Core to the concept of Java modules is understanding the base module. When programming Java applications or porting existing applications programmed with older versions of Java, the base module (java.base) must be used. Every module requires the java.base module because it defines the critical, or foundational, Java platform APIs. 

Here are the contents of the java.base module:

module java.base {
  exports java.io;
  exports java.lang;
  exports java.lang.annotation;
  exports java.lang.invoke;
  exports java.lang.module;
  exports java.lang.ref;
  exports java.lang.reflect;
  exports java.math;
  exports java.net;
  exports java.net.spi;
  exports java.nio;
  exports java.nio.channels;
  exports java.nio.channels.spi;
  exports java.nio.charset;
  exports java.nio.charset.spi;
  exports java.nio.file;
  exports java.nio.file.attribute;
  exports java.nio.file.spi;
  exports java.security;
  exports java.security.aci;
  exports java.security.cert;
  exports java.security.interfaces;
  exports java.security.spec;
  exports java.text;
  exports java.text.spi;
  exports java.time;
  exports java.time.chrono;
  exports java.time.format;
  exports java.time.temporal;
  exports java.time.zone;
  exports java.util;
  exports java.util.concurrent;
  exports java.util.concurrent.atomic;
  exports java.util.concurrent.locks; 
  exports java.util.function;
  exports java.util.jar;
  exports java.util.regex;
  exports java.util.spi;
  exports java.util.stream;
  exports java.util.zip;
  exports java.crypto;
  exports java.crypto.interfaces;
  exports java.crytpo.spec;
  exports java.net;
  exports java.net,ssi;
  exports java.security.auth;
  exports java.security.auth.callbak;
  exports java.security.auth.login;
  exports java.security.auth.spi;
  exports java.security.auth.x500;
  exports java.security.cert;
}

As you can see, the java.base module does not require any modules and it exports numerous packages. It can be useful to have a list of these exports handy so you know what is available to you as you start creating applications using the Java platform.

You will notice that, in the previous section, we did not include the required java.base: the line of code in our declaration of our com.three19.irisScan module. The updated code is provided as follows and now includes the required java.base line of code:

module com.three19.irisScan {
  // modules that com.three19.irisScan depends upon
  requires java.base; // optional inclusion
  requires com.three19.irisCore;
  requires com.three19.irisData;

  // export packages for other modules that are 
  // dependent upon com.three19.irisScan
  exports com.three19.irisScan.biometric;
}

If you do not include the required java.base; the line of code in your module declarations, the Java compiler will automatically include it.