out of memory error, java heap space

I try to read log file with more than 4 million lines and size more than 400 MB, but I get Out of Memory Error : java heap space. This is my code :

File file = new File("C:\\file.log");
        FileReader fileReader = new FileReader(file);
        BufferedReader bufferedReader = new BufferedReader(fileReader);
        StringBuilder stringBuffer = new StringBuilder();
        String line;
        while ((line = bufferedReader.readLine()) != null) {
            stringBuffer.append(line);
        }

I tried to increase heap memory to 1GB, but still get that message. What would be the possible cause?