java Integer not being operated lock it ?

public class TestVolitile extends Thread {
  
  	TestVolitile(int id) {
  		this.setName("thread :" + id);
  	}
  
  	public static Integer n = new Integer(0);
  	public static byte[] lock=new byte[0];
  
  	public void run() {
  		synchronized (n) {
  //			System.err.println(getName() + "  n " + n);
  			for (int i = 0; i < 3; i++) {
  				n++;
  				try {
  					sleep(1);
  				} catch (InterruptedException e) {
  				} // 为了使运行结果更随机，延迟3毫秒
  			}
  //			System.err.println(getName() + "  end " + n);
  		}
  	}
  	
  	static void runTest() throws InterruptedException{
  		Thread threads[] = new Thread[1000];
  		for (int i = 0; i < threads.length; i++)
  			// 建立100个线程
  			threads[i] = new TestVolitile(i);
  		for (int i = 0; i < threads.length; i++)
  			// 运行刚才建立的100个线程
  			threads[i].start();
  		for (int i = 0; i < threads.length; i++)
  			// 100个线程都执行完后继续
  			threads[i].join();
  		System.out.println(" n= " + TestVolitile.n);
  		TestVolitile.n=0;
  	}
  
  	public static void main(String[] args) throws Exception {
  		for (int i = 0; i < 50; i++) {
  			runTest();
  		}
  	}
  }

n
Why not lock , for a lock on it too ?
------ Solution ---------------------------------------- ----
you use public static byte [] lock = new byte [0] like ? Why ? Because you are in the code , did not modify this variable , public static byte [] lock = new byte [0] and I wrote above
private Object obj = new Object ();
synchronized (obj)
and
synchronized (this)
no distinction , are objects of the built-in lock. Sync it are thread safe. Your
public static Integer n = new Integer (0);
by you for n + +; operation modified.

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Integer is final, + + operator will regenerate an object or value.
n = n +1; like to try it ?
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Well, I was wrong. . n + + and n = n +1 the same effect. .
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really do not understand what you write What is ? Your program want to do ?
launched 50,000 threads, which is to be doing it ? Did not understand
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is to test multithreaded lock , synchronized (n) {......}

began to use public static Integer n = new Integer (0); this object when the lock and found that does not work, then replace public static ; byte [] lock = new byte [0]; object , like, do not know which is operated in the thread object n, can not be used as a lock object ?
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  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.atomic.AtomicInteger;
  
  public class Test01 implements Runnable {
  	private String name;
  	private TestThread t;
  	private AtomicInteger count = new AtomicInteger();
  
  	public Test01(String name, TestThread t) {
  		super();
  		this.name = name;
  		this.t = t;
  	}
  
  	@Override
  	public void run() {
  		Thread.currentThread().setName(name);
  		while (true) {
  			t.showCount();
  			if (10 > count.getAndIncrement()) {
  				break;
  			}
  		}
  	}
  
  	/**
  	 * @param args
  	 */
  	public static void main(String[] args) {
  		ExecutorService exec = Executors.newCachedThreadPool();
  		TestThread t = new TestThread();
  		for (int i = 0; i < Runtime.getRuntime().availableProcessors() * 4; i++) {
  			exec.execute(new Test01("thread-" + i, t));
  		}
  		exec.shutdown();
  
  	}
  }
  
  class TestThread {
  	private Object obj = new Object();
  	private int count;
  
  	public void showCount() {
  		synchronized (obj) {
  		//synchronized (this) {//这里可以用obj，可以用this
  			try {
  				System.out.println(Thread.currentThread().getName()
  						+ " before --> " + count);
  				synchronized (obj) {
  					count++;
  				}
  				System.out.println(Thread.currentThread().getName()
  						+ " after --> " + count);
  			} catch (Exception e) {
  				e.printStackTrace();
  			}
  		}
  	}
  }
  

look at this code .
I use here the object's internal lock to ensure thread safety. Can I use my above

  private Object obj = new Object();
  synchronized (obj)
  

You can also use

  synchronized (this)
  

effect of the two is the same. Of course, you can also use the display

private Lock lock = new ReentrantLock();

to lock and unlock .
you use public static Integer n = new Integer (0); when, in the back of the implementation of n + +; operation. You have to understand , n + + This operation , in fact, is the production of a new n, then n is assigned to . Your lock " invariance " has long ceased to exist. You may want to print out n, not long ago the beginning of the n it. Go and see "Java concurrent programming combat " it.
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6 Floor positive solution, is reading that book , ha ha , thank you