Java program needed !!

[kickerman97]

If someone could help me, i would appreciate it. I am new to Java and need some help. I need to write a multithreaded java or pthreads program that outputs prime numbers. The user needs to run the program and enter a number on the command line. The program needs to create a seperate thread that outputs all the prime numbers less than or equal to the number that the user entered. Thanks in advance......

[HaganeNoKokoro]

//Main Program Primes.java
import java.io.*;

public class Primes {
	public static void main(String args[]) {
		try {
			PrimeThread pt=null;
			
			//read in parameters
			BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
			System.out.print("Enter a number> ");
			int limit=Integer.parseInt(br.readLine());
			System.out.print("Enter a file name to store the results> ");
			String fName=br.readLine();
			
			//create PrimeThread
			if(fName.length()>0) pt=new PrimeThread(limit, new FileOutputStream(fName)); //output to file
			else pt=new PrimeThread(limit); //output to standard output stream
			pt.run(); //run the thread
		} catch(Exception e) { //implement better exception handling than this
			e.printStackTrace();
		}
	}
}

//Thread class PrimeThread.java
import java.io.*;

class PrimeThread extends Thread {
	private PrintStream pOut=null;
	private int limit=0;
	
	//default constructor. does nothing
	public PrimeThread() {
	}
	
	//constructor to set the number below which to generate primes
	//no output stream is specified, so it outputs to the System.out
	public PrimeThread(int l) {
		limit=l;
		try {
			pOut=System.out;
		} catch(Exception e) {
			e.printStackTrace();
		}
	}
	
	//constructor that sets both the number, as above, and specifies an output stream
	//if the specified stream is null, uses System.out
	public PrimeThread(int l, OutputStream outS) {
		limit=l;
		try {
		    if(outS!=null) {
				pOut=new PrintStream(outS);
			} else {
				pOut=System.out;
			}
		} catch(Exception e) {
			e.printStackTrace();
		}
	}
	
	//method that performs the work of the thread, in this case the generation of prime numbers.
	public void run() {
		//compute primes via the seive
		boolean numbers[]=new boolean[limit+1];
		numbers[0]=false; //need to set 0 not prime
		numbers[1]=false; //need to set 1 not prime
		for(int i=2; i<numbers.length; i++) { //initially set all other numbers potentially prime
			numbers[i]=true;
		}
		for(int i=2; i<numbers.length; i++) {
			if(numbers[i]) { //if this number has been eliminated, so have its multiples
				for(int j=(2*i); j<numbers.length; j+=i) { //eliminate multiples of the current number
					numbers[j]=false;
				}
			}
		}
		for(int i=0; i<numbers.length; i++) { //output the numbers found to be prime
			if(numbers[i]) pOut.println(i);
		}
	}
}

[kickerman97]

thanks alot. Can you show me what to change to make it display the reults on the screen instead of asking for a file to save them in? Thanks again

[HaganeNoKokoro]

When it asks for a file name just hit enter.

[kickerman97]

one other thing, can I put it all in one file instead of two?

[HaganeNoKokoro]

I would imagine it would be ok if you put the PrimeThread class in the Primes.java file.

[kickerman97]

O.k....but I don't want it to ask for a file........

[HaganeNoKokoro]

This sounds like a school assignment, and I've already done waaay too much.

There is another constructor for the PrimeThread class that will not require a file name, and it should be easy enough for you to look through the 25 or so lines of code in Primes.java and remove the part where it asks for a file name.

You can do it! I believe in you! Insert generic inspirational encouragement here!

[kickerman97]

you don't have to help anymore if you don't want to, but I can assure you its not a school assignment.
by-the-way....thanks alot

[HaganeNoKokoro]

What's the purpose then?

[ray326]

Multiple threads writing to the same unsynchronized output stream isn't a good idea anyway.

[HaganeNoKokoro]

So wrap all the print statments in synchronized blocks... not hard to do.