计算器小程序（无界面）

(下面有女朋友写的简单版的计算器，小白适用)

先上源码

package zxt.Reflection;

import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class calc {
    public static void main(String[] args) {
        System.out.println("欢迎使用计算器！请输入式子，以回车结束。");
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();
        double n1, n2;
        String a1="";
        String a2="";
        String f = null;
        List list = Arrays.asList(str.split(""));
        for (String s : list) {
            if (s.equals("+") || s.equals("-") || s.equals("*") || s.equals("/")) {
                f = s;
            } else if (f == null) {
                a1 += s;
            }else{
                a2 += s;
            }
        }
        n1 = Double.parseDouble(a1);
        n2 = Double.parseDouble(a2);
        iCalc ca;
        switch (f) {
            case "+":
                ca = (double b1, double b2) -> { System.out.println(b1 + b2);};
                ca.lambda(n1, n2);
                break;
            case "-":
                ca = (double b1, double b2) -> { System.out.println(b1 - b2);};
                ca.lambda(n1, n2);
                break;
            case "*":
                ca = (double b1, double b2) -> { System.out.println(b1 * b2);};
                ca.lambda(n1, n2);
                break;
            case "/":
                ca = (double b1, double b2) -> { System.out.println(b1 / b2);};
                ca.lambda(n1, n2);
                break;
            default:
                System.out.println("你输入的式子不正确！");
        }
    }
}
@FunctionalInterface
interface iCalc {
    void lambda(double a, double b);
}

示例：

List list = Arrays.asList(str.split(""));

将式子转成列表(这是个不可增删改查的列表，用于遍历)。

for (String s : list) {
            if (s.equals("+") || s.equals("-") || s.equals("*") || s.equals("/")) {
                f = s;
            } else if (f == null) {
                a1 += s;
            }else{
                a2 += s;
            }
        }

增强for循环遍历，变量f记录符号位，也作为标志位，检测是前一个数字还是后一个数字。

@FunctionalInterface
interface iCalc {
    void lambda(double a, double b);
}

函数式接口,用于实现lambda表达式。

ca = (double b1, double b2) -> { System.out.println(b1 + b2);};
ca.lambda(n1, n2);

switch里四次实现的lambda表达式并调用。

(这个需要依次输入)

import java.util.Scanner;

public class Task_Calculator {
   public static void main(String[] args) {
       double result = 0;
       System.out.println("请输入第一个数");
       Scanner scanner = new Scanner(System.in);
       double x = scanner.nextDouble();
       System.out.println("请输入符号");
       String fh = scanner.next();
       System.out.println("请输入第二个数");
       double y = scanner.nextDouble();

       switch (fh) {
           case "+":
               result = x + y;
               break;
           case "-":
               result = x - y;
               break;
           case "*":
               result = x * y;
               break;
           case "/":
               if (y == 0) {
                   System.out.println("除数不能为0！");
                   break;
               } else {
                   result = x / y;
                   break;
               }
           default:
               System.out.println("请输入正确的+-*/符号");
       }
       System.out.println("运算结果为"+result);
   }
}