Java Scanner无法读取

Question

我试图从一个文件中读取,该文件的格式为:someName:aDoubleNumber,并返回名称和double.我写过以下扫描仪,但它不起作用,任何想法为什么？

Scanner readFile = new Scanner("text.txt");
readFile.useDelimiter(":");
while (fileScanner.hasNext()) {
String name = readFile.next();
}

Answer 1

你不是在读文件.你正在读字符串"text.txt".你需要一个文件.

    Scanner readFile = new Scanner(new File("text.txt")); // don't forget to catch FileNotFoundException!
    readFile.useDelimiter(":|\\n");
    while (fileScanner.hasNext()) {
       String name = readFile.next();
       double value = readFile.nextDouble();
       System.out.println(name + " " + value);
    }

我从您的评论中获取了代码并进行了格式化,我得到了这个

public class MyProject { 
    class FileInput { 
        Scanner readFile = new Scanner(new File("text.txt")); // don't forget to catch FileNotFoundException! 
        readFile.useDelimiter(":|\\n"); 
        while (fileScanner.hasNext()) { 
            String name = readFile.next(); 
            double value = readFile.nextDouble(); 
            System.out.println(name + " " + value); 
        } 
    }
}

现在你似乎遇到了问题 - 也许你的意思class FileInput是public void fileInput() throws Exception？当我这样做时,它会编译.现在我们需要一个main()方法来运行它!所以我补充一下:

public static void main(String[] args) throws Exception {
    MyProject proj = new MyProject();
    proj.fileInput();
}

现在,当我运行它时,我实际上遇到了错误.这意味着我给你开始的代码实际上存在问题.当然,该代码从未打算复制/粘贴,但更多的是提供功能的概念.无论如何,错误是:

Exception in thread "main" java.util.InputMismatchException
    at java.util.Scanner.throwFor(Scanner.java:840)
    at java.util.Scanner.next(Scanner.java:1461)
    at java.util.Scanner.nextDouble(Scanner.java:2387)
    at MyProject.fileInput(MyProject.java:9) <--- Where it happened in our code
    at MyProject.main(MyProject.java:16)

它发生的那一行是在parseDouble上.所以,相反,让我们尝试以不同的方式.我们可以将double作为原始文本,然后将其解析为一个实际的double,如下所示:

    while (readFile.hasNext()) { 
        String name = readFile.next(); 
        String valueStr = readFile.next();
        double value = Double.parseDouble(valueStr); 
        System.out.println(name + " " + value); 
    } 

所以整个完成的程序是:

import java.util.*;
import java.io.*;
public class MyProject { 
    public void fileInput() throws Exception { 
        Scanner readFile = new Scanner(new File("text.txt")); // don't forget to catch FileNotFoundException! 
        readFile.useDelimiter(":|\\n"); 
        while (readFile.hasNext()) { 
            String name = readFile.next(); 
            String valueStr = readFile.next();
            double value = Double.parseDouble(valueStr); 
            System.out.println("Name: " + name);
            System.out.println("Value: " + value);
            System.out.println(""); // blank line
        } 
    }

    public static void main(String[] args) throws Exception {
        MyProject proj = new MyProject();
        proj.fileInput();
    }

所以对于输入文件文本是:

this:1234.5
that:321.0
the other:0.122

输出是

C:\Documents and Settings\glowcoder\My Documents>java MyProject
Name: this
Value: 1234.5

Name: that
Value: 321.0

Name: the other
Value: 0.122


C:\Documents and Settings\glowcoder\My Documents>java MyProject
}