# LineNumberReader

The Java `LineNumberReader` class (`java.io.LineNumberReader` is a `BufferedReader` that keeps track of line numbers of the read characters. Line numbering begins at 0. Whenever the `LineNumberReader` encounters a line terminator in the characters returned by the wrapped `Reader`, the line number is incremented.

You can get the current line number from the `LineNumberReader` by calling the `getLineNumber()` method. You can also set the current line number, should you need to, by calling the `setLineNumber()` method.

### LineNumberReader Example

Here is a simple Java `LineNumberReader` example:

```
LineNumberReader lineNumberReader = 
    new LineNumberReader(new FileReader("c:\\data\\input.txt"));

int data = lineNumberReader.read();
while(data != -1){
    char dataChar = (char) data;
    data = lineNumberReader.read();
    int lineNumber = lineNumberReader.getLineNumber();
}
lineNumberReader.close();
```

This example first creates a `LineNumberReader`, and then shows how to read all the characters from it, and also shows how to get the line number (for each character read, in fact, which may be a bit more than you need).

### Line Numbers in Parsing

Line number can be handy if you are parsing a text file that can contain errors. When reporting the error to the user, it is easier to correct the error if your error message includes the line number where the error was encountered.

### Closing a LineNumberReader

When you are finished reading characters from the `LineNumberReader` you should remember to close it. Closing a `LineNumberReader` will also close the `Reader` instance from which the `LineNumberReader` is reading.

Closing a `LineNumberReader` is done by calling its `close()` method. Here is how closing a `LineNumberReader` looks:

```
lineNumberReader.close();
```

You can also use the [try-with-resources](https://jenkov.com/java-exception-handling/try-with-resources.html) construct introduced in Java 7. Here is how to use and close a `LineNumberReader` looks with the try-with-resources construct:

```
Reader reader = new FileReader("data/text.txt");

try(LineNumberReader lineNumberReader =
    new LineNumberReader(reader)){

    String line = lineNumberReader.readLine();
    while(line != null) {
        //do something with line

        line = lineNumberReader.readLine();
    }

}
```

Notice how there is no longer any explicit `close()` method call. The try-with-resources construct takes care of that.

Notice also that the first `FileReader` instance is not created inside the try-with-resources block. That means that the try-with-resources block will not automatically close this `FileReader` instance. However, when the `LineNumberReader` is closed it will also close the `Reader` instance it reads from, so the `FileReader` instance will get closed when the `LineNumberReader` is closed.