How to use getters of different strategies in strategy pattern

In the code example that i have below, i am accessing each property of the class through getters in main(), however I do not think this is a good design because the interfaceA which is returned will have no idea about these getters even though programmatically it is right.

And to have a common function that returns both, each of them return different type. Is it a good idea to have the getters as a function in the interface itself? in that case i would need to implement in all the classes that i implement.

Please help me with this design on how to access properties of classes that are different from each other implementing the same interface.

public interface interfaceA {
  method();
}

public classA implements interfaceA {
   int a;

int b;

   public method() { }

  public getA() {
    return a;
  }

public getB() {
    return b;
  }
}

public classB implements interfaceA {
  array arr;

   public method() { }

  public getArray() {
    return arr;
  }
}

public commonClass {

 public getClass() {
  if (condition) return new classA();
 else 
   return new classB();

 } 
}

public void main() {
  classDefinition = (new commonClass()).getClass();

if(condition)
  var a = classDefinition.getA();
  var b = classDefinition.getB();
else
  var array = classDefinition.getArray();
}