我有一个包含两个字符串的数组。我想按字母顺序对其进行排序。所以这是下面的代码。
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);
}
});
我还在控制台上记录了数组的大小。它显示 2。哪个是正确的。所以我不明白为什么我会得到这个空指针异常。
这是我的错误日志:
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)
谢谢!!!
最佳答案
如果异常来自您粘贴的代码,请不仅检查a
数组的大小,还要检查其内容。它可能存储 2 个值,但它们可能为 null
。
关于空对象引用上的 java.lang.String.compareToIgnoreCase(java.lang.String)',我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/42505211/