为什么多个线程能够访问同步块？

Question

运行这个时，我得到IllegalMonitorStateException，因为即使线程试图通知，当它没有锁定对象isEven。这是为什么发生？如果线程锁定了对象，则线程应该只能进入synchronized块。

public class NumPrinter implements Runnable{ 

    public static Boolean isEven = true; 
    private boolean isEvenThread; 
    private int i; 

    public void run() { 
    while(i < 100){ 
    synchronized(isEven){ 
      boolean notPrinting = (isEven^isEvenThread); 
      System.out.println(notPrinting); 
      if(notPrinting) { 
       try { 
        isEven.wait(); 
       } catch (InterruptedException e) { 
        e.printStackTrace(); 
       } 
      }  
      System.out.print(i + ","); 
      i = i+2; 
      isEven = !isEven; 
      isEven.notifyAll(); 
     } 
    } 
    } 

    public NumPrinter(boolean isEvenThread) { 

     this.isEvenThread = isEvenThread; 
     if(isEvenThread) 
      i = 0; 
     else 
      i = 1; 
    } 
} 

public class MultiThreading { 

    public static void main(String[] args) { 

     Thread oddt = new Thread(new NumPrinter(false), "Odd"); 
     Thread event = new Thread(new NumPrinter(true), "Even"); 

     event.start(); 
     oddt.start(); 


    } 
} 

Answer 1

我不是在Java中的专家，但你改写同步令牌这里：

ISEVEN = ISEVEN;

它可能不是唯一的问题，但至少使用另一个同步令牌（这不会被重写）。

Answer 2

您很可能需要对常量对象进行同步/等待/通知。同时声明isEven为易失性。最后，把wait()调用的循环检查循环条件的官方文件recommends：

public class NumPrinter implements Runnable { 
    private static final Object monitor = new Object(); 
    private static volatile boolean isEven = true; 
    private final boolean isEvenThread; 
    private int i; 

    @Override 
    public void run() { 
     while (i < 100) { 
      synchronized (monitor) { 
       while (isEven^isEvenThread) { 
        try { 
         monitor.wait(); 
        } catch (InterruptedException e) { 
         e.printStackTrace(); 
        } 
       } 
       System.out.print(i + ","); 
       i = i + 2; 
       isEven = !isEven; 
       monitor.notifyAll(); 
      } 
     } 
    } 
    ... 
}