public abstract class OperacaoMatematica {
  public abstract double calcular(double x, double y);
}

public class Soma extends OperacaoMatematica {
  public double calcular(double x, double y) {
    return x + y;
  }
}

public class Subtracao extends OperacaoMatematica {
  public double calcular(double x, double y) {
    return x - y;
  }
}

A função calcular implementa um exemplo do conceito de