What is the difference between a double and a float?

[Matt Kidd]

I keep encountering an error in my programs whenever I have float variables. In debugging the error usually says something along the lines of found a double required a float. I thought if I had a floating point result and I used floating point variables I would get a float as out put i.e float = float * float.

[Anthony Villanueva]

Can you post a simple test case?

[Matt Kidd]

Here is the code:

public class GrossPay {
public static void main (String args[]) {

int counter = 1;
float hoursWorked;
float workRate;
float yourPay;

String s_hoursWorked;
String s_workRate;

DecimalFormat twoDigits = new DecimalFormat("0.00");
while(counter <= 3) {
s_hoursWorked = JOptionPane.showInputDialog("How many hours did you work?");
s_workRate = JOptionPane.showInputDialog("What is your Work rate per hour?");
hoursWorked = Float.parseFloat(s_hoursWorked);
workRate = Float.parseFloat(s_workRate);

if(hoursWorked > 40)
yourPay = ((hoursWorked - 40) * (workRate * 1.5)) + (40 * workRate);
else
yourPay = hoursWorked * workRate;
JOptionPane.showMessageDialog(null, "Your pay is " + yourPay + ".", 
        "Your pay this week", JOptionPane.INFORMATION_MESSAGE);

counter++;
}
System.exit(0);
}
}

Actual error is Found: double Required: float

(Marilyn reformated long line in code)
[ August 09, 2002: Message edited by: Marilyn de Queiroz ]

[Anthony Villanueva]

Hi Matt,
After running the program I discovered 2 things:
1. the literal 1.5 is a double. Use 1.5f instead.
2. I need a raise.

[Matt Kidd]

What makes the compiler believe 1.5 is a double and not a float?

[Anthony Villanueva]

Because of the JLS:

A floating-point literal is of type float if it is suffixed with an ASCII letter F or f; otherwise its type is double and it can optionally be suffixed with an ASCII letter D or d.

[Khurram Shahood(SCJP2)]

hi
with respect to capacity.

[Marilyn de Queiroz]

Originally posted by Matt Kidd:
What makes the compiler believe 1.5 is a double and not a float?

In java the default decimal is a double, not a float. You have to specifically state when you want a float (22.5F)

[Wilfried LAURENT]

Hi Matt,
To be convinced of the difference between float and double ,and the danger in type casting, you can run this simple test program:

public static void main(String[] args)
{
float f=0.95f;
double d=0.95;
    System.out.println("f = "+f);
System.out.println("d = "+d);
System.out.println("d==f?"+ (d==f));
System.out.println("(double)f= "+(double)f);

}

The output ought to be
f = 0.95
d = 0.95
d==f? false
(double)f= 0.949999988079071

[Thomas Markl]

public class GrossPay1 {
  public static void main (String args[]) {
     float hoursWorked = 3.056;
     float workRate = 4.0125;
     float yourPay;
//     double yourPay;
     yourPay = ((hoursWorked - 40) * (workRate * 1.5)) + (40 * workRate);
     System.out.println(yourPay);
   }
}

C:\Java\EigeneJavaProgramme>javac GrossPay1.java
GrossPay1.java:4: possible loss of precision
found : double
required: float
float hoursWorked = 3.056;
^
GrossPay1.java:5: possible loss of precision
found : double
required: float
float workRate = 4.0125;
^
GrossPay1.java:9: possible loss of precision
found : double
required: float
yourPay = ((hoursWorked - 40) * (workRate * 1.5)) + (40 * workRate);
^
3 errors
Why is double found? The input of the yourPay calculation is float so the output to yourpay should
Be float, too and not double.
Thank you very much for your answers.
Thomas

[Peter Kristensson]

yourPay = ((hoursWorked - 40) * (workRate * 1.5)) + (40 * workRate);

Note the "1.5", that's treated as a double, so the whole result returns a double. Use 1.5f instead.

[Anthony Villanueva]

Hi Thomas. The primitive double is like the Borg among other primitive types -- any primtive type that interacts with a double will return a double. For example,
double * float
double * long
double * int
double * short
double * byte'
will return a double result.

[Marilyn de Queiroz]

public class GrossPay1 {
  public static void main (String args[]) {
     float hoursWorked = 3.056F;
     float workRate = 4.0125F;
     float yourPay;
//     double yourPay;
     yourPay = ((hoursWorked - 40F) * (workRate * 1.5F)) + (40F * workRate);
     System.out.println(yourPay);
   }
}

Put 'F' after each literal and it will work. If you have an expression which includes a double and a float, the float will be automatically promoted to a double.

[Matt Kidd]

Thanks everyone...