Java 标记“”上的语法错误；扩展；在服务中实现PhoneStateListener时引发

我试图在服务中实现电话状态侦听器，但收到错误：

Syntax error on token "extends", throws expected

但当我将

扩展
更改为
抛出
时，我会收到3个新错误，说明：

EndCallListener cannot be resolved to a type 
EndCallListener cannot be resolved to a type
No exception of type PhoneStateListener can be thrown; an exception type must be a subclass of Throwable

有什么建议吗

阿曼尼·斯旺

public void onCreate() extends PhoneStateListener {
  EndCallListener callListener = new EndCallListener();
  TelephonyManager mTM = (TelephonyManager)this.getSystemService(Context.TELEPHONY_SERVICE);
   mTM.listen(callListener, PhoneStateListener.LISTEN_CALL_STATE);
 }

 public void onCallStateChanged(int state, String incomingNumber) {
  if(TelephonyManager.CALL_STATE_OFFHOOK == state) {
    // set number of calls to 1 in SharedPreferences                    
   SharedPreferences pref = getApplicationContext()
     .getSharedPreferences("DataCountService", 0);
   Editor editor = pref.edit();
    editor.putString("calls", "1");
   editor.commit();
  }

如果onCreate实际上是一个方法，正如返回类型“void”和名称后的括号所示，则不能在那里使用extends。只有类可以从其他类继承

public class ClassName extends ParentClassName { //class code }

在这里你可以找到关于继承的神谕