正确的判断如下:
String str = null;
if(str != null){//TODO}
易报错的写法:
String str = null;
if(!str.isEmpty()){}
//这样判断逻辑上没问题,只是在str不为空时可以,一旦为null,就会报错,
报错信息如下 :
2019-01-03 14:52:16.456 2837-2837/net.sinorock.ajj E/AndroidRuntime: FATAL EXCEPTION: main
Process: net.sinorock.ajj, PID: 2837
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference
at net.sinorock.ajj.ui.examine.zlqxzg.chuzhi.ZlxqzgczActivity.setDate(ZczActivity.java:166)
at net.sinorock.ajj.ui.examine.zlqxzg.chuzhi.ZlxqzgczActivity$1.onChanged(ZczActivity.java:63)
at net.sinorock.ajj.ui.examine.zlqxzg.chuzhi.ZlxqzgczActivity$1.onChanged(ZczActivity.java:51)
at android.arch.lifecycle.LiveData.considerNotify(LiveData.java:109)
at android.arch.lifecycle.LiveData.dispatchingValue(LiveData.java:126)
at android.arch.lifecycle.LiveData.setValue(LiveData.java:282)
at android.arch.lifecycle.LiveData$1.run(LiveData.java:87)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:171)
at android.app.ActivityThread.main(ActivityThread.java:6656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)