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Replace first line of a text file in Java
Java - Find a line in a file and remove
I am trying to find a way to remove the first line of text in a text file using java. Would like to use a scanner to do it...is there a good way to do it without the need of a tmp file?
Thanks.
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Scanner fileScanner = new Scanner(myFile); fileScanner. nextLine(); This will return the first line of text from the file and discard it because you don't store it anywhere.
C Programming from scratch- Master C ProgrammingRead each line of the file Store it in a Sting say input. Try to add this String to the Set object. If the addition is successful, append that particular line to file writer. Finally, flush the contents of the FileWriter to the output file.
Deleting a text line directly in a file is not possible. We have to read the file into memory, remove the text line and rewrite the edited content. Although, of course, it isn't necessary that the entire file fits into memory, as you can read and write in the same loop.
Invoke the replaceAll() method on the obtained string passing the line to be replaced (old line) and replacement line (new line) as parameters. Instantiate the FileWriter class. Add the results of the replaceAll() method the FileWriter object using the append() method.
If your file is huge, you can use the following method that is performing the remove, in place, without using a temp file or loading all the content into memory.
public static void removeFirstLine(String fileName) throws IOException {
RandomAccessFile raf = new RandomAccessFile(fileName, "rw");
//Initial write position
long writePosition = raf.getFilePointer();
raf.readLine();
// Shift the next lines upwards.
long readPosition = raf.getFilePointer();
byte[] buff = new byte[1024];
int n;
while (-1 != (n = raf.read(buff))) {
raf.seek(writePosition);
raf.write(buff, 0, n);
readPosition += n;
writePosition += n;
raf.seek(readPosition);
}
raf.setLength(writePosition);
raf.close();
}
Note that if your program is terminated while in the middle of the above loop you can end up with duplicated lines or corrupted file.
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