java - 读取输入文件到链表的节点错误

Question

我想做的是打印链表节点中的数据(变量系数和度)。

但是当我读取 input.txt 文件中的一行时出现问题。input.txt 文件的内容如下

2
2 0
3 0
2
-2 0
3 4

但是我的代码无法读取此内容，打印一条错误消息，例如java.lang.NumberFormatException:对于输入字符串:“01”

<小时/>

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;

public class Assignment21 {
    public static void main(String[] args) {
    try {
        LinkedList polynomialN = new LinkedList();
        LinkedList polynomialM = new LinkedList();

        BufferedReader in = new BufferedReader(new FileReader("input.txt"));
        String firstEntryNum;
        firstEntryNum = in.readLine();
        int entryNum = Integer.valueOf(firstEntryNum); 

        for(int i = 0; i < entryNum; i++){ 
            String temp = in.readLine(); 

            int divider = temp.indexOf(" ");
            int coefficient = Integer.parseInt(temp.substring(0, divider));
            int degree = Integer.parseInt(temp.substring(divider) + 1); //지수 입력받기

            polynomialN.add(new Node(coefficient, degree));
        }

        String secondEntryNum;
        secondEntryNum = in.readLine();
        entryNum = Integer.valueOf(secondEntryNum);

        for(int i = 0; i < entryNum; i++){
            String temp = in.readLine();

            int divider = temp.indexOf(" "); 
            int coefficient = Integer.parseInt(temp.substring(0, divider)); //계수 입력받기
            int degree = Integer.parseInt(temp.substring(divider) + 1); //지수 입력받기

            polynomialM.add(new Node(coefficient, degree));
        }

        polynomialN.print();
        polynomialM.print();

        in.close();

        BufferedWriter out = new BufferedWriter(new FileWriter("output.txt"));
        out.close();
    } catch (Exception e) {
        System.err.println(e);
        System.exit(1);
        // TODO: handle exception
    }
}
}

class Node{
int coefficient;
int degree;
Node nextNode;

public Node(int coefficient, int degree) {
    this.coefficient = coefficient;
    this.degree = degree;
}
}

class LinkedList {
private Node head;

public void add(Node newNode){
    if (head == null)
        head = newNode;
    else {
        Node tail = head;
        while(tail.nextNode != null){
            tail = tail.nextNode;
        }   
        tail.nextNode = newNode;
    }
}

public void print() {
    StringBuffer sb = new StringBuffer();
    Node current = head;
    int size = 0;

    while (current != null){
        sb.append(current.coefficient);
        sb.append(" ");
        sb.append(current.degree);
        current = current.nextNode;
        size++;
    }

    System.out.println("[" + sb + "]");
    System.out.println("size: " + size);
}
}

提前致谢

Answer 1

java.lang.NumberFormatException: 基本上意味着您尝试解析为 int 的输入实际上并不是 int。另外，我会使用 Scanner API 来读取输入，这更简单并且需要更少的代码。

Scanner sc = new Scanner(System.in);
int firstLine = Integer.parseInt(sc.nextLine());

如果你想要一个字符串，你可以使用

String firstLine = sc.nextLine();

现在继续使用获取输入，

while(sc.hasNextLine()){
   String something = sc.nextLine();
}

此外，在使用子字符串将一行字符串解析为整数除法器、系数和度数的部分中，这可以更容易地完成。

String[] arr = something.split(" ");

现在您可以使用

int divider = Integer.parseInt(arr[0])
int coefficient = Integer.parseInt(arr[1])
int degree = Integer.parseInt(arr[2])