这个问题在这里已经有答案了：

什么是nullpointerexception，如何修复它(12个答案）
上个月关门了。
我想在firebase中存储的配置文件页上显示数据，但当我尝试只显示数字文本，运行应用程序，然后转到用户的配置文件页时，会出现如下错误：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.drheartbeatmonitor, PID: 3415
java.lang.RuntimeException: Unable to start activity 
ComponentInfo{com.example.drheartbeatmonitor/com.example.drheartbeatmonitor.Profile}: 
java.lang.NullPointerException: Attempt to invoke virtual method 'void 
android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
    at 
android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:223)
    at android.app.ActivityThread.main(ActivityThread.java:7656)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void 
android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.example.drheartbeatmonitor.Profile.onCreate(Profile.java:67)
    at android.app.Activity.performCreate(Activity.java:8000)
    at android.app.Activity.performCreate(Activity.java:7984)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
    at 
android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:223) 
    at android.app.ActivityThread.main(ActivityThread.java:7656) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 

这是我的代码：1.登录页面：

String ID_Device = snapshot.child(Username).child("ID_Device").getValue().toString();
String HealthInsure = snapshot.child(Username).child("Health Insure").getValue().toString();
intent.putExtra("ID_Device", ID_Device);
intent.putExtra("Health Insure", HealthInsure);

2.个人资料页

String ID_Device = Patient.ID_Device;
String HealthInsure = Patient.HealthInsure;
health_insure.setText(HealthInsure);
ID_Dev.setText(ID_Device);