Java 17 Recipes

 How It Works
Java implements the concept of a classpath. This is a directory search path that you can 
specify system-wide using the CLASSPATH environment variable. You can also specify the 
classpath for a specific invocation of the JVM via the java command’s -classpath option.
When executing Java programs, the JVM finds and loads classes as needed using the 
following search order.
1. The classes that are fundamental to the Java platform and are 
contained in the Java installation directory
2. Any packages or JAR files that are located within the extension 
directory of the JDK
3. Packages, classes, JAR files, and libraries that are loaded 
somewhere on the specified classpath
You may need to access more than one directory or JAR file for an application. This 
could be the case if your dependencies are located in more than one location. To do so, 
simply use the delimiter for your operating system (a ; for Windows and a : for Unix OS) 
as a separator between the locations specified by the CLASSPATH variable. The following 
is an example of specifying multiple JAR files in the CLASSPATH environment variable on 
Unix and Linux systems.
export CLASSPATH=/JAVA_DEV/some-jar.jar:/JAVA_LIB/myjar.jar
Alternatively, you can specify the classpath via a command-line option.
javac –classpath /JAVA_DEV/some-jar.jar:/JAVA_LIB/myjar.jar...
When loading the resources for a Java application, the JVM loads all the classes 
and packages specified in the first location, followed by the second, and so on. This is 
important because the order of loading may make a difference in some instances to 
avoid interfering with one another.
Note JAR files package applications and Java libraries into a distributable 
format. If you have not packaged your application in that manner, you may simply 
specify the directory or directories in which your .class files reside.
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Sometimes you want to include all JAR files within a specified directory. Do that 
by specifying the wildcard character (*) after the directory containing the files. The 
following is an example.
javac –classpath /JAVA_DEV/*:/JAVA_LIB/myjar.jar...
Specifying a wildcard tells the JVM that it should only load JAR files. It does not load 
class files located in a directory specified with the wildcard character. You need to specify 
a separate path entry for the same directory if you also want the class files. The following 
is an example.
javac –classpath /JAVA_DEV/*:/JAVA_DEV
Subdirectories within the classpath are not searched. To load files contained within 
subdirectories, those subdirectories and/or files must be explicitly listed in the classpath. 
However, Java packages that are equivalent to the subdirectory structure are loaded. 
Therefore, any Java classes that reside within a Java package that is equivalent to the 
subdirectory structure are loaded.
Note It is a good idea to organize your code; it is also good to organize where 
you place your code on the computer. A good practice is to place all your Java 
projects within the same directory; it can become your workspace. place all the 
Java libraries that are contained in JAR files into the same directory for easier 
management. You can also use tools like Maven and Gradle to organize your 
project.