error when running code-loop

Can anyone help me please, I cant figure out what I am doing wrong or missing. I need to enter a sentence and write it to a file over and over again until the word done is typed then it should exit the program. please help.

import java.util.*;
import java.io.*;
import java.lang.*;

public class StringtoFile {
	
	public static void main(String[] args) throws IOException
	{
		StringtoFile h = new StringtoFile ();
		
		h.openFile();
		h.addline();
		h.closefile();
	}	
	private Scanner scan, X;
	
	 	public void openFile(){
	 		try{
			 	 X = new Scanner(new File("testFile.txt"));
	 			}
	 		catch(Exception e){
			 System.out.println("You received and Error");
			 
	 		}
	 		}
	
	 	public void addline(){				
	
	 		System.out.println("Enter a Sentence.....");
			String str, casefinish = "done";
				str = X.nextLine();
		
	if(casefinish.equalsIgnoreCase("done")){
		//break;
	}
		else{
			while (str!="done");	
				str = X.nextLine();
	}	
	}
	
	public void closefile(){
		X.close();
	}
}

output:

You received and Error
Enter a Sentence.....
Exception in thread "main" java.lang.NullPointerException
at StringtoFile.addline(StringtoFile.java:31)