Java拆分不能使它适用于负数

Question

我的教授让我们做一个简单的加法和减法计算器，但是输入必须是像"5-5“、"60+70”或"-8+10“这样的整个表达式。

Scanner console = new Scanner(System.in);

int sum;

String expression = console.nextLine();
String[] split = expression.split("(?<=\\d)(?=\\D)|(?<=\\D)(?=\\d)");

int a = Integer.parseInt(split[0]);
int b = Integer.parseInt(split[2]);

String operator = split[1];

switch (operator) {

    case "+":
        sum = a + b;
        System.out.println(sum);
        break;

    case "-":
        sum = a - b;
        System.out.println(sum);
        break;
}

这是我的代码，它适用于前两个示例，但不适用于最后一个示例，其中第一个整数是负数，例如"-8+10"，不，我不能用任何其他方法。我必须在单个字符串中输入整个表达式。

Answer 1

您可以用(?<=\\d)(?=\\D)替换正则表达式。这是寻找出现(非数字)(数字)对。

关于你的例子：

5-5 => "5“和"-5”

60+70 => "60“和"+70”

-8+10 => "-8“和"+10”

    int sum;
    Scanner console = new Scanner(System.in);

    String expression = console.nextLine();
    String[] split = expression.split("(?<=\\d)(?=\\D)"); //split by signed numers

    int a = Integer.parseInt(split[0]); //First numer at index 0
    int b = Integer.parseInt(split[1]); //Second numer at index 1

    sum = a + b; //You don't need operator. Instead just add a and b
    System.out.println(sum);

你可以摆脱operator。注意，如果a或b为负值，则仍然可以添加它们以获得正确的结果。

Answer 2

您可以通过始终以0开头并将每个“部件”作为数字或运算符来修复此问题。此解决方案还允许任意长度，因此您不仅限于两个数字。

import java.util.*;
import java.util.stream.*;

public class Main {
  public static void main(String[] args) {
    System.out.println(new Expression("-8+12").evaluate());
  }
}

class Expression {

  public List<Part> parts;

  public Expression(String expression) {
    String[] split = expression.split("(?<=\\d)(?=\\D)|(?<=\\D)(?=\\d)");
    this.parts = Stream.of(split).map(Part::new).collect(Collectors.toList());

  }

  public Double evaluate() {
    double total = 0;
    Operator currentOperator = new Operator("+");
    
    for (Part currentPart : parts) {
      if (currentPart.isNumber()) {
        total = currentOperator.apply(total, currentPart.getNumberValue());
      } else {
        currentOperator = new Operator(currentPart.value);
      }
    }
    
    return total;
  }

}

class Part {

  public String value;

  public Part(String value) {
    this.value = value;
  }

  public double getNumberValue() {
    return Double.parseDouble(this.value);
  }

  public boolean isNumber() {
    try {
      double number = Double.parseDouble(this.value);
      return true;
    } catch (Exception e) {
      return false;
    }
  }
}

class Operator {
  public String value;

  public Operator(String value) {
    this.value = value;
  }

  public double apply(double first, double second) {
    switch(this.value) {
      case "+":
        return first + second;
      case "-":
        return first - second;
      default:
        throw new RuntimeException("Not a valid operator");
    }
  }
}

你可以在这里玩这个解决方案。