Java Code:
import java.util.*; 

public class AvgNums { 
  public static void main(String args[]) { 
    Scanner conin = new Scanner(System.in); 
    int count = 0; 
    double sum = 0.0; 
    System.out.println("Enter numbers to average."); 
    // Read and sum numbers. 
    while(conin.hasNext()) { 
      if(conin.hasNextDouble()) { 
        sum += conin.nextDouble(); 
        count++; 
      } 
      else {     String str = conin.next();  
        if(str.equals("done")) break; 
        else { 
          System.out.println("Data format error."); 
          return; 
        } 
      } 
    } 
    System.out.println("Average is " + sum / count); 
  } 
}