Java Interface, Abstract Class and Concrete Class

AbstractMathOperation.java

public abstract class AbstractMathOperation implements MathOperation{
  public void preOperate(Integer... values){
    System.out.println("This is a pre operation ");
  }
  public void postOperate(Integer... values){
    System.out.println("This is a post operation ");
  }
  
  public Integer operate(Integer... values){
    preOperate(values);
    Integer result = doOperation(values);
    postOperate(values);
    return result;
  }
  /**
   * This method should be implemented by all the sub classes to implement actual logic "middle code"
   */
  public abstract Integer doOperation(Integer... values);
}
  

Add.java

public class Add extends AbstractMathOperation{
  @Override
  public Integer doOperation(Integer... values){
    Integer i = 0;
    for(Integer value : values){
      i += value;
    }
    return i;
  }
}
  

Main.java

public class Main{
  public static final MathOperation ADD = new Add();
  public static final MathOperation SUBTRACT = new Subtract();
  public static final MathOperation MULTIPLY = new Multiply();
  
  public static final void main(String [] args){
    System.out.ptintln(ADD.operate(1,2,3,4,5,6));
    System.out.ptintln(SUBTRACT.operate(10,5,2));
    System.out.ptintln(MULTIPLY.operate(1,2,3,4,5,6));
  }
}

MathOperation.java

public interface MathOperation{
   public Integer operate(Integer ... values);
}

Multiply.java

public class Multiply extends AbstractMathOperation{
  @Override
  public Integer doOperation(Integer... values){
    Integer i = 1;
    for(Integer value : values){
      i *= value;
    }
    return i;
  }
}

Subtract

public class Subtract extends AbstractMathOperation{
  @Override
  public Integer doOperation(Integer... values){
    Integer i = 0;
    for(Integer value : values){
      i -= value;
    }
    return i;
  }
}