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Thread Back

  • Thread(線程)指一個程序中的執行片段,且擁有併發執行的特性.
  • 線程間通信可通過共享全局變量來實現


  • 同步: 指事件處理存在一定的協作順序,而這個順序的改變將會導致結果的差錯. (Semaphore)
  • 互斥: 指多個進程將要讀取同一區域(關鍵區)的數據時,將只能允許一個進程進入. (Mutex)

Ways to create a thread

  • Inherit from the calss Thread (java.lang.Thread)
class MyThread extends Thread

    public void run()
        //What you want this thread to do
  • implements Runnable interface

    • with this

      class MyThread implements Runnable
        Thread t;
            t = new Thread(this);
        public void run() 
            //What you want this thread to do
    • with unnamed inner class

      Thread MyThread = new Thread(
      new Runnable()
        public void run()
            //What you want this thread to do

some methods of Threads

  • join()
t.join();    //Wait for this thread to die
  • yield()
t.yield();    //Causes the currently executing thread object to temporarily pause 
        //and allow other threads to execute.
  • setPriority(int newPriority)
t.setPriorty(MAX_PRIORITY);    //Changes the priority of this thread to a max one

/*    java.lang.Thread
*    public static final int    MAX_PRIORITY    10
*    public static final int    MIN_PRIORITY    1
*    public static final int    NORM_PRIORITY    5

When sharing same datas

/* do with shared datas */
public synchronized void transfer()
    //synchronized label ensures that this thread won't be schedule out when running this method.

States of a Thread

  1. Process blocks for input
  2. Scheduler picks another process
  3. Scheduler picks this process
  4. Input becomes available
  • Blocked State
Thread.sleep(100);    //Blocked State (do not release lock)


wait();            //Blocked State (release lock and need other threads to call notify() or notifyall())
  • Run State
Thread t = new MyThread()    //Initialize
t.start();    //Run State
            //Ready State: Waiting CPU to call it
  • Ready State
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