How to detect new line(or empty line) in a file?

Question

I'm trying to write a program, which reads text from a file that is specified by the user. Now, this program should detect an empty line.

This is what I have unsuccessfully tried:

public static void editFile(String filePath) throws FileNotFoundException, IOException {
    file = new File(filePath);
    if(file.exists()) {
        fileRead = new FileReader(file);

        bufferedReader = new BufferedReader(fileRead);

        String line = bufferedReader.readLine();
        System.out.println(line);
        while(line != null) {
            line = bufferedReader.readLine();
            if(line == "") {
                //line = null;
                System.out.println("a");
            }
            System.out.println(line);
        }
    }
}

To be more clear:

If I'm passing in a text file with for example this text:

test1
test2

test3

test4

it should print 2 a's in the console because of the empty spaces, but it doesn't.

Thank you for your time, I am glad for any suggestion you may have.

What is the exact output? Does it still print the newlines? Have you tried debugging? — D. Ben Knoble, Aug 14 '15 at 20:45

score 1 · Answer 1 · edited May 23 '17 at 11:58

1

This is because the comparison is wrong. You can't use == to compare two strings, you need to use the equals method:

if(line.equals(""))

Since you are checking for empty string, you can also write

if(line.isEmpty())

How do I compare strings in java?

edited May 23 '17 at 11:58

Community

1
1

answered Aug 14 '15 at 20:50

BackSlash

21,927
22
96
136

score 1 · Answer 2 · answered Aug 14 '15 at 21:02

BackSlash is entirely correct, and has answered your question. I'd like to add that your code has some errors:

You're not closing the Reader
You're not testing the first line for blank
You're processing the null value when reaching EOF

The following corrects these errors.

public static void editFile(String filePath) throws IOException
{
    File file = new File(filePath);
    if (file.exists())
    {
        BufferedReader bufferedReader = new BufferedReader(new FileReader(file));
        try
        {
            String line;
            while ((line = bufferedReader.readLine()) != null)
            {
                if (line.isEmpty())
                {
                    //line = null;
                    System.out.println("a");
                }
                System.out.println(line);
            }
        } finally {
            bufferedReader.close();
        }
    }
}

Output is:

test1
test2
a

test3
a

test4

Note: You're still printing the blank line in addition to the "a".

score 0 · Answer 3 · answered Aug 14 '15 at 21:00

What you're doing wrong is that you're comparing the variable itself, not its value with a null string. Generally there are built-in functions in the string class that return true & false for checking if it's == with something.

if(line.equals("")) { ... }

Or you can just use any alternative way.

How to detect new line(or empty line) in a file?

3 Answers3