Bonjour mes amis,

Lorsque je teste l'application Android sur mon téléphone Samsung S6 la version Android 7.0, toujours il affiche ce message "application s'est arrêté". Je ne sais pas comment résoudre ce problème?

Voici le problème :
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01-04 12:00:50.992 13186-13186/? E/AndroidRuntime: FATAL EXCEPTION: main
                                                   Process: yassine.com.calculator, PID: 13186
                                                   java.lang.RuntimeException: Unable to start activity ComponentInfo{yassine.com.calculator/yassine.com.calculator.MainActivity}: 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:2927)
                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2988)
                                                       at android.app.ActivityThread.-wrap14(ActivityThread.java)
                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631)
                                                       at android.os.Handler.dispatchMessage(Handler.java:102)
                                                       at android.os.Looper.loop(Looper.java:154)
                                                       at android.app.ActivityThread.main(ActivityThread.java:6682)
                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)
                                                    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                                                       at yassine.com.calculator.MainActivity.onCreate(MainActivity.java:22)
                                                       at android.app.Activity.performCreate(Activity.java:6942)
                                                       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126)
                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2880)
                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2988)*
                                                       at android.app.ActivityThread.-wrap14(ActivityThread.java)*
                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631)*
                                                       at android.os.Handler.dispatchMessage(Handler.java:102)*
                                                       at android.os.Looper.loop(Looper.java:154)*
                                                       at android.app.ActivityThread.main(ActivityThread.java:6682)*
                                                       at java.lang.reflect.Method.invoke(Native Method)*
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)*
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)*
01-04 12:00:50.997 13186-13186/? I/Process: Sending signal. PID: 13186 SIG: 9