Organizing Java files and other practicalities - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 135

Yo u can also compile the package files directly, but if the compilation occurs
from the higher directory, you must specify the proper directory name:
C: \ myApps> javac mypack/TestAB.java
(The javac compiler interprets the forward slash “/ „ as a directory separator.
The backslash “ \ „ also works on Windows.) Similarly, the JVM by default looks
for class files in subdirectories as specified by the package names.
Just as a subdirectory can itself contain lower levels of subdirectories,
packages can be nested to lower levels as well. For example, the class def-
inition for TestC shown below includes the directive “package mypack.
extrapack; „ . The TestC.java file must then go into the subdirectory
myApps/mypack/extrapack (or myApps \ mypack \ extrapack onaMS
Windows platform) as shown in Figure 5.1(b).
package mypack.extrapack;
public class TestC {
public boolean flag;
public TestC (boolean b) {
flag = b;
}
}
When the compiler acts on the TestABC class shown below, it uses the
class specification mypack.extrapack.TestC to look in subdirectory
mypack/extrapack/ relative to the directory of TestABC .Itcompiles
TestC.java if there is no class file or if the class file is older than the
TestC.java file.
public class TestABC
{
public static void main (String[] args) {
mypack.TestA testa = new mypack.TestA (4);
mypack.TestB testb = new mypack.TestB (1.3);
mypack.extrapack.TestC testc =
new mypack.extrapack.TestC (true);
if (testc.flag)
System.out.println ( " testa.a =" + testa.a);
else
System.out.println ( " testb.x =" + testb.x);
}
}