How would I go about implementing this Java interface?

Question

I am currently in the design mode for this problem:

Implement the Speaker interface that is predefined. Create three classes that implement Speaker in various ways. Create a driver class whose main method instantiates some of these objects and tests their abilities.

How would I go about designing this program and them moving into the coding stage. I want to use these three classes to implement the Speaker interface class: Politician, Lecturer, and Pastor class. The methods I want to use are:

public void speak(); public void announce (String str);

Now for my design and coding, how would I go about to declare and object reference variable and have that variable have multiple references?

Have you gone through the tutorials on how to use interfaces? It will all be explained there. We're not too good at re-writing these tutorials and are much better equipped at helping you with errors once you've made an attempt -- something I strongly urge you to do. — Hovercraft Full Of Eels, Nov 25 '12 at 02:07
(Hint: Conceive of implementing an interface as being similar to subclassing a parent class.) — Hot Licks, Nov 25 '12 at 02:07
How about declaring an object reference variable? Any sample code for an example? — brennaboo, Nov 25 '12 at 02:10

score 1 · Answer 1 · answered Nov 25 '12 at 02:10

1

It's simple really. In brief:

class ClassA implements Speaker
{
   public void speak(){
          System.out.println("I love Java") ; //implement the speak method
    }
}
class ClassB implements Speaker //follow the example of ClassA
class ClassC implements Speaker //same as above

Speaker[] speakers = new Speakers{new ClassA(),new ClassB(),new ClassC()} ;

for(Speaker speaker: speakers)
   speaker.speak(); //polymorphically call the speak() method defined in the contract.

answered Nov 25 '12 at 02:10

Lews Therin

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So for my 3 speaker classes, how would I have each be more specific but still use the speak() and announce() methods. – brennaboo Nov 25 '12 at 02:12
When your speaker class implements an interface, they have to provide an implementation. In the example of ClassA I am saying ClassA will speak by printing out "I love Java".. – Lews Therin Nov 25 '12 at 02:13
Also if you notice the way I'm creating an array of Speakers, not an array of ClassA/B/C. – Lews Therin Nov 25 '12 at 02:15

score 0 · Accepted Answer · answered Nov 25 '12 at 02:11

See "What is an Interface?" http://docs.oracle.com/javase/tutorial/java/concepts/interface.html This will hopefully get you started with the basics you're looking for.

The start of the implementation would look something like the following...

class Politician implements Speaker
{
  public void speak()
  { 
    // Method implementation
  }
  public void announce (String str)
  {
    // Method implementation
  }
}
class Lecturer implements Speaker
{
  public void speak()
  { 
    // Method implementation
  }
  public void announce (String str)
  {
    // Method implementation
  }
}
class Lecturer implements Speaker
{
  public void speak()
  { 
    // Method implementation
  }
  public void announce (String str)
  {
    // Method implementation
  }
}

public static void main(String [] args)
{
   Speaker s1 = new Politician();
   Speaker s2 = new Pastor();
   Speaker s3 = new Lecturer();
   // Do something...
}

score -1 · Answer 3 · answered Nov 25 '12 at 04:05

Use a Factory Method Design Pattern.. Check this article at http://en.wikipedia.org/wiki/Factory_method_pattern

Your code could look something like this, if you use the Factory pattern

public class SpeakerFactory {

      enum SpeakerEnum { POLITICIAN, LECTURER, PASTOR} ;
      Speaker getSpeaker(SpeakerEnum speakerType) {
          switch (speakerType) {

          case POLITICIAN : return new Politician();

          ....

          }
      }

}

How would I go about implementing this Java interface?

3 Answers3