Thread: Writing to a txt file from the top.

Let's say I have a text file with multiple lines of text. When I read the file and want to write to it, how can I add my text to the top of the file, rather than the bottom (after the original lines of text) ?

This is a system I am trying to create to update my "Map.txt" file after some one picks up a coin , replace the coin with grass.

if(m.getMap(p.getTileX(), p .getTileY() -1) . equals ("c")){
 
						coinCounter ++;
 
						//Read files to change coin position to grass
						try{
							r = new Scanner(new File("res/Map.txt"));
							}catch (Exception e1){ System.out.println("Error Loading Map.txt File."); }
 
						while(r.hasNext()){
 
							for(int i = 0; i < 16; i++){
									level[i] = r.next();
							}
						}
 
						level [p.getTileY()].substring(p.getTileX() - 1 , p.getTileX()).replace ("c" , "g");
 
						r.close();
 
						//Writing back new correct data
 
						try{
						FileWriter fw = new FileWriter("res/Map.txt");
						PrintWriter pw = new PrintWriter(fw);
 
						pw.println();
 
						for(int i = 0; i < 16 ; i++){
							pw.println(level[i]);
						}
 
						}catch (Exception error){}
 
 
 
					 pw.close();
					}

Originally Posted by Norm

Sort of like when you have a pile of books and you want to add some more books at the bottom of the pile.
All the books must be picked up and the new books moved into place and the old books then placed on top.

With the contents of a file, all the existing lines must be copied and saved, the new lines written and the old lines written after the new ones.

Great so lets say I copied all the old code, how do I get rid of the new one in the Map.txt file?

My "Map.tx" has the following:

(Each Line 22 char long)

tttttttttttttttttttttt
tggggggggggggggggggggt
tggggcgggggggggggggggt
tgggggggggggggggcggggt
tgggggggggugggggggcggt
tgggyyyyyguggggggggggt
tgggygcgyggugggggugggt
tgggygggyggggugggugggt
tgggygggygggcggugugggt
tgggygggyggggggggugggt
tgggygggyggggggugggugt
tgygggggggygggguuuuugt
tggyyyyyyygggggugggugt
tggggggggggggggugggugt
tgggggcgggggcggggggggt
tttttttttttttttttttttt

and you see where there is a "c", in my code if my char touches it, I want to replace it with a "g" which stands for grass. Therefore making the coin disappear. Now I think I have accomplished that with my code, but the problem now is to get Java to read my new Map design. Hence, I am trying to write the new Map lines to the same file but starting from the top. ( I have a loop in my project that reads the first 16 lines from Map.txt file, so the rest will be ignored)

okay for example :

ttttcgggttttt

how would you do it with this ?

In accordance with post #7 , I want this to be written in the same file.

ttttggggttttt

exactly.

I know how to read entire lines of text from , column by column (is there a way to copy the text char by char?) . But I do not know how to delete all the useless data in the same .txt file.

What useless data?

Your Map file appears to be of a well-defined structure that could be read into a 2D array and manipulated as needed and then written to the file when necessary.

I've gotten the impression, perhaps incorrectly, that your design requires frequent reading/writing to the file while the game is being played, perhaps in response to each move by the user. If that's the case, don't do that. Read the game board from the file when the game begins, play the game on the game board stored in memory, then write the game board to the file when the game is over. There's no reason for frequent file reading and writing that I can think of. If you think differently, please explain why it's necessary.

Originally Posted by GregBrannon

What useless data?

Your Map file appears to be of a well-defined structure that could be read into a 2D array and manipulated as needed and then written to the file when necessary.

I've gotten the impression, perhaps incorrectly, that your design requires frequent reading/writing to the file while the game is being played, perhaps in response to each move by the user. If that's the case, don't do that. Read the game board from the file when the game begins, play the game on the game board stored in memory, then write the game board to the file when the game is over. There's no reason for frequent file reading and writing that I can think of. If you think differently, please explain why it's necessary.

In my case , I have coins that the user collects. I want to be able to, when the user collects a coin, it's place to be replaced by a grass sprite. This is represented by the char "g" in the map .txt file.