简单工厂模式

以实现加、减、乘、除的计算器功能为例

初级代码：

输入数字交互界面

@SuppressWarnings("resource")
    public static void main(String[] args) {

        System.out.println("**********************************************");
        System.out.println("《大话设计模式》代码样例");
        System.out.println();

        try {
            Scanner sc = new Scanner(System.in);

            System.out.println("请输入数字A：");
            double numberA = Double.parseDouble(sc.nextLine());
            System.out.println("请选择运算符号(+、-、*、/)：");
            String strOperate = sc.nextLine();
            System.out.println("请输入数字B：");
            double numberB = Double.parseDouble(sc.nextLine());

            double result = getResult(numberA, numberB, strOperate);

            System.out.println("结果是：" + result);
        } catch (Exception e) {
            System.out.println("您的输入有错：" + e.toString());
        }

        System.out.println();
        System.out.println("**********************************************");

    }

运算方法：

public static double getResult(double numberA, double numberB, String operate) {
        double result = 0d;
        switch (operate) {
            case "+":
                result = numberA + numberB;
                break;
            case "-":
                result = numberA - numberB;
                break;
            case "*":
                result = numberA * numberB;
                break;
            case "/":
                result = numberA / numberB;
                break;
            case "pow":
                result = java.lang.Math.pow(numberA, numberB);
                break;
        }
        return result;
    }

缺陷：无法做到灵活的可修改和扩展

比如说加个其他运算，导致需要重新修改运算方法且需要把加减乘除的代码重新编译一遍；且如果不小心改了其他方法，程序会出现问题，给程序带来了风险；

好的代码应该是，修改其中一个不影响另外的几个，增加运算算法也不影响其它代码；

高级写法：

思路：

到底要实例化谁，将来会不会增加实例化的对象，也就是说会不会增加运算符，这是很容易变化的地方，应该考虑用一个单独的类来做这个创造实例的过程，这就是工厂

classDiagram class Operation{ <<abstract>> +double numberA +double numberB +double getResult() } class OperationAdd{ +double getResult() } class OperationSub{ +double getResult() } class OperationFactory { +Operation createOperation(String operator) } class interactionView { main(String[] args) } interactionView o-- OperationFactory : createOperation OperationFactory o-- Operation Operation <|-- OperationAdd Operation <|-- OperationSub

输入数字交互界面：

public static void main(String[] args){

        System.out.println("**********************************************");       
        System.out.println("《大话设计模式》代码样例");
        System.out.println();       

        try {
            Scanner sc = new Scanner(System.in);

            System.out.println("请输入数字A：");  
            double numberA = Double.parseDouble(sc.nextLine());
            System.out.println("请选择运算符号(+、-、*、/)：");    
            String strOperate = sc.nextLine();
            System.out.println("请输入数字B：");  
            double numberB = Double.parseDouble(sc.nextLine());

            Operation oper = OperationFactory.createOperate(strOperate);

            double result = oper.getResult(numberA,numberB);

            System.out.println("结果是："+result);  
        }
        catch(Exception e){
            System.out.println("您的输入有错："+e.toString()); 
        }

        System.out.println();
        System.out.println("**********************************************");

    }

工厂类

public class OperationFactory {

    public static Operation createOperate(String 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;
        }
        return oper;
    }

}

抽象化运算类

public abstract class Operation {

    public double getResult(double numberA, double numberB){
        return 0d;
    }

}

加

public class Add extends Operation {

    public double getResult(double numberA, double numberB){
        return numberA + numberB;
    }

}

526互联

大话设计模式之简单工厂模式笔记