Java source to .class mapping

1.green-Yellow.java

// Here's a .java file, named 'Yellow.java'

// Inside a package (and directory) named 'green'
package green;

// Here's a class named 'Blue'
class Blue {

  // Here's a method named 'foo' inside 'Blue'
  void foo() {
  
    // here's an anonymous class declaration, extending java.lang.Runnable
    new Runnable() {
    
      // Here's a method named 'run' inside this anonymous class
      public void run() {
      }
    };
  }
}

2.compile.sh

# our source file is in a package (directory)

% find
.
./green
./green/Yellow.java

# compile, not including debug information (it's a release!)
% mkdir -p output && javac -d output -g:none green/Yellow.java

# we've written some .class files...
% find
.
./green
./green/Yellow.java
./output
./output/green
./output/green/Blue$1.class
./output/green/Blue.class

# put them in the jar
% jar cf prod.jar -C output .

# done!
% jar tf prod.jar
META-INF/
META-INF/MANIFEST.MF
green/
green/Blue$1.class
green/Blue.class

3.wat.md

green/Blue.class contains green.Blue:

% javap -c output/green/Blue.class | head -n1
class green.Blue {

green/Blue$1.class contains green.Blue$1:

% javap -c 'output/green/Blue$1.class' | head -n1 
class green.Blue$1 implements java.lang.Runnable {

The path is irrelevant, it still knows what it is called:

% cp output/green/Blue.class Pink.class
% javap -c Pink.class
class green.Blue {