Java multi-line layer simultaneous resolution, synchronous code block synchronized

/*multiple line layers manipulating one data at a time leads to data exceeding the synchronization code block synchronized (pair image) {Code to be synchronized}*/classDo7 { Public Static voidMain (string[] args) {Piao P1=NewPiao (); Thread T1=NewThread (p1); Thread T2=NewThread (p1); Thread T3=NewThread (p1); Thread T4=NewThread (p1);    T1.start (); T2.start (); T3.start (); T4.start (); }}classPiaoImplementsrunnable{Private  Static intnum=100; Object obj=NewObject ();//Create a random object for synchronized (image)     Public voidrun () { while(true)        {synchronized(obj)///Synchronous code block    {        if(num>0)        {            Try{Thread.Sleep (10);}Catch(Exception e) {} System.out.println (Thread.CurrentThread (). GetName ()+ "..." +num--); }        Else{        return;}} }    }}

Java multi-line layer simultaneous resolution, synchronous code block synchronized