Java中关于线程的一个问题。报错

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以下代码中，main函数中，注释部分和非注释部分有什么区别？为何注释部分的运行结果不正确，而非注释部分运行结果正确？

    public class A { public static void main(String[] args) { //Thread xc1=new Thread(new Produce(new Warehouse())); //xc1.start(); //Thread xc2=new Thread(new Sell(new Warehouse())); //xc2.start();

Warehouse wh=new Warehouse(); Produce pd=new Produce(wh); Sell sl=new Sell(wh); Thread xc1=new Thread(pd); xc1.start(); Thread xc2=new Thread(sl); xc2.start(); } } class Warehouse { private char space[]=new char[8]; private int sku=0; public synchronized void sellin(char x) { while(sku==space.length) { try { this.wait(); } catch(Exception e){} } this.notify(); space[sku]=x; ++sku; System.out.println("生产线正在生产第"+sku+"个产品，该产品是"+x); } public synchronized void sellout() { while(sku==0) { try { this.wait(); } catch(Exception e){} } this.notify(); char y=space[sku-1]; --sku; System.out.println("正在消费第"+sku+"个产品，该产品是"+y); } } class Produce implements Runnable { private Warehouse xc=null; Produce(Warehouse x) { this.xc=x; } public void run() { char y; for(int i=0;i<26;i++) { y=(char)('A'+i); xc.sellin(y); } } } class Sell implements Runnable { private Warehouse xc=null; Sell(Warehouse x) { this.xc=x; } public void run() { for(int i=0;i<26;i++) { xc.sellout(); } } }