COP 3530
Section U02
Fall 2012


                                A Generic Point Program
                                =======================


I. The class Point.java 

// example of a generic class

public class Point <T>
{
    // the fields
    private T xCoord;
    private T yCoord;
    
    // the constructor
    public Point(T x, T y)
    {
        xCoord = x;
        yCoord = y;
    }        
    
    // the set methods
    public void setX(T x)
    { 
        xCoord = x;
    }
    
    public void setY(T y)
    { 
        xCoord = y;
    }
    
    // the get methods
    public T getX()
    {
        return xCoord;
    }        
    
    public T getY()
    {
        return yCoord;
    }        
}    
    
    

II. A driver


// a driver for the Point class
public class Generics1 
{

    public static void main(String[] args)
    {
        // print the title
        System.out.println("Testing the Generic Point Class");
        System.out.println("===============================\n\n");

        // form a point with real coordinates
        System.out.println("We form a point with coordinates 3.5 and 2.3 . ");
        Point<Double> p1 = new Point<Double>(3.5,2.3);
        printPoint(p1);

        // form a point with String coordinates
        System.out.println("\nWe form a point with coordinates \"Poco\" and \"Pelo\" .");
        Point<String> p2 = new Point<String>("Poco", "Pelo");
        printPoint(p2);
        System.out.println("We change the x-coordinate to \"Muy Poco\" .");
        p2.setX("Muy Poco");
        System.out.println("The x-coordinate is " + p2.getX());

        // form a point with integer coordinates but set T= Double
        System.out.println("\nWe form a point with coordinates 3 and 2. ");
        Integer a = new Integer(3);
        Integer b = new Integer(2);
        Point<Integer> p3 = new Point<>(a,b); 
        int x = p3.getX();
        System.out.println("The x-coordinate is " + x);
        
        // form a point with real coordinates but set T= Integer
        System.out.println("We form a point with coordinates 3.5 and 2.3 . ");
        Point<Integer> p4 = new Point<>(3.5,2.3); // syntax error
        printPoint(p4);

    }

    // the printPoint method
    public static void printPoint(Point<?> point)
    {
        System.out.println("The x-coordinate is " + point.getX());
        System.out.println("The y-coordinate is " + point.getY());
    }
}



III. The output:


run:
Testing the Generic Point Class
===============================


We form a point with coordinates 3.5 and 2.3 . 
The x-coordinate is 3.5
The y-coordinate is 2.3

We form a point with coordinates "Poco" and "Pelo" .
The x-coordinate is Poco
The y-coordinate is Pelo
We change the x-coordinate to "Muy Poco" .
The x-coordinate is Muy Poco

Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - The type of <T>Point(T,T) is erroneous
	at generics1.Generics1.main(Generics1.java:42)
We form a point with coordinates 3 and 2. 
The x-coordinate is 3
We form a point with coordinates 3.5 and 2.3 . 
Java Result: 1
BUILD SUCCESSFUL (total time: 1 second)