1.Read n
2.lets take variables of type int (i=1,j=1,temp=0,count=0);
3. for (;i<n;i++){
    count=0;
      while(j<=i){
       if((i%j)==0){
        count+=1;
          j++;
         if(count>2)break;
       }
      }
    if(count==2)
     temp=i;
}
4.the value in temp after for loop execution will be the 
Greatest Prime Number

Sorry. initialize i=2 directly as 2 is the first prime 
number.. no need of checking for 1.

<----------------- Import appropriate pkgs ------------->

public class Mainmain 
{
 public static void main(String[] args) throws IOException
 {
 BufferedReader br= new BufferedReader(new
InputStreamReader(System.in));

      System.out.println("Enter the no of nos");
      int n=Integer.parseInt(br.readLine());
      int[] a= new int[n];
      System.out.println("Enter the nos");
      for(int i=0;i<n;i++)
      {
          a[i]=Integer.parseInt(br.readLine());
      }
      Arrays.sort(a);
	  
      LOOP: for(int i=n-1;i>=0;i--)
      {
          int b=2;
          boolean c=true;
          while(b<a[i])
          {
           if((a[i]%b)==0)
              {
                c=false;
                continue LOOP;             
              }
			   b++;
         }
      if(c)
      {
        System.out.println("The largest prime no among the
list is "+a[i]);
        break;
      }
	  
    }
  }
}


<----------------- It Works -------------------------->