Streams question / file mapping question

Question

1. I read that I have to close all streams I use. But, on the other hand, in the topic on layering streams (in the same books or tutorials) I see such piece of code:
DataInputStream dis = new DataInputStream(new BufferedInputStream(new FileInputStream("file.txt")));It's obviuos that I can explicitly close only the dis stream object. What obout the rest created along the way?
2. I have this code snippet:
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
public class Main {
    public static void main(String[] args) {
        try {
            FileChannel channel = new FileInputStream("c:\file.txt").getChannel();
            long size = channel.size();
            ByteBuffer buf = channel.map(FileChannel.MapMode.READ_WRITE, 0, size);
            for (long i = 0; i < size; ++i) {
                buf.putChar('a');
        } catch (IOException exc) {
}When the program terminates, the file is not updated. Why is that?
I am using Win XP.
Thanks!

Answer 1

2. Ok, it generated an exception becouse the path was wrong (forgot about double backslach). Here is the code:
package Main;
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
public class Main {
    public static void main(String[] args) {
        try {
            FileChannel channel = new FileInputStream("c:\\file.txt").getChannel();
            long size = channel.size();
            ByteBuffer buf = channel.map(FileChannel.MapMode.READ_WRITE, 0, size);
            for (long i = 0; i < size; ++i) {
                buf.putChar('a');
        } catch (IOException exc) {
            System.out.println("Fuck it, an exception!");
            exc.printStackTrace();
}Now it generates a NonWritableChannelException at line:
ByteBuffer buf = channel.map(FileChannel.MapMode.READ_WRITE, 0, size);I just don't get whats wrong with the code.