Answer by Jon Skeet for Difference between double and Double in comparison

When applied to expressions of a class type, == will always perform a reference comparison (JLS section 15.21.3). So this line:

System.out.println(c == d); 

is checking whether c and d refer to the same objects. Auto-boxing in Java always (I believe) creates a new object for float and double (the situation is more complicated for integral types¹). Therefore c and d refer to different objects, and so it prints false.

If you want to compare objects for equality, you need to call equals explicitly:

System.out.println(c.equals(d));

With double, it's using numeric equality instead - as specified in section 15.21.1. Hence the difference in behaviour.

¹ For integral autoboxing, "small" values are cached - so autoboxing 5 (say) will return the same reference every time. The definition of "small" is implementation-specific, but it's guaranteed within the range -128 to 127. See the bottom of section 5.1.7 for details.