Brady Zhu Brady Zhu - 1 month ago 10
Java Question

What are not 2 Long variables equal with == operator to compare in Java?

I got a very strange problem when I'm trying to compare 2 Long variables, they always show false and I can be sure they have the same number value by debugging in Eclipse:

if (user.getId() == admin.getId()) {
return true; // Always enter here
} else {
return false;
}


Both of above 2 return values are object-type Long, which confused me. And to verify that I wrote a main method like this:

Long id1 = 123L;
Long id2 = 123L;

System.out.println(id1 == id2);


It prints true.

So can somebody give me ideas?. I've been working in Java Development for 3 years but cannot explain this case.

Answer Source

== compares references,equals compares value. This two Long is Object so they compare references.

BUT Long id1 = 123L; will auto be autoboxed to a Long object using Long.valueOf(String) internally,the process will use a LongCache, and 123 is between the LongCache[-128,127] so the are actually the same object.