Thread: Editing a Text File in Java, a specific part.

Read all the file into memory, make the changes, write the file back to disk.
If you know the exact location (the displacement from the first byte of the file) of the characters in the file you could use the RandomAccessFile class to overwrite the data, if the new data has the same number of characters as the old data.

BTW Disk files do not have rows and columns, they contain bytes from 0 to the length-1.

Originally Posted by sakonpure6

Let's say I have a map.txt file, and I know what row and column the char I want to change is at. How do I do this?

There's no easy/clean way to do this. It also depends on if you know how many characters are in each line and if this number is the same for all lines. And also if the charset of the file is a single-byte, fixed multi-byte or a variable multi-byte. Without these informations it's quite impossible to think a "random" access to modify a single character.

Other solutions:
1) Read all the content in memory (if possible), change in memory and then rewrite the entire file.
or
2) Read the file in small pieces by time, 1 char by time or 1 line by time and write to a new file changing "on the fly" what you need.

Writing to a file will replace ALL of its old contents if the write is NOT in append mode.
Write a small test program that reads a small file, changes it and writes it out. Look at what was written.