FULL PRODUCT VERSION :
Since JDK 9.

ADDITIONAL OS VERSION INFORMATION :
Unrelated to OS.

A DESCRIPTION OF THE PROBLEM :
public class Temp {
	public static void main(String[] args) {
		final Long a = 121L;
		System.out.println(a);
	}
}

javap -v Temp (partial result)
         0: ldc2_w        #2                  // long 121l
         3: invokestatic  #4                  // Method java/lang/Long.valueOf:(J)Ljava/lang/Long;

Compiling this code reveals that the class generated by javac uses Long.valueOf(121L).

JLS 9 in 5.1.7. Boxing Conversion says (this part was changed in this version of JLS):
"If the value p being boxed is the result of evaluating a constant expression (��15.28) of type boolean, char, short, int, or long, and the result is true, false, a character in the range '\u0000' to '\u007f' inclusive, or an integer in the range -128 to 127 inclusive, then let a and b be the results of any two boxing conversions of p. It is always the case that a == b."
so the  value 121L should always be cached.

However, javadoc for Long.valueOf(long) says:
" Note that unlike the corresponding method in the Integer class, this method is not required to cache values within a particular range."

This is a bug for javac to use a method which does not guarantee caching where the value MUST be cached according to JLS.

It is a bug either in javac or a wrong documentation of Long.valueOf(long)


REGRESSION.  Last worked in version 8u172

ADDITIONAL REGRESSION INFORMATION: 
JLS was changed between version 8 and 9.
Under JLS 8 it was not required to cache Longs so this was not a bug.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
As in the description.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A method that guarantees caching is used for boxing conversion of longs.

More practical solution: adjust javdoc of Long.valueOf(long) to say it guarantee caching.
ACTUAL -
As in the description.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class Temp {
	public static void main(String[] args) {
		final Long a = 121L;
		System.out.println(a);
	}
}

---------- END SOURCE ----------