Help with Sentinel Loops

[hedwards09]

Hello,

I am in an intro to Java programming class and I'm having a little trouble constructing a Sentinel loop that prompts the user for the name of a file until the user inputs "stop" to quit.

Can anyone help me. All help will be much appreciated.

[r035198x]

What have you done so far?

[hedwards09]

public static void main(String[] args)
{
Scanner input = new Scanner(System.in);

String fName;

System.out.print("Enter file name or stop to quit");
fName = input.nextLine();

while (fName != "stop")
{
//Methods entered here
}
}

[r035198x]

Never compare strings using == or !=. Use the equals method instead.
Since you need the user to keep entering values, there needs to be some input.nextLines inside your loop as well.

[hedwards09]

So would the sentinel loop look like this?

while(!fName.equals("stop");
{
input.nextLine();
// methods entered here
}

[Addez]

however == and != works fine when your comparing chars

[r035198x]

It's a start. You also have the compiler and run time with you to test things out, right?

[hedwards09]

Yes i do. In the sentinel loop can I add methods to be executed if the statement returned is false?

[r035198x]

however == and != works fine when your comparing chars

The more general thing to say is that they compare equality of references.
All primitive references hold the actual value they represent so operators work as expected on primitives (of which char is one of them).

Strings are not primitives so their references do not hold the string value but instead point to an object in memory. To compare between those objects you would need to use the overridden equals method.

[r035198x]

Yes i do. In the sentinel loop can I add methods to be executed if the statement returned is false?

You could test that out on the compiler since you say that you have it.





... methods are not added into loops though, they are added into classes.

[hedwards09]

Sorry I phrased that wrong. I can call methods in the sentinel loop. Am I correct?

[r035198x]

Sorry I phrased that wrong. I can call methods in the sentinel loop. Am I correct?

Only one way to find out ...