文章目录
问题:
简单写一个计算器,输入2个数和运算符,得到结果。
分析:
这一题看上去很简单,但如果面试时你写的是下面这种代码,那大概率是过不了的。
上面代码也能实现题目的功能,但是代码没有错就是好的吗?
以上代码复用性低;可维护性差,如果要改+的逻辑,就会牵一发而动全身;扩展性差,如果这个时候新增开平方的逻辑怎么办?
以下介绍一个简单的设计模式,大家可以带着上面的问题分析一下以下代码:
简单工厂模式:用一个类来创造实例的过程。
package Chapter1;import java.util.Objects;
import java.util.Scanner;import Chapter1.operation.Operation;public class Calculator {public static void main(String[] args) {Scanner sc = new Scanner(System.in);System.out.println("请输入第一个数:");Double firstNum = sc.nextDouble();System.out.print("请输入运算符:");String operationSymbol = sc.next();System.out.println("请输入第二个数:");Double secondNum = sc.nextDouble();Operation operation = new OperationFactory().createOperation(operationSymbol);while(Objects.isNull(operation)){System.out.println("运算符输入错误,请重新输入");operationSymbol = new Scanner(System.in).next();operation = new OperationFactory().createOperation(operationSymbol);}operation.setFirstNum(firstNum);operation.setSecondNum(secondNum);System.out.print(operation.getResult());}
}
package Chapter1;import Chapter1.operation.*;public class OperationFactory {public Operation createOperation(String operation) {switch (operation) {case "+":return new AddOperation();case "-":return new SubOperation();case "*":return new MutOperation();case "/":return new DivOperation();}return null;}
}
package Chapter1.operation;import lombok.Data;@Data
public class Operation {private Double firstNum;private Double secondNum;private Double result;
}
package Chapter1.operation;import lombok.NonNull;public class AddOperation extends Operation {@Overridepublic Double getResult() {return this.getFirstNum() + this.getSecondNum();}
}
package Chapter1.operation;import lombok.NonNull;public class SubOperation extends Operation {@Overridepublic Double getResult() {return this.getFirstNum() - this.getSecondNum();}
}
package Chapter1.operation;import lombok.NonNull;public class MutOperation extends Operation {@Overridepublic Double getResult() {return this.getFirstNum() * this.getSecondNum();}
}
package Chapter1.operation;import java.util.Scanner;import lombok.NonNull;public class DivOperation extends Operation {@Overridepublic Double getResult() {Double firstNum = this.getFirstNum();Double secondNum = this.getSecondNum();while (secondNum == 0) {System.out.println("被除数不能为0, 请重新输入:");secondNum = new Scanner(System.in).nextDouble();}return firstNum / secondNum;}
}