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import org.junit.Test;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class TestCalc {

@Test

public void testCalculator() {

String input = "1+1";//输入

String rule = "(\\d+\\.?\\d*)([+\\-*/])(\\d+\\.?\\d*)";

Matcher matcher = Pattern.compile(rule).matcher(input);

double result;

if (!matcher.find()) throw new NullPointerException();

double num1 = Double.parseDouble(matcher.group(1));

double num2 = Double.parseDouble(matcher.group(3));

switch (matcher.group(2)) {

case "+":

result = num1 + num2;

break;

case "-":

result = num1 - num2;

break;

case "*":

result = num1 * num2;

break;

case "/":

result = num1 / num2;

break;

default:

result = Double.NaN;

}

System.out.printf("%.2f", result);

}

}