Java中的FileWriter缓冲区在哪里？它是在系统空间还是在用户进程空间？

在调用close（）之前，Java的FileWriter缓冲区在哪里？它是在系统空间还是在用户进程空间

public class FlushTest {
    public static void main(String[] args) throws IOException {
        FileReader fileReader = new FileReader("/path/Hello1.txt");
        FileWriter fileWriter = new FileWriter("/path/Hello2.txt");
        int readerCount = 0;
        char[] chars = new char[1024];
        while (-1 != (readerCount = fileReader.read(chars))) {
            fileWriter.write(chars, 0, readerCount);
        }
    }
}