Using java.nio

Question

I have copied this, one program from a book that would have to read file of gives to me to you mixed but it does not work, you could me why?
import java.io.FileInputStream;
import java.io.IOException;
import java.io.File;
import java.io.FileNotFoundException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class ReadPrimesMixedData {
public static void main(String[] args) {
File aFile = new File("C:/Beg Java Stuff/primes.txt");
FileInputStream inFile = null;
try {
inFile = new FileInputStream(aFile);
} catch(FileNotFoundException e) {
e.printStackTrace(System.err);
System.exit(1);
FileChannel inChannel = inFile.getChannel();
try {
ByteBuffer lengthBuf = ByteBuffer.allocate(8);
int strLength = 0; // Stores the string length
ByteBuffer buf = null; // Stores a reference to the second byte buffer
byte[] strChars = null; // Stores a reference to an array to hold the string
while(true) {
if(inChannel.read(lengthBuf) == -1) // Read the string length, if its EOF
break; // exit the loop
lengthBuf.flip();
strLength = (int)lengthBuf.getDouble(); // Extract the length and convert to int
buf = ByteBuffer.allocate(strLength+8); // Buffer for the string & the prime
if(inChannel.read(buf) == -1) {            // Read the string & binary prime value
assert false; // Should not get here!
break; // Exit loop on EOF
buf.flip();
strChars = new byte[strLength]; // Create the array for the string
buf.get(strChars); // Extract string & binary prime value
System.out.println("String length: " + strChars.length+ " String: " +
new String(strChars) + " Binary value: " + buf.getLong());
lengthBuf.clear(); // Clear the buffer for the next read
System.out.println("\nEOF reached.");
inFile.close(); // Close the file and the channel
} catch(IOException e) {
e.printStackTrace(System.err);
System.exit(1);
System.exit(0);
This e' the program that writes the file
import java.io.*;
import java.nio.*;
import java.nio.channels.FileChannel;
public class PrimesToFile2 {
public static void main(String[] args) {
int primesRequired = 100; // Default count
if (args.length > 0) {
try {
primesRequired = Integer.valueOf(args[0]).intValue();
} catch (NumberFormatException e) {
System.out.println("Prime count value invalid. Using default of "
+ primesRequired);
long[] primes = new long[primesRequired]; // Array to store primes
primes[0] = 2; // Seed the first prime
primes[1] = 3; // and the second
// Count of primes found - up to now, which is also the array index
int count = 2;
long number = 5; // Next integer to be tested
outer:
for (; count < primesRequired; number += 2) {
// The maximum divisor we need to try is square root of number
long limit = (long) Math.ceil(Math.sqrt((double) number));
// Divide by all the primes we have up to limit
for (int i = 1; i < count && primes[i] <= limit; i++)
if (number % primes[i] == 0) // Is it an exact divisor?
continue outer; // yes, try the next number
primes[count++] = number; // We got one!
File aFile = new File("C:/Beg Java Stuff/primes.txt");
FileOutputStream outputFile = null;
try {
outputFile = new FileOutputStream(aFile);
} catch (FileNotFoundException e) {
e.printStackTrace(System.err);
System.exit(1);
FileChannel file = outputFile.getChannel();
final int BUFFERSIZE = 100; // Buffer size in bytes
ByteBuffer buf = ByteBuffer.allocate(BUFFERSIZE);
DoubleBuffer doubleBuf = buf.asDoubleBuffer();
buf.position(8);
CharBuffer charBuf = buf.asCharBuffer();
LongBuffer longBuf = null;
String primeStr = null;
for (int i = 0; i < primes.length; i++) {
primeStr = "prime = " + primes; // Create the string
doubleBuf.put(0,(double) primeStr.length());// Store the string length
charBuf.put(primeStr); // Store the string
buf.position(2 * charBuf.position() + 8); // Position for 3rd buffer
longBuf = buf.asLongBuffer(); // Create the buffer
longBuf.put(primes[i]); // Store the binary long value
buf.position(buf.position() + 8); // Set position after last value
buf.flip(); // and flip
try {
file.write(buf); // Write the buffer as before.
} catch (IOException e) {
e.printStackTrace(System.err);
System.exit(1);
buf.clear();
doubleBuf.clear();
charBuf.clear();
try {
System.out.println("File written is " + file.size() + " bytes.");
outputFile.close(); // Close the file and its channel
} catch (IOException e) {
e.printStackTrace(System.err);
System.exit(1);
System.exit(0);
This works correctly

Answer 1

I don't have problems when I compile the program but if I run the program ....I have this
String length: 9 String: prim Binary value: 7277852183226228736
String length: 0 String: Binary value: 162166969980682240
String length: 0 String: Binary value: 7854388801345436928
String length: 0 String: Binary value: 3573983215616
Stjava.lang.IllegalArgumentException
at java.nio.ByteBuffer.allocate(ByteBuffer.java:303)
at ReadPrimesMixedData.main(ReadPrimesMixedData.java:35)
ring length: 0 String: Binary value: 7566167222444367872
String length: 0 String: Binary value: 88089088
String length: 0 String: Binary value: 8214681170873443584
String length: 0 String: Binary value: 1856
String length: 0 String: Binary value: 8070575878335130880
Exception in thread "main"