how delete a specific line in a file in java

[velvet bramble]

how delete a specific line in a file in java

[sturdy tangle]

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[rotund ore]

https://stackoverflow.com/questions/1377279/find-a-line-in-a-file-and-remove-it

this thread has a few examples

make sure u read the comments

[velvet bramble]

Ok then Thank you Sir!

[sturdy tangle]

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[pastel spoke]

you basically copy from the file to change to a temporary file

[velvet bramble]

Check #general

[pastel spoke]

nah, this channel is fine

[velvet bramble]

oh lol

ok gonna resend

[pastel spoke]

so you just copy all lines from the input file to the temporary file except the one you want to remove

[velvet bramble]

But i Don't get it
He open 2 files reader and writer
then what
oh
Ok i think i gonna open file reader
when loop until fine the line
then delete the line
right @pastel spoke | Daniel ?

[pastel spoke]

and then you replace the file to change

[velvet bramble]

bruh i ping the dude 2 times 😭

[velvet bramble]

Yep

[velvet bramble]

this what i saying here ig

[pastel spoke]

not deleting the line but skipping it

The goal is to create a new file with the target content

and then you replace the original file

[velvet bramble]

oh

this only way?

can't i just delete the line

[pastel spoke]

not the only way

[pastel spoke]

No, you can't

the OS doesn't have that concept

The operating system requires files to be continuous

[velvet bramble]

Bufferreader is the OS?

[pastel spoke]

no

[velvet bramble]

oh

[pastel spoke]

OS=operating system

[velvet bramble]

Os is operating system

[pastel spoke]

Java runs on top of the OS

[velvet bramble]

got it

[pastel spoke]

if these are the files

and you want to remove a line

then you need to move all lines after that

the easiest approach is the one from Stack Overflow

[velvet bramble]

Werid way

[pastel spoke]

alternatively, you could find the position of the file to remove

and then move everything up

[velvet bramble]

this will take alot of time to load ;/

Java Is Taking all Class and Load it right not like python that check every line?

ok then

ok

So this how the code gonna work

we Create File

with same name

Then We Copy All Contant

of the old file

to new one

but when we find the line that we want change

we just skip it

and put the new line

[pastel spoke]

I'm working on something with RandomAccessFile

[velvet bramble]

oh

og

oh

This Cool

No need bufferreader and bufferwriter

[pastel spoke]

try(RandomAccessFile file = new RandomAccessFile(yourFilePath, "rw")){
  String line;
  long oldPosition;
  long newPosition=0;
  //find the removed line, we need the start and end of that line
  do{
    oldPosition = newPosition;//start of the line
    line = file.readLine();
    newPosition=file.getFilePointer();//end of the line
  }while(!isThisTheLineToRemove(line));//continue reading without changing anything until you reach the line you want to remove
  
  //move content of the file
  byte[] buffer = new byte[1024];//temporary buffer where be put the stuff to move
  int read;//number of bytes read, this is -1 when the end of the file is reached
  while((read = file.read(buffer))!=-1){//loop until you reach the end of the file and read the content into buffer
    file.seek(oldPosition);//go to the position where you stopped writing - at the beginning, this is the start of the line to remove
    file.write(buffer, 0, read);//take the read data and write it back at the correct position
    oldPosition+=read;//increment both positions
    newPosition+=read;//increment both positions
    file.seek(newPosition);//move to the position you are reading
  }
  file.setLength(oldPosition);//remove the end of the file
}

[velvet bramble]

The guy typing easy

oh

i see

let me read frist

why we need byte[] buffer = new byte[1024];

[pastel spoke]

so you are doing this

[velvet bramble]

oh

[pastel spoke]

let me add a few comments

[velvet bramble]

byte should be 1024?

Ok!

take your time

btw isThisTheLineToRemove( could i just write small part of the line like line = hi= nice could i just write hi=

and it delete the rest of the line?

Sir?

[pastel spoke]

If you want to remove the first line containing REMOVEME, this could be something like !"REMOVEME".equals(line)

(I forgot the ! there - I added it to the code now)

[velvet bramble]

yep

i added .equals

[pastel spoke]

I think the first loop is clear, right?

[velvet bramble]

not frist line like 6 line

[velvet bramble]

ah yes

[pastel spoke]

?

[velvet bramble]

like

i will make if

if they see the line have pvp:

change it do Pvp: true

so

oh

[velvet bramble]

this skip line

i see

i understanding now

[pastel spoke]

after the first line, you have this situation

ignore the one arrow pointing in the wrong direction

[velvet bramble]

toremove = line will remove
old postion = old file
new postion = new file

right?

[velvet bramble]

lol

[pastel spoke]

no, these are positions in the file

the position of the start and end of the line

[velvet bramble]

Oh

I See

this weird

in python you could remove and add text in like 3 lines

Ok anwyays

We Now

find line

skiped line

good

[pastel spoke]

the next step is you copy the next 1024 bytes after the line to a buffer

this is the byte[]

it doesn't need to be 1024 bytes

I just chose that

[velvet bramble]

I see

Amazing

[pastel spoke]

then you take that buffer and move it back to the beginning of the line

[velvet bramble]

file.write(buffer, 0, read);?

oh

[pastel spoke]

this is exactly what this image does

the variable read stores the actual number of bytes that have been read

[velvet bramble]

and this oldPosition+=read; newPosition+=read;

[pastel spoke]

this is the next step

[velvet bramble]

;o

what is the next step

[pastel spoke]

so you have these lines on the right

[velvet bramble]

yep

buffer

wait

no

i mean

old and new postion

[pastel spoke]

you move these positions

[velvet bramble]

ooh

ok

we check all lines

skip line

[pastel spoke]

so that oldPosition points to the end of the stuff you have written

[velvet bramble]

add it so buffer bypte

then make new file

and add it there

i see

[velvet bramble]

i see

[pastel spoke]

and newPosition points where you stopped reading

if you have moved 1024 bytes, you add 1024 bytes to both

[velvet bramble]

yep

now

we removed the line :P

[pastel spoke]

if you have moved 512 bytes, you add 512 bytes to both

but then you are not finished

[velvet bramble]

what is bytes

like

werid

[pastel spoke]

a byte is 8 bits of memory

[velvet bramble]

bruh

so small

[pastel spoke]

you also need to move the remainder of the file

[pastel spoke]

this is why we are moving 1024 bytes at once

[pastel spoke]

so you have 1024*8 bits of memory at once

[velvet bramble]

eh

[pastel spoke]

and then you move the next part of the file

[velvet bramble]

i see

now what next step

[velvet bramble]

oh

we delete the other file?

[pastel spoke]

yeah you just continue

and repeat

you move the rest of the file up

sry I got to go

[velvet bramble]

I see

now you removed the line

:D

Thank you For explain everything

[sturdy tangle]

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