// Product角色，所有实例所共有的公共接口
abstract class Operation {
  public int numA;
  public int numB;
  public abstract int GetResult();
}

// ConcreteProduct 角色，实现 Product 中的接口
class Add extends Operation {
  @Override
  public int GetResult() {
    return numA + numB;
  }
}
//ConcreteProduct 角色，实现 Product 中的接口
class Sub extends Operation {
  @Override
  public int GetResult() {
    return numA - numB;
  }
}
//ConcreteProduct 角色，实现 Product 中的接口
class Mul extends Operation {
  @Override
  public int GetResult() {
    return numA * numB;
  }
}
//ConcreteProduct 角色，实现 Product 中的接口
class Div extends Operation {
  @Override
  public int GetResult() {
    if (numB == 0) {
      System.out.println("ERROR!");
      return -1;
    }
    return numA / numB;
  }
}

// 工厂角色，简单工厂模式的核心，它负责实现创建所有实例的内部逻辑
class OperationFactory {
  public static Operation CreateOperation (char operate) {
    Operation oper = null;
    switch(operate) {
    case '+':
      oper = new Add();
      break;
    case '-':
      oper = new Sub();
      break;
    case '*':
      oper = new Mul();
      break;
    case '/':
      oper = new Div();
      break;
    default:
      break;
    }
    return oper;
  }
}

public class SimpleFactoryPattern {
  public static void main(String[] args) {
    int numA = 10;
    int numB = 3;
    int result = 0;
    Operation oper = OperationFactory.CreateOperation('+');
    oper.numA = numA;
    oper.numB = numB;
    result = oper.GetResult();
    System.out.println(numA + " + " + numB + " = " + result);
  }
}

10 + 3 = 13