Void

• The Void class have one field called TYPE which holds a reference to the Class object of type void.
• We do not create the instances for this class.

Process

• It is an Abstract class which encapsulates a process , which is an executing program.
• This class is used primarily as a super class for the type of objects created by exec( ) in the Runtime class, or by start( ) in the ProcessBuilder class.

Runtime

• A Runtime class encapsulates the runtime environment.
• We can not instantiate a Runtime object, However we can get the reference to the current Runtime object by calling the static method Runtime.getRuntime().
• By using this reference we can call several methods that control the state and behavior of the Java Virtual Machine.
• Applets and other untrusted code typically cannot call any of the Runtime methods without raising a SecurityException.