Expressions - The Java Language Specification - page 520

Indeed, the test x!=x is true if and only if the value of x is NaN.
The methods Float.isNaN and Double.isNaN may also be used to test whether a
value is NaN.
• Positive zero and negative zero are considered equal.
For example, -0.0==0.0 is true .
• Otherwise, two distinct floating-point values are considered unequal by the equal-
ity operators.
In particular, there is one value representing positive infinity and one value repres-
enting negative infinity; each compares equal only to itself, and each compares un-
equal to all other values.
Subject to these considerations for floating-point numbers, the following rules then hold
for integer operands or for floating-point operands other than NaN:
• The value produced by the == operator is true if the value of the left-hand operand
is equal to the value of the right-hand operand; otherwise, the result is false .
• The value produced by the != operator is true if the value of the left-hand operand is
not equal to the value of the right-hand operand; otherwise, the result is false .
15.21.2. Boolean Equality Operators == and !=
If the operands of an equality operator are both of type boolean , or if one operand is of type
boolean and the other is of type Boolean , then the operation is boolean equality.
The boolean equality operators are associative.
If one of the operands is of type Boolean , it is subjected to unboxing conversion (§ 5.1.8 ).
The result of == is true if the operands (after any required unboxing conversion) are both
true or both false ; otherwise, the result is false .
The result of != is false if the operands are both true or both false ; otherwise, the result is true .
Thus != behaves the same as ^ (§ 15.22.2 ) when applied to boolean operands.
15.21.3. Reference Equality Operators == and !=
If the operands of an equality operator are both of either reference type or the null type,
then the operation is object equality.