Fernflower is open-source software available at github.com/JetBrains/fe....

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Simply run `fernflower Calculator.class <output-directory>`,
and Fernflower will analyze the .class file and recreate a .java file.

There's also the `javap` program, which comes with the JDK.
It can display classes, fields, and method signatures nicely,
but if you want to see the contents of method bodies, you need to use the `-c` flag.
Its output is hard to read and understand.

Fernflower to the rescue!

Let's say you have a compiled calculator program in a Calculator.class file.

Java bytecode in .class files is stored in a special binary format,
which is unreadable with a normal `cat` program.

Fernflower is a Java bytecode decompiler.
It can recreate a .java file from a .class file (which contains compiled Java bytecode).
This is useful in the context of reverse engineering, when you need to see the source code of a library but you only have access to its JAR.