While Loop with Sentinel issues

[Amie Mac]

Hello fellow ranchers,

I have been racking my brain on trying to figure out how to write the code for a while loop with a sentinel value which calls a variable (actually I think it will call a get method) from another class. I was able to get it to work when I had the variable in the same class, but when I handed in the assignment my instructor advised that I shouldn't declare the variables in the main program and they should all be in the employee.java file. He also stated that the while loops in my set methods shouldn't be there and be put into the main as well.

So I modified the program and I moved the while loops out of the set methods and I ended up using a while (true) look to get the sentinel value to work. I have read that using the while (true) and calling a break is not best practices so I am not satisfied with the program.

I have turned it in this way, but for my learning purposes, I would like to figure out how to use the while loop like I did in my first submission and not using the while(true). I think that it's an issue of getting the input.nextLine() into the loop somehow so that it will "listen" for the value that is being entered in the console. But every which way I tried, the program gave compile errors. I don't have all the "tries" and the errors... I would have to recreate them if anyone wanted to see that...

Can someone take a look and let me know what is needed in my code to get it to work like my first submitted assignment?

So... here is all the code for what I submitted for my assignment.

This is from my first submitted assignment:

import java.util.Scanner; //program uses class Scanner

public class Payroll
{
	//main method begins execution of Java application
	public static void main(String[] args)
	{
		//create Scanner to obtain input from command window
		Scanner input = new Scanner(System.in);

		// declare variables
		String  firstName = null,   // first name of employee
				lastName = null;  // last name of employee

		double 	hourlyRate = 0.0,  // hourly rate of employee
			   	hoursWorked = 0.0; // hours employee worked

		// make an instance of the employee class
		Employee employee = new Employee(firstName, lastName, hourlyRate, hoursWorked);

		// display welcome message
		employee.displayMessage();
		System.out.println(); // prints a blank line

		// prompt for Employee's First Name (or sentinel value of stop)
		System.out.printf( "Enter Employee's First Name <or type stop to exit>:\n  "); //prompt


		// sentinel controlled while loop to listen for a name or the sentinel value stop
		while (! ( firstName = input.nextLine() ).equalsIgnoreCase( "stop" ) ) { // this initializes the name variable and sentinel stop
			employee.setFirstName(firstName); //sets the first name

			// prompt for Last Name
			System.out.printf("Enter Employee's Last Name\n  "); // prompt
				lastName = input.nextLine(); //read line of text from user
					employee.setLastName(lastName); // sets the last name
				System.out.println(); // prints a blank line

			// prompt for HOURLY RATE
			System.out.printf("Enter " + firstName + " " + lastName + "'s HOURLY RATE:\n  "); // prompt
				hourlyRate = input.nextDouble();  // read value from user
					employee.setHourlyRate(hourlyRate); // sets the hourly rate

			// prompt for HOURS WORKED
			System.out.printf("Enter " + firstName + " " + lastName + "'s HOURS WORKED this week:\n  "); //prompt
				hoursWorked = input.nextDouble();  // read value from user
					employee.setHoursWorked(hoursWorked); // sets the hours worked

		// display Employee Info
		employee.displayEmployeeInfo();

		// loops to ask for the next employee first name
		System.out.printf( "Enter Employee's First Name <or type stop to exit>:\n  " ); //prompt
		input.nextLine();  // reads value from user


		} //end while loop


	} // end main method

} // end class payroll

import java.util.Scanner; //program uses class Scanner

public class Employee
{
	//create Scanner to obtain input from command window
	Scanner input = new Scanner(System.in);

	private String firstName; // first name of employee
	private String lastName; // last name of employee
	private double hourlyRate; // hourly rate of employee
	private double hoursWorked; // hours worked of employee
	private double weeklyPay; // weekly pay of employee

	//constructor of employee to initialize first name, last name, hourly rate, and hours worked
	public Employee( String firstName, String lastName, double hourlyRate, double hoursWorked)
	{
		this.firstName = firstName;
		this.lastName = lastName;
		this.hourlyRate = hourlyRate;
		this.hoursWorked = hoursWorked;
	} // end employee constructor


	// set FIRST NAME
	public void setFirstName(String firstName)	{
		this.firstName = firstName; // store the first name
	}//end set FIRST NAME

	// get FIRST NAME
	public String getFirstName() {
		return this.firstName;
	} // end get FIRST NAME

	// set LAST NAME
	public void setLastName(String lastName) {
		this.lastName = lastName; // store the first name
	}//end set LAST NAME

	// get LAST NAME
	public String getLastName()	{
		return this.lastName;
	} // end get LAST NAME

	//set HOURLY RATE
	public void setHourlyRate(double hourlyRate) {
		this.hourlyRate = hourlyRate; // store the hourly rate

		//while loop if value is not positive
		while ( hourlyRate < 0 ) // verifies if hourly rate is a positive number
		{
			System.out.printf("Enter HOURLY RATE (as a positive number):\n  "); // prompt
			hourlyRate = input.nextDouble();  // read value from user
			this.setHourlyRate(hourlyRate); // sets the hourly rate
		} //end hourly rate while loop
	} // end set HOURLY RATE

	//get HOURLY RATE
	public double getHourlyRate() {
		return this.hourlyRate;
	} // end get HOURLY RATE

	//set HOURS WORKED
	public void setHoursWorked(double hoursWorked) {
		this.hoursWorked = hoursWorked; // store the hourly rate

		//while loop if value is not positive
		while ( hoursWorked < 0 ) // verifies if hourly rate is a positive number
		{
			System.out.printf("Enter HOURS WORKED (as a positive number):\n  "); // prompt
			hoursWorked = input.nextDouble();  // read value from user
			this.setHoursWorked(hoursWorked); // sets the hours worked
		} //end hours worked while loop
	} // end set HOURS WORKED

	//get HOURS WORKED
	public double getHoursWorked() {
		return this.hoursWorked;
	} // end get HOURS WORKED

	//calculate WEEKLY PAY
	public double calcWeeklyPay() {
		weeklyPay = hoursWorked * hourlyRate; // stores weekly pay
		return weeklyPay;
	} // end calculate WEEKLY PAY

	//display EMPLOYEE INFO and WEEKLY PAY
	public void displayEmployeeInfo() {
		System.out.printf("\nEmployee Name:  %s %s\n  Weekly Pay: $%.2f\n\n",
			getFirstName(), getLastName(), calcWeeklyPay() );
		System.out.printf("------------------------------------------------\n"); // prints a dashed line
	} // end method displayEmployeeInfo

	//display a welcome message to the Program user
	public void displayMessage() {
		//Display welcome message
		System.out.printf( "\n\nWelcome to the Payroll Program!\n\n" );
	}	// end method displayMessage


} // end class employee

And this is from the revised submission of the assignment with the while (true) loop:

//Week 4 Payroll Program Part 3:  Modify the Payroll Program so that it uses a class to store and retrieve the employee's name,
//the hourly rate, and the number of hours worked. Use a constructor to initialize the employee information, and a method within
//that class to calculate the weekly pay. Once stop is entered as the employee name, the application should terminate. Make sure
//the program maintains all the functionality required in previous assignments and your source code is readable and well documented.
//Use feedback you have received from the instructor to make any needed modifications.

import java.util.Scanner; //program uses class Scanner

public class PayrollLauncher
{
	//main method begins execution of Java application
	public static void main(String[] args)
	{
		//create Scanner to obtain input from command window
		Scanner input = new Scanner(System.in);

		// make an instance of the employee class
		Employee employee = new Employee("","", 0.0, 0.0);

		// display welcome message
		employee.displayMessage();


		while(true)
		{
			System.out.printf( "Enter Employee's First Name <or type stop to exit>:%n  ");
				employee.setFirstName(input.next());

			if (!employee.getFirstName().equalsIgnoreCase("stop"))
			{
				// prompt for Last Name
				System.out.printf("Enter Employee's Last Name%n  "); // prompt
					employee.setLastName(input.next()); // sets the last name
				System.out.println(); // prints a blank line

				// prompt for HOURLY RATE
				System.out.printf("Enter Employee's HOURLY RATE:%n  "); // prompt
				 	employee.setHourlyRate(input.nextDouble()); // sets the hourly rate
					//while loop if value is not positive
					while ( employee.getHourlyRate() < 0 ) // verifies if hourly rate is a positive number
					{
					System.out.printf("Enter Employee's HOURLY RATE (as a positive number):%n  "); // prompt
						employee.setHourlyRate(input.nextDouble()); // sets the hourly rate
					} //end hourly rate while loop

				// prompt for HOURS WORKED
				System.out.printf("Enter Employee's HOURS WORKED this week:%n  "); //prompt
					employee.setHoursWorked(input.nextDouble()); // sets the hours worked
						//while loop if value is not positive
						while ( employee.getHoursWorked() < 0 ) // verifies if hourly rate is a positive number
						{
						System.out.printf("Enter HOURS WORKED (as a positive number):%n  "); // prompt
						employee.setHoursWorked(input.nextDouble()); // sets the hours worked
						} //end hours worked while loop

			// display Employee Info
			employee.displayEmployeeInfo();


			} //end if
		else
			break;
		} //end while


	} // end main method

} // end class PayrollLauncher

//Week 4 Payroll Program Part 3:  Modify the Payroll Program so that it uses a class to store and retrieve the employee's name,
//the hourly rate, and the number of hours worked. Use a constructor to initialize the employee information, and a method within
//that class to calculate the weekly pay. Once stop is entered as the employee name, the application should terminate. Make sure the
//program maintains all the functionality required in previous assignments and your source code is readable and well documented.
//Use feedback you have received from the instructor to make any needed modifications.


public class Employee
{
	private String firstName; // first name of employee
	private String lastName; // last name of employee
	private double hourlyRate; // hourly rate of employee
	private double hoursWorked; // hours worked of employee
	private double weeklyPay; // weekly pay of employee


	//constructor of employee to initialize first name, last name, hourly rate, and hours worked
	public Employee( String firstName, String lastName, double hourlyRate, double hoursWorked )
	{
		this.firstName = firstName;
		this.lastName = lastName;
		this.hourlyRate = hourlyRate;
		this.hoursWorked = hoursWorked;
	} // end employee constructor


	// set FIRST NAME
	public void setFirstName(String firstName)
	{
		this.firstName = firstName;
	}//end set FIRST NAME

	// get FIRST NAME
	public String getFirstName()
	{
		return this.firstName;
	} // end get FIRST NAME

	// set LAST NAME
	public void setLastName(String lastName)
	{
		this.lastName = lastName;
	}//end set LAST NAME

	// get LAST NAME
	public String getLastName()
	{
		return this.lastName;
	} // end get LAST NAME

	//set HOURLY RATE
	public void setHourlyRate(double hourlyRate)
	{
		this.hourlyRate = hourlyRate;
	} // end set HOURLY RATE

	//get HOURLY RATE
	public double getHourlyRate()
	{
		return this.hourlyRate;
	} // end get HOURLY RATE

	//set HOURS WORKED
	public void setHoursWorked(double hoursWorked)
	{
		this.hoursWorked = hoursWorked;
	} // end set HOURS WORKED

	//get HOURS WORKED
	public double getHoursWorked()
	{
		return this.hoursWorked;
	} // end get HOURS WORKED

	//calculate WEEKLY PAY
	public double calcWeeklyPay()
	{
		weeklyPay = hoursWorked * hourlyRate;
		return weeklyPay;
	} // end calculate WEEKLY PAY

	//display EMPLOYEE INFO and WEEKLY PAY
	public void displayEmployeeInfo()
	{
		System.out.printf("%nEmployee Name:  %s %s%n  Weekly Pay: $%.2f%n%n",
			getFirstName(), getLastName(), calcWeeklyPay() );
		System.out.printf("------------------------------------------------%n"); // prints a dashed line
	} // end method displayEmployeeInfo

	//display a welcome message to the Program user
	public void displayMessage()
	{
		System.out.printf( "%n%nWelcome to the Payroll Program!%n%n" );
	}	// end method displayMessage


} // end class Employee

[Amie Mac]

To make things a bit clearer (hopefully), it is these lines that I would like to get working in the rework of the program where I used the while (true):

// sentinel controlled while loop to listen for a name or the sentinel value stop
        while (! ( firstName = input.nextLine() ).equalsIgnoreCase( "stop" ) ) { // this initializes the name variable and sentinel stop
            employee.setFirstName(firstName); //sets the first name

[Carey Brown]

I don't have any problems with your revised code. What's not working for you? Errors? Incorrect output?

[Knute Snortum]

There are a lot of opinions on this, so I'll just tell you mine.

Generally, I like to use do/while loops if I'm going to do something at least once. This will avoid the "printing the prompt twice" issue you have.

Second, I wouldn't set the employee name when I know it's incorrect. So create some kind of input variable to test.

Now, if you have the outer do/while loop and an input variable, what ends the loop? I think you know.

There are two camps on the use of break. One says never use it. I think that's a bit extreme. I wouldn't have a problem with this:

do {
  // prompt
  String input = in.next();
  if ("stop".equalsIgnoreCase(input)) { 
    break;
  }
  //...
} while(...);

This is just an example. You can do it other ways too.

[Amie Mac]

Carey Brown wrote:I don't have any problems with your revised code. What's not working for you? Errors? Incorrect output?

Nothing is necessarily wrong with the revised code. It works as expected. I was just wondering if there is a better way to write it.

[Liutauras Vilda]

I know that assignment marking grids has line "is code clearly commented...", but that is the way too much.

// set FIRST NAME
public void setFirstName(String firstName)

You did good on choosing very clear class, methods, variables names and it is more important than comments, especially when they don't say anything new than code itself.
In practice never comment each line of code - it makes code unreadable.

[Paul Clapham]

Amie Mac wrote:Nothing is necessarily wrong with the revised code. It works as expected. I was just wondering if there is a better way to write it.

When I was a beginner I thought that form of while-loop with the side-effect of assigning a String to a variable was kind of icky. But it's a common idiom and people do get used to it once they've seen it a few times. So I would leave it that way.

[Campbell Ritchie]

Paul Clapham wrote: . . . that form of while-loop with the side-effect of assigning a String to a variable . . .

Agree with Paul C: that is a common idiom. But it does read strangely when you first see it, and you would never guess it if nobody showed you how to do it.

[Amie Mac]

Knute Snortum wrote:There are a lot of opinions on this, so I'll just tell you mine.

Generally, I like to use do/while loops if I'm going to do something at least once. This will avoid the "printing the prompt twice" issue you have.

Second, I wouldn't set the employee name when I know it's incorrect. So create some kind of input variable to test.

Now, if you have the outer do/while loop and an input variable, what ends the loop? I think you know.

There are two camps on the use of break. One says never use it. I think that's a bit extreme. I wouldn't have a problem with this:

do {
  // prompt
  String input = in.next();
  if ("stop".equalsIgnoreCase(input)) { 
    break;
  }
  //...
} while(...);

This is just an example. You can do it other ways too.

Yes, I like this do... while loop better than the while (true) loop that I have in my code. I will have to try it out this way at some point. Thanks for your input.

[Amie Mac]

Liutauras Vilda wrote:I know that assignment marking grids has line "is code clearly commented...", but that is the way too much.

// set FIRST NAME
public void setFirstName(String firstName)

You did good on choosing very clear class, methods, variables names and it is more important than comments, especially when they don't say anything new than code itself.
In practice never comment each line of code - it makes code unreadable.

Yes, I don't like all the comments in the code either, because it does make it harder to read... I just wanted to make sure it was clearly commented.
Thanks for the tip!

[Amie Mac]

Campbell Ritchie wrote:

Paul Clapham wrote: . . . that form of while-loop with the side-effect of assigning a String to a variable . . .

Agree with Paul C: that is a common idiom. But it does read strangely when you first see it, and you would never guess it if nobody showed you how to do it.

Thank you Paul and Campbell... I am glad that there are places out there like Code Ranch that can assist with code writing since the textbooks don't have all the examples.

[Campbell Ritchie]

You're welcome

By the way: do you understand the syntax of that loop and why there have to ybe certain () in certain places?
A style thing: you should not usually have those spaces after ( or before ). We have some style suggestions of our own.

[Amie Mac]

Campbell Ritchie wrote:You're welcome

By the way: do you understand the syntax of that loop and why there have to ybe certain () in certain places?

Do you mean the () in this part of the loop code?

String input = in.next();

Do the () mean that it is a method and arguments or parameters can be passed to the method?

A style thing: you should not usually have those spaces after ( or before ). We have some style suggestions of our own.

Thank you. I read through these style suggestions and in there it is suggested to not use do... while loops.

[Campbell Ritchie]

You got that bit right, but I actually meant the next pair of () outside that.
[Edit]Also, I meant in the line beginning while. Look in your first post, Payroll class, line 30.

[Amie Mac]

Campbell Ritchie wrote:You got that bit right, but I actually meant the next pair of () outside that.
[Edit]Also, I meant in the line beginning while. Look in your first post, Payroll class, line 30.

Do you mean this line?

  while (! ( firstName = input.nextLine() ).equalsIgnoreCase( "stop" ) ) {

I think that we have 3 methods here:
while()
input.nextLine()
equalsIgnoreCase()

but I am not sure why there are () around firstName = input.nextLine(). Is it because of the "!" ?

[Carey Brown]

Amie Mac wrote:

  while (! ( firstName = input.nextLine() ).equalsIgnoreCase( "stop" ) ) {

I think that we have 3 methods here:
while()
input.nextLine()
equalsIgnoreCase()

but I am not sure why there are () around firstName = input.nextLine(). Is it because of the "!" ?

You need those () because the assignment (=) operator has a lower precedence and you want the assignment to take place before the call to equalsIgnoreCase().

[Amie Mac]

Carey Brown wrote:

Amie Mac wrote:

  while (! ( firstName = input.nextLine() ).equalsIgnoreCase( "stop" ) ) {

I think that we have 3 methods here:
while()
input.nextLine()
equalsIgnoreCase()

but I am not sure why there are () around firstName = input.nextLine(). Is it because of the "!" ?

You need those () because the assignment (=) operator has a lower precedence and you want the assignment to take place before the call to equalsIgnoreCase().

Ahh... yes. That makes sense.
Thanks

[Campbell Ritchie]

That was what I wanted to know that you understood.

[Liutauras Vilda]

And I found this page (<- link) most easy readable about operator precedence.
So you could find all of them there.

[Amie Mac]

Liutauras Vilda wrote:And I found this page (<- link) most easy readable about operator precedence.
So you could find all of them there.

Thanks.

I didn't really think about that assignment being an operator and needing precedence.