请问我哪里出了问题？ - java help on CodeGym

package zh.codegym.task.task13.task1326;

/*
对文件中的偶数进行排序
*/

import java.io.*;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;

public class Solution {
    public static void main(String[] args) throws IOException {
        //在此编写你的代码
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        ArrayList<Integer> list = new ArrayList<>();

        //读取文件名
        FileInputStream fis = new FileInputStream(reader.readLine());

        int read;
        String s;
        //如果输入为空则结束循环
        while (!(s = reader.readLine()).equals("")) {
            try{
                //将输入行存入列表
                read = Integer.parseInt(s);
                list.add(read);
            }catch (NumberFormatException e){
                //捕获异常并跳过该行进入下一行
            }
        }

        ArrayList<Integer> list2 = new ArrayList<>();

        //将所有偶数存入新列表
        for (int i = 0; i < list.size(); i++) {
            if ((list.get(i)%2) == 0) {
                list2.add(list.get(i));
            }
        }
        //排序
        Collections.sort(list2);

        //遍历输出
        for (int n : list2) {
            System.out.println(n);
        }

        fis.close();
        reader.close();
    }
}

public class Solution { public static void main(String[] args) throws IOException { //在此编写你的代码 BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); //读取文件名 File fileName = new File(reader.readLine()); reader.close(); FileInputStream fis = new FileInputStream(fileName); //创建读取文件内容的BufferedReader对象 BufferedReader readerFile = new BufferedReader(new InputStreamReader(fis)); ArrayList<Integer> list = new ArrayList<>(); //读取文件内容 int read; String s; try{ //如果读取到文档结尾则结束循环 while (!(s = readerFile.readLine()).equals("")) { try{ //将读取行内容转换为Integer read = Integer.parseInt(s); //如果是偶数，则添加到列表 if (read%2 == 0) { list.add(read); } }catch (NumberFormatException e){ //捕获不能转换为Integerd的异常，跳过该行进入下一行 } } }catch (NullPointerException e) { //捕获空指针异常并跳过，进入下一个操作 } fis.close(); readerFile.close(); //排序 Collections.sort(list); //遍历输出 for (int n : list) { System.out.println(n); } } }

受欢迎
新
旧

你必须先登录才能发表评论

Guadalupe Gagnon

级别 37 ，Tampa，United States

5 五月 2021, 17:11

解决方法

#1 The 'reader' object in this code is for keyboard input. The task wants you to read from a file. Line 25 is using 'reader' which means it is reading keyboard input. #2 When a BufferedReader reaches the end of a file, each subsequent reads will return null. Line 25 checks for empty input [.equals("")]. This will result in a null pointer exception after the last line is read from the file. This isn't wrong, but if you would like to improve your code I would suggest that you take the logic at line 39 of testing for even numbers and move it to original reading loop, right between lines 28 and 29. You don't need a second list if you just check the number before putting it in list one. In that way you can just remove 35-42 completely.

Ghiosux

级别 17 ，Chengdu，China

6 五月 2021, 05:16

Thank you so much! I made it！ Here is my improved code：