c and d are technically two different objects and == operator compares only references.
c.equals(d)
is better as it compares values, not references. But still not ideal. Comparing floating-point values directly should always take some error (epsilon) into account (Math.abs(c - d) < epsilon).
Note that:
Integer c = 1;
Integer d = 1;
here comparison would yield true, but that’s more complicated (Integer internal caching, described in JavaDoc of Integer.valueOf()):
This method will always cache values in the range -128 to 127, inclusive, and may cache other values outside of this range.
Why valueOf()? Because this method is implicitly used to implement autoboxing:
Integer c = Integer.valueOf(1);
Integer d = Integer.valueOf(1);