工厂方法模式：工厂方法模式定义一个用于创建对象的接口，让子类决定实例化哪一个类。工厂方法使一个类的实例化延迟到其子类。

一、简单工厂模式：

实例化对象的时候不再使用 new Object()形式，可以根据用户的选择条件来实例化相关的类。对于客户端来说，去除了具体的类的依赖。只需要给出具体实例的描述给工厂，工厂就会自动返回具体的实例对象。

 

 

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();
        }
    }
}