[Solved] App crahing when Button declared outside onCreate method [duplicate]

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If you want a reference to your button globally then you should declare it outside then initialize it in onCreate

Button b1; //declare the button variable

public class SharedPreferencesActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_shared_preferences);

    b1 = (Button) findViewById(R.id.buttonSave); //initialize on creation
}

You should read more into the basics of Java when learning Android

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solved App crahing when Button declared outside onCreate method [duplicate]