##Simple Factory Mode##

What is factory mode

**Simple factory mode**: Whoever you want to instance, and whether you want to add instantiated objects in the future, should consider using a separate class to create this instance, which is the factory.

Step One

public class OperationObject {
    private double _numberA = 0;
    private double _numberB = 0;

    public double get_numberA() {
        return _numberA;
    }

    public void set_numberA(double _numberA) {
        this._numberA = _numberA;
    }

    public double get_numberB() {
        return _numberB;
    }

    public void set_numberB(double _numberB) {
        this._numberB = _numberB;
    }
    public double getResult(){
        double result = 0;
        return result;
    }
}

Step 2:

//addition
public class OperationAdd extends OperationObject {
    public double getResult(){
        double result = 0;
        result = get_numberA()+get_numberB();
        return result;
    }
}
//addition
public class OperationDiv extends OperationObject{
    public double getResult() {
        double result = 0;
        if (get_numberB() == 0){
            try {
                throw new Exception("Divisor can not Be zero");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        result = get_numberA() / get_numberB();
        return result;
    }
}
//multiplication
public class OperationMul extends OperationObject {
    public double getResult(){
        double result = 0;
        result = get_numberA() * get_numberB();
        return result;
    }
}
//division
public class OperationSub extends OperationObject {
    public double getResult(){
        double result = 0;
        result = get_numberA() - get_numberB();
        return result;
    }
}

Step Three

//Simple factory mode: Whoever you want to instantiate, and whether you want to add instantiated objects in the future, should consider using a separate class to create this instance. This is the factory.
//In a word, a factory contains a bunch of objects that need instances
public class OperationFactory {
    public static OperationObject createOperation(String operation){
        //Responsible for production addition, subtraction, multiplication and division
        OperationObject operationObject = null;
        switch (operation){
            case "+":
                operationObject = new OperationAdd();
                break;
            case "-":
                operationObject = new OperationSub();
                break;
            case "*":
                operationObject = new OperationMul();
                break;
            case "/":
                operationObject = new OperationDiv();
                break;
        }
        return operationObject;
    }
}

Step 4

public class factoryDesign {
    public static void main(String[] args) {
        //The type of calculation required by the instance
        OperationObject operationObject = OperationFactory.createOperation("-");
        operationObject.set_numberA(2);
        operationObject.set_numberB(4);
        double result = operationObject.getResult();
        System.out.println(result);
    }
}

The above content is personal notes after learning big talk design mode, do not like to spray.