CODEWITHSUNDEEP
javafile-io
John
John

Reputation: 449

Java - Scanner.nextLine() skipping even when accounting for new line

I'm trying to read from a file line by line that is tab delimited. Here's an example of a file:

state   0   start
state   5   accept
transition  0   0   1   x   R
transition  1   0   0   x   R

I create a Scanner object for the file and set the delimiter to \t. I loop through the file as long as there is a next line. I want to check whether a line begins with state or transition and then get the following information. In the case of lines that begin with state, I use nextInt() and then next() to obtain 0 and start respectively. The issue then arises of going to the next line and repeating the process. I use nextLine() and that's where things get ugly.

I'm aware that nextLine() does not consume the newline character, so I thought to use it twice and it creates more of an issue it seems. 

Scanner sc = new Scanner(file);
sc.useDelimiter("\t");

while(sc.hasNextLine())
{
    if(sc.next().equals("state") == true)
    {
        int stateNumber = sc.nextInt();
        String state = sc.next();
        sc.nextLine();
    }
    sc.nextLine();
}

That seems to be the relveant code that is creating issues.

Am I misunderstanding how next() works or am i missing something else entirely?

Upvotes: 0

Views: 765

Answers (1)

Tim Biegeleisen
Tim Biegeleisen

Reputation: 521194

One option here would be to simply read in each entire line in one go, and then split by a delimeter (tab) to get the individual components:

which (sc.hasNextLine()) {
    String line = sc.nextLine();
    String[] parts = line.split("\\t");

    if (parts[0].equals("state")) {
        // construct custom object here
    }
}

If you want to stick with your original approach then use this:

while(sc.hasNextLine()) {
    if (sc.next().equals("state")) {
        int stateNumber = sc.nextInt();
        String state = sc.next();
    }

    // consume the entire remaining line, line break included
    sc.nextLine();
}

For those lines containing "state" you were making two calls to nextLine(), which would result in an entire line being lost.

Upvotes: 1

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