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Jul 23rd, 2007

Reading numbers from a text file

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I need to read numbers from a text file and then store them in variables to use as input for the Java code I am writing.
The text file will be in this format:
--------------------------------------------------------
5------------- this is the number of nodes
0------------- starting node
0,2,1---------node a,node b, distance from a-b
3,4,5--------- " , " , "
2,6,5
1,4,2
1,5,3
----------------------------------------------------------

Any ideas?

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baltazar

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Jul 23rd, 2007

Re: Reading numbers from a text file

What do you have so far, and what problem is it giving you?

FileReader with BufferedReader and String.split,
or Scanner are good starting points, though.

masijade

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Jul 23rd, 2007

Re: Reading numbers from a text file

I recommend Scanner highly. This will work nicely if:
a. you replace the commas w/spaces and use nextInt()
b. you keep the commas, use next(), and set up an elaborate system to trim the commas out of the Strings made and convert said Strings to ints
I'd go with "a".

Last edited by venomlash; Jul 23rd, 2007 at 11:13 am. Reason: oops

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Jul 23rd, 2007

Re: Reading numbers from a text file

Click to Expand / Collapse Quote originally posted by venomlash ...

I recommend Scanner highly. This will work nicely if:
a. you replace the commas w/spaces and use nextInt()
b. you keep the commas, use next(), and set up an elaborate system to trim the commas out of the Strings made and convert said Strings to ints
I'd go with "a".

You can set the delimeter to any pattern you wish with the useDelimeter() method. You don't need to convert anything prior to scanning.

Ezzaral

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Jul 24th, 2007

Re: Reading numbers from a text file

Ok, so I used Scanner to read input from a text file. I'm trying to test this by just reading in input from a text file and printing it out. But I'm getting some weird errors.

Java Syntax (Toggle Plain Text)
import java.lang.*;
import java.util.*;
 
public class Assignment5
{
	int i = 0;
 
	Scanner st = new Scanner(new File("testCase")).useDelimiter();
	int numNodes = st.nextInt();
	System.out.println(numNodes);
 
 
	while(i <= numNodes)
	{
		Scanner st = new Scanner(new File("testCase")).useDelimiter();
		int k = st.nextInt();
		System.out.println(k);
	}
 
 
	public static void main(String[] args)
	{
		Assignment5 A5 = new Assignment5();
	}//end of main
 
 
}//end of Assignment5 class
import java.lang.*;
import java.util.*;

public class Assignment5
{
	int i = 0;

	Scanner st = new Scanner(new File("testCase")).useDelimiter();
	int numNodes = st.nextInt();
	System.out.println(numNodes);


	while(i <= numNodes)
	{
		Scanner st = new Scanner(new File("testCase")).useDelimiter();
		int k = st.nextInt();
		System.out.println(k);
	}


	public static void main(String[] args)
	{
		Assignment5 A5 = new Assignment5();
	}//end of main


}//end of Assignment5 class

My testCase file is:
5
55
555
5555
55555

The errors I can't seem to figure out are:

Assignment5.java:18: <identifier> expected
System.out.println(numNodes);
^
Assignment5.java:18: <identifier> expected
System.out.println(numNodes);
^
Assignment5.java:21: illegal start of type
while(i <= numNodes);
^
Assignment5.java:21: <identifier> expected
while(i <= numNodes);
^
Assignment5.java:21: <identifier> expected
while(i <= numNodes);
^
5 errors

Last edited by baltazar; Jul 24th, 2007 at 3:40 am. Reason: typo

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Jul 24th, 2007

Re: Reading numbers from a text file

You do not have much of your code inside a method - it's in the class file. Place that code inside a method, either main or another method that you call from main to execute like A5.run() or something.

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Jul 25th, 2007

Re: Reading numbers from a text file

Ah yes, I saw my error. It was a noob mistake.

baltazar

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Jul 25th, 2007

Re: Reading numbers from a text file

I am still confused about how to write the usDelimiter in the scanner.
I need it to read number seperated by commas.
What would the useDelimiter parameter be?
I have tried a couple of things (.useDelimiter(",") and .useDelimiter(,)) but they didn't work
Here is my code:

Java Syntax (Toggle Plain Text)
import java.lang.*;
import java.util.*;
import java.io.File;
 
public class Assignment5
{
	public Assignment5()
	{
		int numNodes = 0;
		Scanner st = null;
		try
		{
			st = new Scanner(new File("testCase.txt")).useDelimiter(",");
			numNodes = st.nextInt();
			System.out.println(numNodes);
		}
		catch(Exception e)
		{
			e.printStackTrace();
		}
 
 
 
		while(st.hasNextInt())
		{
			int k = st.nextInt();
			System.out.println(k+",");
		}
	}
 
 
	public static void main(String[] args)
	{
		Assignment5 A5 = new Assignment5();
	}//end of main
 
 
}//end
import java.lang.*;
import java.util.*;
import java.io.File;

public class Assignment5
{
	public Assignment5()
	{
		int numNodes = 0;
		Scanner st = null;
		try
		{
			st = new Scanner(new File("testCase.txt")).useDelimiter(",");
			numNodes = st.nextInt();
			System.out.println(numNodes);
		}
		catch(Exception e)
		{
			e.printStackTrace();
		}



		while(st.hasNextInt())
		{
			int k = st.nextInt();
			System.out.println(k+",");
		}
	}


	public static void main(String[] args)
	{
		Assignment5 A5 = new Assignment5();
	}//end of main


}//end

baltazar

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Jul 25th, 2007

Re: Reading numbers from a text file

You need to specify the delimiter keeping in mind that its a regular expression pattern. If your input from the file is nothing but numbers separated by ',' without any space in between them, the code posted by you must work.

I am assuming that your code won't work since the delimiter you gave was only a single ',' while your input must have had spaces between the number and comma. (eg. 1, 3, 3). You should have input in this format (1,2,3,4).

If you want your code to work for something like(1, 2, 3,4, 5) :

Java Syntax (Toggle Plain Text)
String sample = "1 ,  2 , 3 ,4,    5";
st = new Scanner(sample).useDelimiter("\\s*,\\s*");
int k;
while(st.hasNextInt())
{
    k = st.nextInt();
    System.out.println(k);
}
String sample = "1 ,  2 , 3 ,4,    5";
st = new Scanner(sample).useDelimiter("\\s*,\\s*");
int k;
while(st.hasNextInt())
{
    k = st.nextInt();
    System.out.println(k);
}

~s.o.s~

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Jul 25th, 2007

Re: Reading numbers from a text file

You should use a BufferedReader to read the lines and then use either String.split() or the Scanner to separate the items for your use. This is exactly what Masijade told you in the first response to your post by the way.

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