synchronized的使用及死鎖現象

本程序轉自尚學堂馬老師課上代碼

synchronized的使用：

synchronized執行這個方法時，當前對象被鎖定

public class TestSync implements Runnable {
  Timer timer = new Timer();
  public static void main(String[] args) {
    TestSync test = new TestSync();
    Thread t1 = new Thread(test);
    Thread t2 = new Thread(test);
    t1.setName("t1");
    t2.setName("t2");
    t1.start();
    t2.start();
  }
  public void run(){
    timer.add(Thread.currentThread().getName());
  }
}

class Timer{
  private static int num = 0;
  //synchronized執行這個方法時，當前對象被鎖定
  public synchronized void add(String name){
   num ++;
      try {Thread.sleep(1);}
   catch (InterruptedException e) {}
   System.out.println(name+", 你是第"+num+"個使用timer的線程");  
  }
}

死鎖現象模擬程序：

public class TestDeadLock implements Runnable {
 public int flag = 1;
 static Object o1 = new Object(), o2 = new Object();
 public void run() {
        System.out.println("flag=" + flag);
        //鎖住o1，同時鎖住了o2
  if(flag == 1) {
   //synchronized 鎖方法
   synchronized(o1) {
    try {
     Thread.sleep(500);
    } catch (Exception e) {
     e.printStackTrace();
    }
    synchronized(o2) {
     System.out.println("1"); 
    }
   }
  }
  //鎖住o2，同時鎖住了o1
  if(flag == 0) {
   synchronized(o2) {
    try {
     Thread.sleep(500);
    } catch (Exception e) {
     e.printStackTrace();
    }
    synchronized(o1) {
     System.out.println("0");
    }
   }
  }
 } 
 
 public static void main(String[] args) {
  TestDeadLock td1 = new TestDeadLock();
  TestDeadLock td2 = new TestDeadLock();
  td1.flag = 1;
  td2.flag = 0;
  Thread t1 = new Thread(td1);
  Thread t2 = new Thread(td2);
  t1.start();
  t2.start();
  
 }
}