有 wait就必须要有synchronized，不然会报错吗？？?报错

这个代码没有 synchronized也没报错啊，怎吗做到滴？？？

packagetank;
importjava.awt.BorderLayout;
importjava.awt.FlowLayout;
importjava.awt.event.ActionEvent;
importjava.awt.event.ActionListener;
 
importjavax.swing.JButton;
importjavax.swing.JFrame;
importjavax.swing.JLabel;
importjavax.swing.JPanel;
 
publicclassTestAppextendsJFrameimplementsActionListener,Runnable{
  privateTestThreadthread=null;
 
  publicTestApp(){
 
    JPanelbuttons=newJPanel();
    FlowLayoutlayout=newFlowLayout(FlowLayout.CENTER);
    buttons.setLayout(layout);
    add(buttons,BorderLayout.NORTH);
 
    JButtonbtn=newJButton("pause");
    btn.addActionListener(this);
    buttons.add(btn);
 
    JLabellabel=newJLabel();
    add(label,BorderLayout.CENTER);
 
    setSize(800,600);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
    thread=newTestThread(label);
    thread.start();
  }
 
  publicstaticvoidmain(String[]args){
    newTestApp();
  }
 
  publicvoidactionPerformed(ActionEvente){
    JButtonbtn=(JButton)e.getSource();
    if("pause".equals(btn.getText())){
      btn.setText("start");
      thread.callWait();
    }else{
      btn.setText("pause");
      thread.call();
    }
  }
 
  publicvoidrun(){}
}
 
classTestThreadextendsThread{
  privatebooleanisWait=false;
  privateJLabellabe=null;
 
  publicTestThread(JLabellabe){
    this.labe=labe;
  }
 
  publicvoidrun(){
    intindex=0;
    while(true){
      try{
        if(isWait){
          wait();
        }
        labe.setText(""+(++index));
        sleep(500);
      }catch(Exceptione){
 
      }
    }
  }
 
  publicsynchronizedvoidcallWait(){
    isWait=true;
  }
 
  publicsynchronizedvoidcall(){
    isWait=false;
    notify();
  }
}

你把异常吃掉了