为什么 ThreadLocal 或 AnnotationProcessor 没有在 Java 规范中定义？

Question

For a long time, I have been an application developer in java. Recently, Java and JVM specification piqued my interest. I wanted to know more about some of the internals of java on topics that eluded me for a long time.

I tried searching for ThreadLocal or Annotation Processors in those documents and I couldnt find them. Is there a reason behind dearth of information regarding them? I thought Threadlocal atleast was part of Java packages?

Are specifications not encyclopedias that I imagined them to be? They are fairly huge documents, so I might have missed them completely

https://docs.oracle.com/javase/specs/jvms/se8/jvms8.pdf https://docs.oracle.com/javase/specs/jls/se8/jls8.pdf

Answer 1

Why aren't ThreadLocal or AnnotationProcessor defined in the Java Language Specification (JLS)?

Because they are specified somewhere else.

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The specification for ThreadLocal is in the javadocs:

• https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/ThreadLocal.html

The specifications for annotation processors are also in the javadocs. Start here:

• https://docs.oracle.com/en/java/javase/11/docs/api/java.compiler/javax/annotation/processing/package-summary.html
• https://docs.oracle.com/en/java/javase/11/docs/api/java.compiler/javax/annotation/processing/Processor.html

In general, the JLS only specifies the Java programming language itself. Other aspects of the Java environment such as the Java class libraries, the JVM specifications, the Java tool specifications, and many other things are specified (or described) in various technical notes, white papers and JSRs or JEPs.

In general, all of this information is on the public web, and can be found using Google and intelligently chosen search terms. For example, I got the javadocs of ThreadLocal in Java 11 by Googling for javadoc ThreadLocal java 11 .

However, if you are looking for internal documentation (eg some design document that explains how ThreadLocal is implemented) you are unlikely to find anything ... beyond the OpenJDK source code itself. But the source code is freely available and (generally speaking) well commented. Google for the version you are looking for; eg openjdk source code java 11 .