Java int, double, float, and mixed-type arithmetic rules

Java FAQ: What are the rules about Java arithmetic (multiplication, division) involving mixed data types?

While working on a math problem in Java just a little while ago, I realized that I wasn’t comfortable with the Java mixed-type division rules. That is, I wondered if the result of this equation:

3 / 2

the same as the result of this equation:

3 / 2.0

or this equation:

3.0 / 2.0
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The answer

The short answer to this problem is this:

All values in an mixed arithmetic operations (+, −, *, /, %) are converted to double type before the arithmetic operation in performed.

I found that answer at this emory.edu url.

As a proof of that statement, here’s the source code for a sample Java arithmetic program:

public class Test1 {

  public static void main (String[] args) {
     System.out.println("3 / 2     = " + (3 / 2));
     System.out.println("3 / 2.0   = " + (3 / 2.0));
     System.out.println("3.0 / 2   = " + (3.0 / 2));
     System.out.println("3.0 / 2.0 = " + (3.0 / 2.0));
  }

}

and here’s the output of that program:

3 / 2     =  1    # not a "mixed" equation
3 / 2.0   =  1.5
3.0 / 2   =  1.5
3.0 / 2.0 =  1.5

Notice that dividing an int by an int in the first example results in an int, and that value isn’t what you might expect. So, as a general rule, it’s important to remember not to use two integer values like that when dividing numbers.

On a related note, this mathbits.com URL makes the following, general statement about Java arithmetic and mixed data types:

When an operation involves two data types, the smaller type is converted to the larger type.

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More Java division and arithmetic rules

The first URL I linked to above shares several other good rules. This first one is about float and double values:

All floating point values (float and double) in an arithmetic operation (+, −, *, /) are converted to double type before the arithmetic operation in performed.

This next rule is about using integer values in arithmetic operations:

All integer values (byte, short and int) in an arithmetic operations (+, −, *, /, %) are converted to int type before the arithmetic operation in performed. However, if one of the values in an arithmetic operation (+, −, *, /, %) is long, then all values are converted to long type before the arithmetic operation in performed.

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Summary

In summary, if you wanted to see how to use Java int, double, float, and other data types in mathematical operations, it’s helpful (and important) to understand these arithmetic rules.

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