[Java for Android App Development] krikor1:
I do that, i get my first app has to be stopped

09-19 18:47:05.798: E/AndroidRuntime(29848): FATAL EXCEPTION: main
09-19 18:47:05.798: E/AndroidRuntime(29848): java.lang.IllegalStateException: Could not execute method of the activity
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.view.View$1.onClick(View.java:3633)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.view.View.performClick(View.java:4240)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.view.View$PerformClick.run(View.java:17721)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.os.Handler.handleCallback(Handler.java:730)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.os.Handler.dispatchMessage(Handler.java:92)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.os.Looper.loop(Looper.java:137)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.app.ActivityThread.main(ActivityThread.java:5103)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at dalvik.system.NativeStart.main(Native Method)
09-19 18:47:05.798: E/AndroidRuntime(29848): Caused by: java.lang.reflect.InvocationTargetException
09-19 18:47:05.798: E/AndroidRuntime(29848):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.view.View$1.onClick(View.java:3628)
09-19 18:47:05.798: E/AndroidRuntime(29848):	... 11 more
09-19 18:47:05.798: E/AndroidRuntime(29848): Caused by: java.lang.NullPointerException: println needs a message
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.util.Log.println_native(Native Method)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at android.util.Log.d(Log.java:138)
09-19 18:47:05.798: E/AndroidRuntime(29848):	at com.example.myfirstapp.MainActivity.sendMessage(MainActivity.java:82)
09-19 18:47:05.798: E/AndroidRuntime(29848):	... 14 more
09-19 18:47:30.955: E/AndroidRuntime(30168): FATAL EXCEPTION: main
09-19 18:47:30.955: E/AndroidRuntime(30168): java.lang.IllegalStateException: Could not execute method of the activity
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.view.View$1.onClick(View.java:3633)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.view.View.performClick(View.java:4240)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.view.View$PerformClick.run(View.java:17721)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.os.Handler.handleCallback(Handler.java:730)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.os.Handler.dispatchMessage(Handler.java:92)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.os.Looper.loop(Looper.java:137)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.app.ActivityThread.main(ActivityThread.java:5103)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at dalvik.system.NativeStart.main(Native Method)
09-19 18:47:30.955: E/AndroidRuntime(30168): Caused by: java.lang.reflect.InvocationTargetException
09-19 18:47:30.955: E/AndroidRuntime(30168):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.view.View$1.onClick(View.java:3628)
09-19 18:47:30.955: E/AndroidRuntime(30168):	... 11 more
09-19 18:47:30.955: E/AndroidRuntime(30168): Caused by: java.lang.NullPointerException: println needs a message
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.util.Log.println_native(Native Method)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at android.util.Log.d(Log.java:138)
09-19 18:47:30.955: E/AndroidRuntime(30168):	at com.example.myfirstapp.MainActivity.sendMessage(MainActivity.java:82)
09-19 18:47:30.955: E/AndroidRuntime(30168):	... 14 more
09-19 18:49:17.259: E/AndroidRuntime(30750): FATAL EXCEPTION: main
09-19 18:49:17.259: E/AndroidRuntime(30750): java.lang.IllegalStateException: Could not execute method of the activity
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.view.View$1.onClick(View.java:3633)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.view.View.performClick(View.java:4240)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.view.View$PerformClick.run(View.java:17721)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.os.Handler.handleCallback(Handler.java:730)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.os.Handler.dispatchMessage(Handler.java:92)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.os.Looper.loop(Looper.java:137)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.app.ActivityThread.main(ActivityThread.java:5103)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at dalvik.system.NativeStart.main(Native Method)
09-19 18:49:17.259: E/AndroidRuntime(30750): Caused by: java.lang.reflect.InvocationTargetException
09-19 18:49:17.259: E/AndroidRuntime(30750):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.view.View$1.onClick(View.java:3628)
09-19 18:49:17.259: E/AndroidRuntime(30750):	... 11 more
09-19 18:49:17.259: E/AndroidRuntime(30750): Caused by: java.lang.NullPointerException: println needs a message
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.util.Log.println_native(Native Method)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at android.util.Log.e(Log.java:231)
09-19 18:49:17.259: E/AndroidRuntime(30750):	at com.example.myfirstapp.MainActivity.sendMessage(MainActivity.java:82)
09-19 18:49:17.259: E/AndroidRuntime(30750):	... 14 more
09-19 18:50:39.907: E/AndroidRuntime(31052): FATAL EXCEPTION: main
09-19 18:50:39.907: E/AndroidRuntime(31052): java.lang.IllegalStateException: Could not execute method of the activity
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.view.View$1.onClick(View.java:3633)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.view.View.performClick(View.java:4240)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.view.View$PerformClick.run(View.java:17721)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.os.Handler.handleCallback(Handler.java:730)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.os.Handler.dispatchMessage(Handler.java:92)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.os.Looper.loop(Looper.java:137)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.app.ActivityThread.main(ActivityThread.java:5103)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at dalvik.system.NativeStart.main(Native Method)
09-19 18:50:39.907: E/AndroidRuntime(31052): Caused by: java.lang.reflect.InvocationTargetException
09-19 18:50:39.907: E/AndroidRuntime(31052):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.view.View$1.onClick(View.java:3628)
09-19 18:50:39.907: E/AndroidRuntime(31052):	... 11 more
09-19 18:50:39.907: E/AndroidRuntime(31052): Caused by: java.lang.NullPointerException: println needs a message
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.util.Log.println_native(Native Method)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at android.util.Log.println(Log.java:332)
09-19 18:50:39.907: E/AndroidRuntime(31052):	at com.example.myfirstapp.MainActivity.sendMessage(MainActivity.java:82)
09-19 18:50:39.907: E/AndroidRuntime(31052):	... 14 more
09-19 18:51:10.640: E/AndroidRuntime(31288): FATAL EXCEPTION: main
09-19 18:51:10.640: E/AndroidRuntime(31288): java.lang.IllegalStateException: Could not execute method of the activity
09-19 18:51:10.640: E/AndroidRuntime(31288):	at android.view.View$1.onClick(View.java:3633)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at android.view.View.performClick(View.java:4240)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at android.view.View$PerformClick.run(View.java:17721)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at android.os.Handler.handleCallback(Handler.java:730)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at android.os.Handler.dispatchMessage(Handler.java:92)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at android.os.Looper.loop(Looper.java:137)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at android.app.ActivityThread.main(ActivityThread.java:5103)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at dalvik.system.NativeStart.main(Native Method)
09-19 18:51:10.640: E/AndroidRuntime(31288): Caused by: java.lang.reflect.InvocationTargetException
09-19 18:51:10.640: E/AndroidRuntime(31288):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:51:10.640: E/AndroidRuntime(31288):	at android.view.View$1.onClick(View.java:3628)
09-19 18:51:10.640: E/AndroidRuntime(31288):	... 11 more
09-19 18:51:10.640: E/AndroidRuntime(31288): Caused by: java.lang.NullPointerException
09-19 18:51:10.640: E/AndroidRuntime(31288):	at com.example.myfirstapp.MainActivity.sendMessage(MainActivity.java:82)
09-19 18:51:10.640: E/AndroidRuntime(31288):	... 14 more
09-19 18:54:51.165: E/AndroidRuntime(31543): FATAL EXCEPTION: main
09-19 18:54:51.165: E/AndroidRuntime(31543): java.lang.IllegalStateException: Could not execute method of the activity
09-19 18:54:51.165: E/AndroidRuntime(31543):	at android.view.View$1.onClick(View.java:3633)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at android.view.View.performClick(View.java:4240)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at android.view.View$PerformClick.run(View.java:17721)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at android.os.Handler.handleCallback(Handler.java:730)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at android.os.Handler.dispatchMessage(Handler.java:92)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at android.os.Looper.loop(Looper.java:137)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at android.app.ActivityThread.main(ActivityThread.java:5103)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at dalvik.system.NativeStart.main(Native Method)
09-19 18:54:51.165: E/AndroidRuntime(31543): Caused by: java.lang.reflect.InvocationTargetException
09-19 18:54:51.165: E/AndroidRuntime(31543):	at java.lang.reflect.Method.invokeNative(Native Method)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at java.lang.reflect.Method.invoke(Method.java:525)
09-19 18:54:51.165: E/AndroidRuntime(31543):	at android.view.View$1.onClick(View.java:3628)
09-19 18:54:51.165: E/AndroidRuntime(31543):	... 11 more
09-19 18:54:51.165: E/AndroidRuntime(31543): Caused by: java.lang.NullPointerException
09-19 18:54:51.165: E/AndroidRuntime(31543):	at com.example.myfirstapp.MainActivity.sendMessage(MainActivity.java:82)
09-19 18:54:51.165: E/AndroidRuntime(31543):	... 14 more

this is error i get in my logcat.