Java Scanner 不会读取整个文件 [重复]答案

【问题标题】：Java Scanner won't read through the whole file [duplicate]Java Scanner 不会读取整个文件 [重复]
【发布时间】：2016-03-13 08:47:37
【问题描述】：

所以我试图通读整个文件并打印它的内容，它确实如此。但是当我用新的扫描仪再次检查它以打印带有一些部分名称的内容时，它只会检查一些文件。

这是我的代码：

import java.util.*;
import java.io.*;


public class FileReader {
   public static void main(String[] args) throws FileNotFoundException {
      Scanner read = new Scanner(new File("sample.txt")); 

      while(read.hasNextLine()) {
         System.out.println(read.nextLine());
      } 
      System.out.println();   

      Scanner read2 = new Scanner(new File("sample.txt")); 
      int numQuestions = read2.nextInt();
      System.out.println("Numbers of questions: " + numQuestions);
      System.out.println();

      while(read2.hasNextLine()) {
         int points, numChoices;
         String question, answer;

         if(read2.next().equals("TF")) {
            points = read2.nextInt();
            System.out.println("Points for TF: " + points); 
            read2.nextLine();  // must be done because it does not consume the \n character
            question = read2.nextLine();
            System.out.println("Question for TF: " + question);    
            answer = read2.next();
            System.out.println("Answer for TF: " + answer);
         }
         else if(read2.next().equals("SA")) {
            points = read2.nextInt();
            System.out.println("Points for SA: " + points);
            read2.nextLine();  // must be done because it does not consume the \n character
            question = read2.nextLine();            
            System.out.println("Question for SA: " + question); 
            answer = read2.next();
            System.out.println("Answer for SA: " + answer);
         }
         else if(read2.next().equals("MC")) {
            points = read2.nextInt();
            System.out.println("Points for MC: " + points);
            read2.nextLine();  // must be done because it does not consume the \n character
            question = read2.nextLine();
            System.out.println("Question for MC: " + question);
            read2.nextLine();
            numChoices = read2.nextInt();
            for(int i = 0; i < numChoices; i++) {
               System.out.println(read2.nextLine());
            }
            answer = read2.next();
            System.out.println("Answer for MC: " + answer); 
         }
      }
   }
}

这是我正在读取的文件：

3 
TF 5
There exist birds that can not fly. (true/false) 
true 
MC 10 
Who was the president of the USA in 1991? 
6 
Richard Nixon 
Gerald Ford 
Jimmy Carter 
Ronald Reagan 
George Bush Sr. 
Bill Clinton 
E 
SA 20 
What city hosted the 2004 Summer Olympics? 
Athens

这是我得到的输出：

3 
TF 5
There exist birds that can not fly. (true/false) 
true 
MC 10 
Who was the president of the USA in 1991? 
6 
Richard Nixon 
Gerald Ford 
Jimmy Carter 
Ronald Reagan 
George Bush Sr. 
Bill Clinton 
E 
SA 20 
What city hosted the 2004 Summer Olympics? 
Athens

Numbers of questions: 3

Points for TF: 5
Question for TF: There exist birds that can not fly. (true/false) 
Answer for TF: true

如您所见，第一个Scanner 读取整个文件并打印出来。但是当我第二次尝试使用部分名称时，它只通过问题 1 的部分。

【问题讨论】：

您只使用一次Scanner read，然后创建第二个Scanner read2 类型的对象。如果您不再需要read，您应该使用相同的变量来创建新的扫描器对象：read=new Scanner(new File("sample.txt"));。在这种情况下，变量更少，代码更易于阅读。

标签： java file java.util.scanner

【解决方案1】：

我认为这是因为您通过 else-if 语句扫描了 3 次，所以您应该创建一个变量 String type = read2.next(); 并在 if-else 中使用它。

【讨论】：

【解决方案2】：

如您所知，read2.next() 读取下一个单词。当您多次调用它时，它会读取多个单词。

所以当你这样做时

 // read a word, and if it's not TF, discard it.
 if(read2.next().equals("TF")) {

 // read another word, and it it's not SA discard it.
 else if(read2.next().equals("SA")) {

您的意图是读一次单词并多次比较。一个简单的方法是使用开关。

// read once,
switch(read.next()) {
    case "TF":
         // do something
         break;

    case "SA":
         // do something
         break;

    // more case(s)
}

【讨论】：