How about just hello world?

  public class HelloWorld {
    public static void main(String[] args) {
      // Prints "Hello, World" in the terminal window.
      System.out.println("Hello, World");
    }
  }

This is the full code. This is what I care about on success path:

  System.out.println("Hello, World");
  // Success

Or maybe even just:

  println("Hello, World");

Or maybe, because I forgot what is what in Java:

  java.lang.System - The System class contains several useful
  class fields and methods. It cannot be instantiated.
  |
  |       System.out : java.io.PrintStream - The "standard" output stream.
  |       | 
  |       |    PrintStream::println(String) -> void - Prints a String and then terminate the line.
  v       v    v   
  System.out.println("Hello, World");

This is what I care when I'm looking at the module view:

  HelloWorld (public, class)
    main(String[] args) -> void (public, static, entry point)
    -- Prints "Hello, World" in the terminal window.

This is what I care when I'm looking at error propagation view:

  HelloWorld::main() - entry point
    Program end, return code 0 [default]

Or maybe, given sufficient metadata in the standard library:

  HelloWorld::main() - entry point
    System.out.println("Hello, World")
      -> failed if System.out.checkError() == true
    Program end, return code 0 [default]

Or I want a dependency view:

  HelloWorld
    java.lang.System
    [java.io.PrintStream]

Etc.

Now imagine being able to open the Hello World code, and instantly switch between those views and many others with a single shortcut. Not tooltips above the code, but views that replace code. That is what I'm talking about.

Oh, and views are editable where it makes sense. Even read-only views would improve the development experience a lot, but the magic is in mutable views, so that you don't ever have to touch the full, original form of the source.

EDIT: look at the first vs. third code-block in this comment. People built whole programming languages on the premise that Hello World should look like the third block instead of the first one. That's an extreme case of making a style choice ahead of time, and also a source of endless, pointless debates.