java - Storing file contents to StringBuilder apparently takes too much memory -

i have code:

public static void main(string[] args) {     system.out.println("reading file...");     string content = readfile(args[0]);     system.out.println("done reading file."); }  private static string readfile(string file) throws ioexception {     bufferedreader reader = new bufferedreader( new filereader (file));     string         line = null;     stringbuilder  stringbuilder = new stringbuilder();     while( ( line = reader.readline() ) != null ) {         stringbuilder.append( line );     }      return stringbuilder.tostring(); } 

the readfile method works fine, well, small files.

the thing noticed takes memory.

if open system monitor on windows (ctrl-shift-esc), see java process taking 1,8gb ram, while size of file 550mb.

yes, know, loading file entirely memory isn't idea, i'm doing curiosity.

the program gets stuck @ reading file... when newly created java process starts, takes bunch of mb of ram , goes 1,8gb.

i tried using string concatenation instead of using stringbuilder, have exact same result.

why take memory? final stringbuilder.tostring causing this?

you have remember how these libraries work.

one byte on disk can turn 2 byte char. stringbuilder grows doubling in capacity can twice large need, , need both stringbuilder , string in memory @ same time.

so take example. 550 mb can turn 1100 mb char alone. however, size doubles in size approximately next power of 2 i.e. 2 gb, , on top of string 550 mb.

note: reason not using memory have bug. discarding new lines \r\n means have less characters.

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when processing large file don't have enough memory load memory @ once, better off processing data read it.

btw if have plenty of memory, can read file faster, less memory way.

static string readfile(string file) throws ioexception {     try(fileinputstream fis = new fileinputstream(file)) {          byte[] bytes = new byte[(int) fis.available()];          fis.read(bytes);          return new string(bytes);     } }