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我有一個包含兩個字符串的數組。我想按字母順序排序。所以這是下面的代碼。null對象引用的java.lang.String.compareToIgnoreCase(java.lang.String)'
ArrayList<String> a = new ArrayList<>();
j = (String) b.get ("user");
a.add (j);
chatroomname.setText (j);
a.add (Fusername);
Log.i ("Size Of A ", String.valueOf (a.size()));
Collections.sort (a, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return o1.compareToIgnoreCase (o2);
}
});
我還在控制檯上記錄了陣列的大小。它顯示了2.哪一個是正確的。所以我不明白爲什麼我得到這個nullpointerexception。
這是我的錯誤日誌:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.buckydroid.anonchat/com.buckydroid.anonchat.ChatRoom}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.compareToIgnoreCase(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6126)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.compareToIgnoreCase(java.lang.String)' on a null object reference
at com.buckydroid.anonchat.ChatRoom$5.compare(ChatRoom.java:244)
at com.buckydroid.anonchat.ChatRoom$5.compare(ChatRoom.java:242)
at java.util.TimSort.countRunAndMakeAscending(TimSort.java:351)
at java.util.TimSort.sort(TimSort.java:216)
at java.util.Arrays.sort(Arrays.java:1523)
at java.util.Collections.sort(Collections.java:238)
at com.buckydroid.anonchat.ChatRoom.onCreate(ChatRoom.java:241)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6126)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
感謝名單!
我的猜測是列表中的一個或多個值爲空。我建議你通過調試器中的代碼來查看哪一個以及爲什麼。 –
打印出列表'a',看看裏面有什麼... – nafas
可能有[NullPointerException異常,以及如何解決它?]重複(http://stackoverflow.com/questions/218384/what-is- a-nullpointerexception-and-how-do-i-fix-it) –