大话设计模式-简单工厂模式

 Java版实现代码：

/***
 * 这个类是所有运算类的父类 拥有运算的基本属性
 */
public class Operation {
    private double numberA;
    private double numberB;

    public double getNumberA() {
        return numberA;
    }

    public void setNumberA(double numberA) {
        this.numberA = numberA;
    }

    public double getNumberB() {
        return numberB;
    }

    public void setNumberB(double numberB) {
        this.numberB = numberB;
    }

    /**
     * @return 计算的结果
     * @throws Exception 运算时的异常
     */
    public double GetResult() throws Exception {
        double result = 0;
        return result;
    }
}

/**
 * 加法类
 */
public class OperationAdd extends Operation {
    @Override
    public double GetResult() {
        return getNumberA() + getNumberB();
    }
}

/**
 * 减法类
 */
public class OperationSub extends Operation {
    @Override
    public double GetResult() {
        return getNumberA()-getNumberB();
    }
}

/**
 * 乘法类
 */
public class OperationMul extends Operation {
    @Override
    public double GetResult() {
        return getNumberA()*getNumberB();
    }
}

/***
 * 除法类
 */
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();
    }
}

/**
 * 简单工厂类 含有一个静态方法
 * 用于根据运算符返回具体的运算实例
 */
public class OperationFactory {
    public static Operation createOperate(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 Main {
    public static void main(String[] args) throws Exception {
        Operation operation = OperationFactory.createOperate("+");
        operation.setNumberA(1);
        operation.setNumberB(2);
//        这里其实是由Operation具体的子类实现的具体功能
        double result = operation.GetResult();
        System.out.println(result);
    }
}