The core run-time classes for the java.lang package are:

• Class -- Represents classes and interfaces in a running Java application.
  
  
• Object -- As in J2SE, Object is the base class of all Java objects.
  
  
• Runtime -- Provides a way for a Java application to interact with the run-time environment in which it is running.
  
  
• System -- Provides several static helper methods, as with J2SE.
  
  
• Thread -- Defines a thread of execution for a Java program.
  
  
• Throwable -- The superclass of all errors and exceptions in the Java language.