Lying design pattern ------ simple factory pattern

Factory Method pattern: a factory method pattern defines an interface for creating an object, but let subclasses decide which class to instantiate technology. The method of making a factory to instantiate the class to delay its subclasses.

A simple factory pattern:

Examples of objects are no longer used when the new Object () form, related classes can be instantiated according to the user's choice. For the client, to rely on a specific class of addition. Specific examples described are given only to the plant, the plant will automatically return to a specific instance of an object.

 

 

import lombok.Data;

@Data
public abstract class Operation {

    private double numberA = 0;
    private double numberB = 0;

    public abstract double getResult() throws Exception;
}

public class OperationAdd extends Operation{
    @Override
    public double getResult() {
        return getNumberA() + getNumberB();
    }
}

public class OperationSub extends Operation {
    @Override
    public double getResult() {
        return getNumberA() - getNumberB();
    }
}

public class OperationMul extends Operation {
    @Override
    public double getResult() {
        return getNumberA() * getNumberB();
    }
}

public class OperationDiv extends Operation  {
    @Override
    public double getResult() throws Exception {
        if(getNumberB() == 0){
            throw new Exception("除数不能为0");
        }
        return getNumberA() / getNumberB();
    }
}

public class OperationFactory {

    public static Operation createOperation(String operate){
        Operation operation = null;
        switch (operate){
            case "+" :
                operation = new OperationAdd();
                break;
            case "-" :
                operation = new OperationSub();
                break;
            case "*" :
                operation = new OperationMul();
                break;
            case "/" :
                operation = new OperationDiv();
                break;
        }
        return operation;
    }
}

public class TestOperation {

    public static void main(String[] args) {
        Operation operation = OperationFactory.createOperation("+");
        try {
            operation.setNumberA(10);
            operation.setNumberB(20);
            System.out.println(operation.getResult());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}