Java 中 synchronized的用法详解(四种用法)

   public synchronized void synMethod() {
    //方法体
   }

   public int synMethod(int a1){
    synchronized(a1) {
     //一次只能有一个线程进入
    }
   }

 public class MyThread implements Runnable {
  public static void main(String args[]) {
  MyThread mt = new MyThread();
  Thread t1 = new Thread(mt, "t1");
  Thread t2 = new Thread(mt, "t2");
  Thread t3 = new Thread(mt, "t3");
  Thread t4 = new Thread(mt, "t4");
  Thread t5 = new Thread(mt, "t5");
  Thread t6 = new Thread(mt, "t6");
  t1.start();
  t2.start();
  t3.start();
  t4.start();
  t5.start();
  t6.start();
 }
 public void run() {
  synchronized (this) {
   System.out.println(Thread.currentThread().getName());
  }
 }
} 

class FineGrainLock {
  MyMemberClass x, y;
  Object xlock = new Object(), ylock = new Object();
  public void foo() {
   synchronized(xlock) {
     //access x here
   }
   //do something here - but don't use shared resources
   synchronized(ylock) {
     //access y here
   }
  }
  public void bar() {
   synchronized(this) {
     //access both x and y here
   }
   //do something here - but don't use shared resources
  }
 }

class ArrayWithLockOrder{
 private static long num_locks = 0;
 private long lock_order;
 private int[] arr;
 public ArrayWithLockOrder(int[] a)
 {
  arr = a;
  synchronized(ArrayWithLockOrder.class) {//-----这里
   num_locks++;       // 锁数加 1。
   lock_order = num_locks; // 为此对象实例设置唯一的 lock_order。
  }
 }
 public long lockOrder()
 {
  return lock_order;
 }
 public int[] array()
 {
  return arr;
 }
 }
 class SomeClass implements Runnable
 {
 public int sumArrays(ArrayWithLockOrder a1,
            ArrayWithLockOrder a2)
 {
  int value = 0;
  ArrayWithLockOrder first = a1;    // 保留数组引用的一个
  ArrayWithLockOrder last = a2;    // 本地副本。
  int size = a1.array().length;
  if (size == a2.array().length)
  {
   if (a1.lockOrder() > a2.lockOrder()) // 确定并设置对象的锁定
   {                   // 顺序。
    first = a2;
    last = a1;
   }
   synchronized(first) {       // 按正确的顺序锁定对象。
    synchronized(last) {
     int[] arr1 = a1.array();
     int[] arr2 = a2.array();
     for (int i=0; i<size; i++)
      value += arr1[i] + arr2[i];
    }
   }
  }
  return value;
 }
 public void run() {
  //
 }
 }

public synchronized void method(){
  // 
}

public void method()  {  
  synchronized (this)   
  {  
    //..  
  }  
} 

public void method() { 
synchronized (this) 
{ 
//.. 
} 
} 

 private byte[] lock = new byte[0]; 
  Public void method(){  
      synchronized(lock) 
      { 
        // 
      }
  }  

Class Foo  
{  
  public synchronized static void method1()  

  {  
    //.  
  }  
  public void method2()  
  {  
    synchronized(Foo.class)  
    //
  }  
}