In another Bruce Eckels exercise in calculating velocity, v = s / t where s and t are integers. How do I make it so the division cranks out a float?

class CalcV { float v; float calcV(int s, int t) { v = s / t; return v; } //end calcV
}
public class PassObject { public static void main (String[] args ) { int distance; distance = 4; int t; t = 3; float outV; CalcV v = new CalcV(); outV = v.calcV(distance, t); System.out.println("velocity : " + outV); } //end main
}//end class

1

9 Answers

Just cast one of the two operands to a float first.

v = (float)s / t;

The cast has higher precedence than the division, so happens before the division.

The other operand will be effectively automatically cast to a float by the compiler because the rules say that if either operand is of floating point type then the operation will be a floating point operation, even if the other operand is integral. Java Language Specification, §4.2.4 and §15.17

3

Try:

v = (float)s / (float)t;

Casting the ints to floats will allow floating-point division to take place.

You really only need to cast one, though.

1

Cast one of the integers to a float to force the operation to be done with floating point math. Otherwise integer math is always preferred. So:

v = (float)s / t;

To lessen the impact on code readabilty, I'd suggest:

v = 1d* s/t;

You can cast the numerator or the denominator to float...

int operations usually return int, so you have to change one of the operanding numbers.

1

You can cast even just one of them, but for consistency you may want to explicitly cast both so something like v = (float)s / (float)t should work.

Cast one of the integers/both of the integer to float to force the operation to be done with floating point Math. Otherwise integer Math is always preferred. So:

1. v = (float)s / t;
2. v = (float)s / (float)t;

1

JLS Standard

JLS 7 15.17.2. Division Operator / says:

Integer division rounds toward 0. That is, the quotient produced for operands n and d that are integers after binary numeric promotion (§5.6.2) is an integer value q whose magnitude is as large as possible while satisfying |d · q| ≤ |n|. Moreover, q is positive when |n| ≥ |d| and n and d have the same sign, but q is negative when |n| ≥ |d| and n and d have opposite signs.

This is why 1/2 does not give a float.

Converting just either one to float as in (float)1/2 suffices because 15.17. Multiplicative Operators says:

Binary numeric promotion is performed on the operands

and 5.6.2. Binary Numeric Promotion says:

• If either operand is of type double, the other is converted to double.
• Otherwise, if either operand is of type float, the other is converted to float

Try this:

class CalcV
{ float v; float calcV(int s, int t) { float value1=s; float value2=t; v = value1 / value2; return v; } //end calcV
}

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