Tutorial 19: Reading Text Files

The first thing when you want to read a text file is to actually have one. So go to your desktop or anywhere else on your computer and create a text tile and put some content into it. You can put into it random text and numbers if you like. 

Now go to Java and let’s start reading the file!

I’m going to go step by step and towards the end of the tutorial, I will put everything together so that you can see how everything fits.

The first step is to get the path of your file. In Windows, you can right-click the file and then select Properties. In my case, my file is located at C:\Users\Mukami\Desktop. 

Then, create a String variable to hold the path of your file on your computer. Don’t forget to add the name of your file at the end of the file’s path.

String filePath = “C:\Users\Mukami\Desktop\Document1.txt”;

Now in Windows, the file location contains backslash characters. This is a problem in Java because we know that a backslash character in Java followed by a letter indicates a special format character. This is why we usually have “\n” for newline and “\t” for tab, for example. In other operating systems like Linux, however, the path of the file will contain forward slashes, which is not a problem.

For Windows users, however, you need to change the backslashes to forward slashes to tell Java that you are referring to a file path.

String filePath = “C/Users/Mukami/Desktop/Document1.txt”;

The next step is to create a File object and in its constructor, pass the file’s path, which is contained in the “filePath” variable as follows:

File file1 = new File (filePath);

Then, we create an object of type Scanner and then pass the object file1 of type File to its constructor like this:

 

Scanner scanner1 = new Scanner (file1);

So now, we can create a loop that will read the entire file and print out the contents to the console like this:

while (scanner1.hasNextLine()) {

            String content = scanner1.nextLine();

            System.out.println (content);

}

Finally, we need to close the Scanner object to prevent resource leakage by writing the following line:

scanner.close ();

Don’t forget to add all the necessary import statements.

Notice that scanner1.nextLine(); reads all the content in the file, be it numerical or textual. However, what if we want to read integer values only in the file? We use the Scanner function nextInt(). What if we want to read double values in the file? We use nextDouble(). Here is how we read integers and doubles respectively in the entire text file:

while (scanner1.hasNextLine()) {

            String content = scanner1.nextInt();

            System.out.println (content);

}

while (scanner1.hasNextLine()) {

            String content = scanner1.nextDouble();

            System.out.println (content);

}

Now, we know that the program will look for the file in the specified location. But what is the file doesn’t exist or the file name or file path is wrong? Then it means that unless we do something, the program will crash. To avoid this, we can use a try catch block or we can throw an exception. We will talk about Exceptions and the try catch block in the next tutorial. For this example, we will just throw an exception in the main method of the class like this:

public static void main (String[] args) throws FileNotFoundException {

So now let us put everything together:

public class Person {

            public static void main (String[] args) {

                        String filePath = “C/Users/Mukami/Desktop/Document1.txt”;

File file1 = new File (filePath);

Scanner scanner1 = new Scanner (file1);

while (scanner1.hasNextLine()) {

                                    String content = scanner1.nextLine();

                                    System.out.println (content);

}

while (scanner1.hasNextLine()) {

                                    Integer contentInt = scanner1.nextInt();

                                    System.out.println (content);

}

while (scanner1.hasNextLine()) {

                                    Double contentDouble = scanner1.nextDouble();

                                    System.out.println (content);

}

scanner1.close ();

}

}

The above program produces the output shown in the following screenshot:

Figure1: Screenshot of the contents of a text file read from desktop.

This is one simple way of reading from text files. In another tutorial, I will show you how to read a file in a more comprehensive way, but a way that gives you more control over the process of reading the file.

In case you have any questions or comments, please drop them in the comments section below and I will be more than happy to address them.

Until the next tutorial, take care.