rt.jar com.sun.istack.internal packages

Question

jre comes with many libraries in rt.jar one of which is com.sun.istack.internal*. I needed the documentation of com.sun.istack.internal.Nullable(which I found being used by google in its CacheBuilder) and first I thought was to go to docs.oracle.com to find its documentation and there I found nothing about it. Next went to source folder sourced with jdk and I didn't find com name entity in the said folder. Next I take a look at the jre7 release and take a look at all the packages and class and found no mention of Nullable there. Though SO had one mention of it, but nothing concrete. I am still puzzled where to get its documentaion and src if needed. I even looked legacy sun api documentation at oracle but nothing mentioned about it. where does oracle document there policy about ported packages and their being standard or not-standard.They must have documented it somewhere it is just that I'm taking too much of time to get there.

Please point me there.

EDIT: Actually the javax.annotation.Nullable is being used in google CacheBuilder and not com.sun.istack.internal.Nullable. Also for someone who may face this issue: javax.annotation.Nullable is not part of Java SE as of now, and it is being ported in jsr305 jar. So if you are planning to use CacheBuilder or just going through its code, do add jsr305 jar in your class path, else eclipse get confuse and will point you to com.sun.istack.intenal.Nullable when ever you hover your cursor over Nullable.

Answer 1

Guava doesn't use com.sun.istack.internal.Nullable. Everything that is not documented in the official Java SE javadoc is internal code, and should not be used in applications.

You're probably looking for javax.annotation.Nullable, which is part of JSR305.

Answer 2

Here is a link to the source code:

• http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/8u40-b25/com/sun/istack/internal/Nullable.java/

(This link may break in the future, but you should be able to find an equivalent using a Google search.)

The reason that you can't find the source code or javadocs in the standard JDK / JRE distributions is that this is a INTERNAL class. There is a long-standing Oracle / Sun policy of discouraging developers from writing code that is dependent on Java internal classes.

FWIW - this is just an annotation, and the meaning is pretty much what the class name implies.

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UPDATE - Apparently, the real cause of this confusion is that you didn't include the JSR305 jar in your buildpath. It is a dependency for CacheBuilder. Eclipse classname completion is then doing its best ... but failing.