09

• Concurrency


  The property of executing multiple threads and processes simultaneously
• Thread


  The smallest unit of execution that can be scheduled by the operating system
• Process


  A group of associated threads executed in the same shared environment
• A single-threaded process contains exactly one thread, whereas a multithreaded process supports more than one thread
• In a shared environment, threads in the same process share the same memory space and can communicate directly with one another
• Thread scheduler


  Determines which threads should be currently executing
• Context switch


  The process of storing a thread's current state and later restoring the state of the thread to continue execution
• When a Java application starts, its main() method is executed by the main thread – a special thread that is created by the Java VM to run your application
• Creating a thread in Java


  1. Extend the Thread class and override the run() method

  2. Implement the Runnable interface
• Extending the Thread class

  • public class ThreadDemo extends Thread { ... }
• Implementing the Runnable interface

  • public class ThreadDemo implements Runnable { ... }
• Thread methods


  • start
  • run
  • setName
  • getName
  • setPriority
  • getPriority
  • isAlive
  • join
  • sleep
• Thread priority


  A numeric value associated with a thread that is taken into consideration by the thread scheduler when determining which threads should currently be executing
• The value of the priority level must be within the range MIN_PRIORITY and MAX_PRIORITY. These values are 1 and 10, respectively. To return a thread to default priority, specify NORM_PRIORITY, which is 5
• Using setName(), getName(), and setPriority()


  • public class ThreadDemo extends Thread { ... }
• Using sleep(), join(), and isAlive()

  • public class ThreadDemo extends Thread { ... }
• A thread with higher priority does not necessarily mean that it will run faster or more often than others; it only has greater potential access to the CPU
• The Thread.currentThread() method returns a reference to the Thread instance executing currentThread()