什麼是java.lang.ClassCastException：java.util.ArrayList

Question

我的代碼拋出java.lang.ClassCastException異常錯誤，爲什麼這個錯誤會得到？我正在使用com.android.internal.telephony API。即你可以找到類的，我在這裏使用Call.java <http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/1.5_r4/com/android/internal/telephony/Call.java>，CallManger.java <http://hi-android.info/src/com/android/internal/telephony/CallManager.java.html>我創建Call.java的Subclaas這樣的：

public class MyCall extends Call{ 

     CallManager cm = CallManager.getInstance(); 
     Phone.State state; 
     Connection c; 
     Phone mDefaultPhone; 
     private final ArrayList<Connection> emptyConnections = new ArrayList<Connection>();  
     MyCall ringingCall;  

     @Override 
     public List<Connection> getConnections() {   
      state = cm.getState();  
      ringingCall = (MyCall) cm.getRingingCalls(); 
      System.out.println("**inside getConnections="+ringingCall);  
      if (ringingCall != null && !ringingCall.isIdle()) { 
       System.out.println("**call is not null***"); 
       return ((MyCall) ringingCall).getConnections(); 
      }  
      else 
      { 
       System.out.println("**list is null***"); 
       return emptyConnections; 
      }  
     } 

     @Override 
     public Phone getPhone() { 
      // TODO Auto-generated method stub 
      return null; 
     } 

     @Override 
     public void hangup() throws CallStateException { 
      // TODO Auto-generated method stub 

     } 

     @Override 
     public boolean isMultiparty() { 
      // TODO Auto-generated method stub 
      return false; 
     } 

     public Connection 
     getEarliestConnection() { 
      System.out.println("inside EarliestConnection"); 
      List l; 
      long time = Long.MAX_VALUE; 
      Connection c; 
      Connection earliest = null; 

      l = getConnections(); 

      if (l == null) { 
       return null; 
      }else if (l.size() == 0) 
      { 
       return null; 
      } 

      System.out.println("value of connection is=="+l); 
      for (int i = 0, s = l.size() ; i < s ; i++) { 
       c = (Connection) l.get(i); 
       long t; 

       t = c.getCreateTime(); 

       if (t < time) { 
        earliest = c; 
        time = t; 
       } 
      } 

     return earliest; 
    } 
} 

我在我自己的類名爲CallManger.java這樣

CallManager cm = CallManager.getInstance(); 

我的另一個類是CallUpdate，就應該給我一個OutgoingCall狀態（即對方電話佔線，關機，不可達的等）的代碼是這樣的：

public class CallUpdate { 

    Call myCall = new MyCall(); 
    Connection myConn = new MyConnection(); 
    CallManager cm = CallManager.getInstance(); 

     public Object getCallFailedString(){ 

      myConn = myCall.getEarliestConnection(); 
      System.out.println("myConn is ******"+myConn); 
      System.out.println("myCall is ******"+myCall); 

      if(myConn == null){ 
       System.out.println("myConn is null ******"); 
       return null; 
      }     
      else 
      { 
       Connection.DisconnectCause cause = myConn.getDisconnectCause();      
       System.out.println("myconn is not null ******"+cause); 


       switch(cause){ 

       case BUSY : 
        System.out.println("inside busy"); 
       break; 

       case NUMBER_UNREACHABLE : 
        System.out.println("inside un-reachable"); 
       break; 

       case POWER_OFF : 
        System.out.println("inside power off"); 
       break; 
       } 
     } 
    return myConn; 
} 

我在BroadCastReceiver（）中調用了這個類。但我得到的連接是空的。我的代碼沒有進入其他部分。所以，我在的MyCall類的getConnection方法這樣增加了一些代碼：

public List<Connection> getConnections() {  


    state = cm.getState();  
    ringingCall = (MyCall) cm.getRingingCalls(); 
     System.out.println("**inside getConnections="+ringingCall);   
      if (ringingCall != null && !ringingCall.isIdle()) { 
      System.out.println("**call is not null***"); 
      return ((MyCall) ringingCall).getConnections(); 
     }  
     else 
     { 
      System.out.println("**list is null***"); 
      return emptyConnections; 
     } 
    } 

但我正在逐漸java.lang.ClassCastException：上線： ringingCall = (MyCall) cm.getRingingCalls(); 而且還l = getConnection(); 如何解決這個問題？ Thx提前。

Answer 1

更改您的代碼如下

List<MyCall> ringingCall = cm.getRingingCalls();

我相信你cm.getRingingCalls();返回ArrayList的Call/MyCall

Answer 2

getRingingCalls返回Call對象的List<Call>即列表。您正試圖將其投射到單個MyCall而不是List，因此您將獲得ClassCastException。

您需要更正你的類型的List：

List<MyCall> ringingCall; 
ringingCall = cm.getRingingCalls(); 

，或者使用的第一個元素在列表中：

MyCall ringingCall; 
if(!cm.getRingingCalls().isEmpty()){ 
    ringingCall = cm.getRingingCalls().get(0); 
}