java - java中带分隔符的2个或多个数字

Question

我有这个基本程序，在输入个位数时效果很好。但是当计算一个包含多个数字的表达式时，比如 1337 - 456 + 32，程序不会继续......它就像我什么也没做一样。它不会卡住或输出错误消息，它只是停止。

代码如下:

import java.io.*;
import java.util.*;
public class Tester {
    public static void main(String args[]) {
        Scanner kb = new Scanner(System.in);
        System.out.print("Enter number: ");
        String s = kb.nextLine();
        Scanner sc = new Scanner(s);
        //Set delimiters to a plus sign surrounded by any amount of white space...or...
        // a minus sign surrounded by any amount of white space.
        sc.useDelimiter("\\s*");
        int sum = 0;
        int temp = 0;
        int intbefore = 0;
        
        if (sc.hasNext("\\-")) {
            sc.next();
            if (sc.hasNextInt()) {
                intbefore = sc.nextInt();
                int temper = intbefore * 2;
                intbefore = intbefore - temper; 
            }
        }
        if (sc.hasNextInt()) {
            intbefore = sc.nextInt(); //now its at the sign (intbefore = 5)
        }
        sum = intbefore;
        
        while (sc.hasNext()) {
            if(sc.hasNext("\\+")) { //does it have a plus sign?
                sc.next(); //if yes, move on (now at the number)
                System.out.println("got to the next();");
                
                if(sc.hasNextInt()) { //if there's a number
                    temp = sc.nextInt();
                    sum = sum + temp; //add it by the sum (0) and the sum of (5) and (4)
                    System.out.println("added " + sum);
                }
            }
            if(sc.hasNext("\\-")) {
                sc.next();
                System.out.println("got to the next();");
                
                if (sc.hasNextInt()) {
                    temp = sc.nextInt();
                    sum = sum - temp; //intbefore - temp == 11
                    System.out.println("intbefore: " + intbefore + "  temp: " + temp);
                    System.out.println("subtracted " + sum); // subtracted by 11
                }
            }
        }
        System.out.println("Sum is: " + sum);
    }
}

帮助解释为什么会发生这种情况以及如何解决它？(如果有帮助，我正在使用 netbeans)

此外，我假设输入的每个数字之间都有一个空格，例如:123 + -23 - 5

Answer 1

我尝试执行您的代码，这就是我的发现。

假设您的输入是 12+1。

Not sc.hasNextInt() 会给你 1 你要分配给 intbefore。

接下来，您代码中的 while 循环将进入无限循环，因为 sc.hasNext() 将始终为真(并在这种情况下返回 2)，但它不会' 匹配 while 循环中的两个 if 条件，从而使您的代码在无限循环中运行。现在继续努力。一切顺利。