primesfile.java

介绍有关java的资料 课件 相当一本书籍 里面都是很基础的知识

import  java.io.*;
    public class PrimesFile
    {
      RandomAccessFile raf;
      public static void main(String args[])throws IOException
      {
          (new PrimesFile()).createprime(100);
      }

     public void createprime(int max) throws IOException
     {
        raf=new RandomAccessFile("primes.bin", "rw");
        raf.seek(0);
        raf.writeInt(2);
        int  k=3 ;
        while(k<=max)
        {
          if(isPrime(k))
          raf.writeInt(k);
          k=k+2;
        }
        output(max);
        raf.close();
      }

     public boolean isPrime(int k)throws IOException
     {
        int i=0, J ;
        boolean yes=true;
        try
        {
           raf.seek(0);
           int count=(int)(raf.length()/4);
           while((i<=count)&&yes)
          {
            if(k%raf.readInt()==0)
              yes=false ;
            else
              i++;
            raf.seek(i*4);
          }
        }
        catch(EOFException e){}
    
        return yes;
          
     } //方法结束

      
     public void output(int max) throws IOException
     {
       try
         {
            raf.seek(0);
            System.out.println("[2～"+max+"]中有"+(raf.length()/4)+"个素数：");
            for(int i=0;i<(int)(raf.length()/4);i++)
            {
               raf.seek(i*4);
               System.out.print(raf.readInt()+" ");
               if ((i+1)%10==0) System.out.println();
            }
         }
        catch(EOFException e){}
        System.out.println();

      }
     

}