[deepdave]

I need to convert 'Bounceable' from an abstract class to an interface - and then update concrete class Basketball to implement 'Bounceable' - how do I do this ? thanks

public abstract class Bounceable extends Ball
{
public Bounceable(String type)
{
super(type);
}
public abstract String bounce();
}

(here is Ball)
public abstract class Ball
{
private String type;
public Ball(String type)
{
this.type = type;
}
public String getType()
{
return type;
}
public abstract void play();
}
}

(here is Basketball)
public class Basketball
extends Bounceable
{
public Basketball()
{
super("Basketball");
}
public String bounce()
{
return " dribble...";
}
public void play()
{
System.out.println("Basketball begins with a tipoff");
}
}

[Trollhorn]

First of all, some general thoughts... Bounceable should NOT extends Ball because a Bounceable Object IS NOT in all cases a Ball (IS A is what extends actually mean)...

I would suggest the following:

1. create a Bounceable interface

public interface Bounceable {
    String bounce(); // all method declarations in interfaces are public abstract implicitly
}

2. create an abstract Ball class

public abstract class Ball {
    private String type; 

    protected Ball(String type) {
        this.type = type;
    }

    public getType() {
        return type;
    }

    public abstract void play();
}

3. let Basketball implement Bounceable and extend Ball (so a Basketball IS A ball, which is right AND a bounceable object, which is also true)

public class Basketball extends Ball implements Bounceable {
    public Basketball(String type) {
        super(type);
    }

    @Override
    public String bounce() {
        return " dribble... ";
    }

    @Override 
    public void play() {
        System.out.println("Basketball begins with a tipoff");
    }
}

That should do the trick ;-)! Didn't try out the code but at least it should give you an idea :-)!

[deepdave]

Thanks!
In 'Ball' I get the msg 'The method getType() is undefined for the type Ball'
which I think is causing my problem when I test ...
I omitted that there is a driver class to test with (oops):
public class PolyTest4
{
public static void main(String[] args)
{
Ball[] ball = {new Baseball(),new Basketball(),new Bowlingball(),new Tennisball()};
int i=1; // added to allow for ball #

System.out.println("For each type of ball...\n");

for(Ball b : ball)
{
System.out.println("Ball #"+(i)+" is a "+b.getType());
i++;

System.out.print("Playing: ");
b.play();
// checks to see if it is an object of type Bounceable
if( b instanceof Bounceable)
// if so, call bounce method of Bounceable object
System.out.println("Bouncing "+((Bounceable)b).bounce());
else
System.out.println("You can't bounce this ball!");

System.out.println("\n");
}

System.out.println("\nEnd of program.");
}
}
which returns error messages:
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
The constructor Basketball() is undefined
The constructor Tennisball() is undefined
The method getType() is undefined for the type Ball

at Polytest.PolyTest4.main(PolyTest4.java:14)

(the other 2 classes referred to are below (didn't kinow if I had to change them as they don't extend 'Bounceable)

public class Bowlingball
extends Ball
{
public Bowlingball()
{
super("Bowlingball");

}


public void play()
{
System.out.println("Set up the pins. Do you know how to score?");

}

}
and
public class Baseball
extends Ball
{
public Baseball()
{
super("Baseball");
}


@Override
public void play()
{
System.out.println("The American pasttime - batter up!");
}

}

Thanks again

[Trollhorn]

Ups, I omitted the return type in getType()... maybe I shouldn't post code in the future I haven't tested ;-)... of course it should have been

    public String getType() {
        return type;
    }

That should actually do the trick, ran your Test-PRG with the Ball classes and it worked fine.

One more note: You can retrieve the Classname of a class via the Class object.

Something like this:

    String someString = "abc";
    System.out.println(someString.getClass().getSimpleName());

Bye, Oliver

[deepdave]

Thanks, Again, BTW ... still getting:
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
The constructor Basketball() is undefined
The constructor Tennisball() is undefined

at Polytest.PolyTest.main(PolyTest.java:14)public class PolyTest

[Trollhorn]

Could you please post your Basketball and Tennisball classes? It seems like both classes don't implement a parameterless constructor.

Constructor with one parameter

public Basketball(String type) {
    super(type);
}

Parameterless constructor

public Basketball() {
    super("Basketball");
}

To instantiate an object using the parameterless constructor:

Ball ball = new BasketBall();

To instantiate an object using the constructor with one parameter:

Ball ball = new BasketBall("Basketball");

Greets, Oliver

[deepdave]

Thanks again from this Mainframe Dinosaur ... I am trying to change 'Bounceable' to an Interface and modify the appropriate concrete classes (Basketball and Tennisball and not Bowling ball and Baseball?) to implement the new interface. I just renamed them all with a '4' appended to keep them distinct from the originals ... Again, the single error is when I try to run Polytest4 (The constructor Basketball4() is undefined
The constructor Tennisball4() is undefined
here they are:

package Polytest;

public class PolyTest4
{
public static void main(String[] args)
{
Ball4[] ball4 = {new Baseball4(),new Basketball4(),new Bowlingball4(),new Tennisball4()};
int i=1; // added to allow for ball #

System.out.println("For each type of ball...\n");

for(Ball4 b : ball4)
{
System.out.println("Ball #"+(i)+" is a "+b.getType());
i++;

System.out.print("Playing: ");
b.play();
// checks to see if it is an object of type Bounceable4
if( b instanceof Bounceable4)
// if so, call bounce method of Bounceable4 object
System.out.println("Bouncing "+((Bounceable4)b).bounce());
else
System.out.println("You can't bounce this ball!");

System.out.println("\n");
}

System.out.println("\nEnd of program.");
}
}
/////////////////////////////////////////////////////////////////
package Polytest;

public abstract class Ball4
{
private String type;

protected Ball4(String type)
{
this.type = type;
}

public String getType()
{
return type;
}

public abstract void play();
}
//////////////////////////////////////////////////////////
package Polytest;
public interface Bounceable4
{
String bounce(); // all method declarations in interfaces are public abstract implicitly
}
///////////////////////////////////////////////////////////
package Polytest;

public class Bowlingball4
extends Ball4
{
public Bowlingball4()
{
super("Bowlingball4");

}


public void play()
{
System.out.println("Set up the pins. Do you know how to score?");

}

}
///////////////////////////////////////
package Polytest;

public class Baseball4
extends Ball4
{
public Baseball4()
{
super("Baseball4");
}


@Override
public void play()
{
System.out.println("The American pasttime - batter up!");
}
}
////////////////////////////////////
package Polytest;

public class Basketball4 extends Ball4 implements Bounceable4
{
public Basketball4(String type)
{
super(type);
}

@Override
public String bounce()
{
return " dribble... ";
}

@Override
public void play()
{
System.out.println("Basketball begins with a tipoff");
}
}
////////////////////////
package Polytest;

public class Tennisball4 extends Ball4 implements Bounceable4
{
public Tennisball4(String type)
{
super(type);
}

@Override
public String bounce()
{
return " dribble... ";
}

@Override
public void play()
{
System.out.println("Basketball begins with a tipoff");
}
}
//////////////////////////////

[Trollhorn]

Thanks, now I got the problem...

There a two ways to solve your problem:

You can

1. change the code in PolyTest4 to:

public class PolyTest4
{
public static void main(String[] args)
{
Ball4[] ball4 = {new Baseball4(),new Basketball4("Basketball"),new Bowlingball4(),new Tennisball4("Tennisball")};
int i=1; // added to allow for ball #

System.out.println("For each type of ball...\n");

for(Ball4 b : ball4)
{
System.out.println("Ball #"+(i)+" is a "+b.getType());
i++;

System.out.print("Playing: ");
b.play();
// checks to see if it is an object of type Bounceable4
if( b instanceof Bounceable4)
// if so, call bounce method of Bounceable4 object
System.out.println("Bouncing "+((Bounceable4)b).bounce());
else
System.out.println("You can't bounce this ball!");

System.out.println("\n");
}

System.out.println("\nEnd of program.");
}
}

or

2. you can change the constructor signatures (the signature basically is the constructor name + number of parameters + their types) in the Basketball and Tennisball classes to:

public class Basketball4 extends Ball4 implements Bounceable4
{
public Basketball4()
{
super("Basketball");
}

@Override
public String bounce()
{
return " dribble... ";
}

@Override
public void play()
{
System.out.println("Basketball begins with a tipoff");
}
}

public class Tennisball4 extends Ball4 implements Bounceable4
{
public Tennisball4()
{
super("Tennisball");
}

@Override
public String bounce()
{
return " dribble... ";
}

@Override
public void play()
{
System.out.println("Basketball begins with a tipoff");
}
}

If you have further questions regarding Objects and Classes, refer to:

Lesson: Classes and Objects (The Java™ Tutorials > Learning the Java Language)

or simply ask :-)!

Bye, Oliver