as index 1 is Grandpa Smith
BUILD SUCCESSFUL (total time: 0 seconds)