使用Scanner從文件double值讀取 - InputMismatchException？

Question

我嘗試從文件double值中讀取數據，並使用Scanner來達到此目的。

它拋出InputMismatchException：

"input.txt" java.util.InputMismatchException 
    at java.util.Scanner.throwFor(Scanner.java:909) 
    at java.util.Scanner.next(Scanner.java:1530) 
    at java.util.Scanner.nextDouble(Scanner.java:2456) 

而且我不明白爲什麼出現這種情況？

代碼：

public class Largest 
{ 
    public static void main(String[] args) 
    throws FileNotFoundException 
    { 
     String filename = "input.txt"; 
     Scanner in = new Scanner(filename); 

     double largest = in.nextDouble(); 
     while (in.hasNextDouble()) 
     { 
      double input = in.nextDouble(); 
      if (input > largest) 
      { 
       largest = input; 
      } 
     } 
     in.close(); 
     System.out.println("Largest value: " + largest); 
    } 
} 

UPDATE：
我試圖改變double largest = in.nextDouble();到double largest = 0;
但得到錯誤的輸入：

filename  Actual    Expected 
------------------------------------------------------------- 
"input.txt" Largest value: 0.0 Largest value: 1.343239923E9 
"input2.txt" Largest value: 0.0 Largest value: 40.1 

文件內容是這樣的：

89343455 
46746846 
56.78 
55486411 

如何解決這個問題？

Answer 1

我找到了解決方案 - 無需創建文件的對象，然後將其輸送到掃描器類：

String filename = "input.txt"; 
File newFile = new File(filename); 
Scanner in = new Scanner(newFile); 

Answer 2

• 初始化最大到第一雙

• 使用正確的分隔符解析您的輸入（\n =新行）

  String filename = "input.txt"; 
  Scanner in = new Scanner(filename).useDelimiter("\\n"); 
  
  double largest; 
  if (in.hasNextDouble()) 
      largest = in.nextDouble(); 
  
  while (in.hasNextDouble()) 
  { 
      double input = in.nextDouble(); 
      if (input > largest) 
      { 
       largest = input; 
      } 
  } 
  

Answer 3

（覈對型號後）

試試這個

import java.io.File; 
import java.io.FileNotFoundException; 
import java.util.Scanner; 

public class MainClass{ 
public static void main(String[] args) 
     throws FileNotFoundException 
{ 
    Scanner in = new Scanner(new File("D:\\input.txt")); 
    String largestNum=in.next().trim(); 
    double largest = Double.parseDouble(largestNum); 
    while (in.hasNextDouble()) 
    { 
     String Num=in.next().trim(); 
     double input = Double.parseDouble(Num); 
     if (input > largest) 
     { 
      largest = input; 
     } 
    } 
    in.close(); 
    System.out.println("Largest value: " + largest); 
} }