LongDoubleConversion
Conversion from long to double may lose precision; use an explicit cast to double if this was intentional

The problem

A cast from long to double may lose precision. Prefer an explicit cast to an implicit conversion if this was intentional.

Consider com.google.protobuf.util.Values which has a method of(double value), and the following example:

// Values.of receives a long, which is implicitly converted to double:
long value = 123L;
Values.of(value);

Prefer this (to make existing behavior explicit):

long value = 123L;
Values.of((double) value);

From JLS §5.1.2:

A widening primitive conversion from int to float, or from long to float, or from long to double, may result in loss of precision - that is, the result may lose some of the least significant bits of the value. In this case, the resulting floating-point value will be a correctly rounded version of the integer value, using IEEE 754 round-to-nearest mode

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("LongDoubleConversion") to the enclosing element.