Java Scanner won't read

Question

I'm trying to read from a file that has information written in the format: someName:aDoubleNumber and returns the name and the double. I've written the following scanner, but it doesn't work, any ideas why?

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

Answer 1

You're not reading from a file. You're reading the String "text.txt". You need a file first.

    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);
    }

I took the code from your comment and formatted, and I get this

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); 
        } 
    }
}

Now you seem to have a problem - perhaps you meant class FileInput to be public void fileInput() throws Exception ? When I do this, it compiles. Now we need a main() method to run it! So I add this:

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

Now when I ran it I actually got an error. This means there was actually a problem in the code I gave you to begin with. Of course, that code was never intended to be copy/pasted, but was more to give an idea of capability. Anyway, the error is:

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)

The line where it happened was on the parseDouble. So, instead, let's try doing it a different way. We can get the double as a raw piece of text, and then parse it into an actual double like this:

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

So the whole completed program is:

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();
    }

So for the input file text being:

this:1234.5
that:321.0
the other:0.122

The output was

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
}