Are there any Java Class Library "header files" containing all method descriptors in the standard library?

Question

In order to create a valid .class file, every method has to have a full internal name and type descriptors associated with it. When procedurally creating these, is there some sort of lookup table one can use (outside of Java, where a ClassLoader can be used) to get these type descriptors from a method name? For example, how would one go from Scanner.hasNextByte to boolean java.util.Scanner.hasNextByte(int) / boolean java.util.Scanner.hasNextByte() (or even from java.util.Scanner.hasNextByte to boolean java.util.Scanner.hasNextByte(int) / boolean java.util.Scanner.hasNextByte())? The above example has overloading in it, which is another problem a human- but mostly computer-readable declarations file would hopefully address.

I've found many sources of human-readable documentation like https://docs.oracle.com/javase/8/docs/api/index.html containing uses of each method, hyperlinks to other places, etc. but never a simple text file or collection of files containing just declarations in any format. If there's no such file(s) don't worry about it, I can try and scrape some annoying HTML files, but if there is it would save a lot of time. Thanks!

Answer 1

The short answer is No.

• There isn't a "header file" containing the class and method signatures for the Java class libraries. The Java tool chain has no need for such a thing. Nor do 3rd-party Java compilers, or compilers for other languages that rely on the Java SE class libraries.

• AFAIK, there isn't a 3rd-party tool that builds such a file or an equivalent database or in-memory data structures.

You could create one though.

• You could chose an existing Java parsing library, and use it to build parse trees for all of the source files in the class library, and emit the information that you need.

• You could potentially create a custom Javadoc "doclet" plugin to emit the information.

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Having said that, I don't understand why you would need such a mapping. Surely, your IDE does this already ... and exposes the information via some internal API. And if this is not for an IDE plugin, what it is for?

You commented:

I'm making a compiler for a JVM-based programming language ....

Ah ... so your compiler should do what other compilers do. Get the information from the ".class" file. You can either load the class using a standard or custom class loader, or you can use a library like asm or bcel or javassist ... which can read a ".class" file without loading it.

^{(I haven't checked, but I think the standard javac compiler uses an internal API to do this.)}

Note that your proposed approaches won't work for interfacing with 3rd-party Java libraries where the source code is not available and/or the javadoc is not scrapable.

Answer 2

What about building it from the source files for the standard library?

The Oracle Java 8 API web pages you referenced was created by Javadoc processing of source files for the Java standard library.

If you use an IDE with a debugger, there is a good chance you already have much of the standard library source code downloaded. After all, if you set a break point, and then follow the program step-by-step with "Step into", you can trace the execution of the program into standard library methods. The source files would be part of the JDK.

However, some parts of the standard library source might not be available, due to licensing restrictions.