5.6.2 Binary Numeric Promotion

When an operator applies binary numeric promotion to a pair of operands, each of which must denote a value of a numeric type, the following rules apply, in order, using widening conversion (§5.1.2) to convert operands as necessary:

• 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.
• Otherwise, if either operand is of type long, the other is converted to long.
• Otherwise, both operands are converted to type int.

Binary numeric promotion is performed on the operands of certain operators:

• The multiplicative operators *, / and % (§15.16)
• The addition and subtraction operators for numeric types + and - (§15.17.2)
• The numerical comparison operators <, <=, >, and >= (§15.19.1)
• The numerical equality operators == and != (§15.20.1)
• The integer bitwise operators &, ^, and | (§15.21.1)
• In certain cases, the conditional operator ? : (§15.24)

An example of binary numeric promotion appears above in §5.1. Here is another:

class Test {
	public static void main(String[] args) {
		int i = 0;
		float f = 1.0f;
		double d = 2.0;


		// First i*f promoted to float*float, then
		// float==double is promoted to double==double:
		if (i * f == d)
			System.out.println("oops");


		// A char&byte is promoted to int&int:
		byte b = 0x1f;
		char c = 'G';
		int control = c & b;
		System.out.println(Integer.toHexString(control));


		// A int:float promoted to float:float:
		f = (b==0) ? f : 4.0f;
		System.out.println(1.0/f);

	}

}

which produces the output:

7
0.25

The example converts the ASCII character G to the ASCII control-G (BEL), by masking off all but the low 5 bits of the character. The 7 is the numeric value of this control character.

O suns! O grass of graves! O perpetual transfers and promotions!
—Walt Whitman, Walt Whitman (1855) in Leaves of Grass