Thread: Fliereader/Filewriter (Need Help!)

Ok so Im trying to make a program in Java that will act as an ATM. What I want it to be able to do is have someone enter a starting balance and then have the ability to withdraw money and deposit money into that account. The hard part is that I want the program to keep that account balance, so even after I close the program, the amount in the balance is still stored. Right now im just doing a little test try out FileWriter and FileReader in Java. So here is my code:

import java.io.*;
import java.util.Scanner;
 
public class Files{
 
	public static void main(String[] args) throws IOException
	{
 
	Scanner input = new Scanner( System.in );
 
	int num;
 
	System.out.print("Enter an integer: ");
		num = input.nextInt();
 
	File f;
	f = new File ("File.txt");
 
	if(!f.exists())
	{
 
		f.createNewFile();
		System.out.println( "New file File.txt has been created" );
 
	}
 
	FileWriter fs = new FileWriter(f);
	BufferedWriter op = new BufferedWriter(fs);
 
	op.write("" + num);
	op.close();
 
	FileInputStream ifs = new FileInputStream(f);
	DataInputStream in = new DataInputStream(ifs);
	BufferedReader br = new BufferedReader(new InputStreamReader(in));
	int str;
 
	while((str = br.readLine() != null))
	{
		System.out.println(str);
	}
 
	in.close();
 
	}
}

I keep getting this error "required : boolean found: int" and "required : int found: boolean" Im assuming it has to do with the line "while((str = br.readLine() !null))

Thanks! :)

import java.io.*;
import java.util.Scanner;
 
public class Files{
 
	public static void main(String[] args) throws IOException
	{
 
	Scanner input = new Scanner( System.in );
 
	int num;
 
	System.out.print("Enter an Integer: ");
		num = input.nextInt();
 
	File f;
	f = new File ("File.txt");
 
	if(!f.exists())
	{
 
		f.createNewFile();
		System.out.println( "New file File.txt has been created" );
 
	}
 
	FileWriter fs = new FileWriter(f);
	BufferedWriter op = new BufferedWriter(fs);
 
	op.write("" + num);
	op.close();
 
	FileInputStream ifs = new FileInputStream(f);
	DataInputStream in = new DataInputStream(ifs);
	BufferedReader br = new BufferedReader(new InputStreamReader(in));
	int str;
 
	while(str == br.readLine())
	{
		System.out.println(num);
	}
 
	in.close();
 
	}
}

I got rid of the != null, since from my understand, null is mostly used for string. I have used this program before for doing almost this same job, but instead of using an integer, I used a String. It worked like a charm, and it printed out the String correctly. This time however, I can get the integer to save to the "File.txt" but it wont reprint the value. After fixing it and recompiling it, I not get the error "Incomparable Types: int and String".