NullPointerException when using database object

Question

I'm new to Android, and i've got some issues. It looks like it's saying DB.EmployeeOperations.open() is having an null object passed to it, but I'm not sure. Where I missed a step? Any help is appreciated.

Thanks in advance.

Logcat:

 *  06-10 16:10:52.605 17203-17203/com.androidtutorialpoint.employeemanagementsystem E/AndroidRuntime: FATAL EXCEPTION: main
        Process: com.androidtutorialpoint.employeemanagementsystem, PID: 17203
        java.lang.RuntimeException: Unable to resume activity {com.androidtutorialpoint.employeemanagementsystem/com.androidtutorialpoint.employeemanagementsystem.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.androidtutorialpoint.employeemanagementsystem.DB.EmployeeOperations.open()' on a null object reference
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3019)
        at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3050)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2425)
        at android.app.ActivityThread.access$900(ActivityThread.java:154)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5294)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
        Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.androidtutorialpoint.employeemanagementsystem.DB.EmployeeOperations.open()' on a null object reference
        at com.androidtutorialpoint.employeemanagementsystem.MainActivity.onResume(MainActivity.java:148)
        at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1257)
        at android.app.Activity.performResume(Activity.java:6076)
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3008)
        at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3050) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2425) 
        at android.app.ActivityThread.access$900(ActivityThread.java:154) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)

Java Code:

    public class MainActivity extends AppCompatActivity{

    private Button addEmployeeButton;
    private Button editEmployeeButton;
    private Button deleteEmployeeButton;
    private Button viewAllEmployeeButton;
    private EmployeeOperations employeeOps;
    private static final String EXTRA_EMP_ID = "com.androidtutorialpoint.empId";
    private static final String EXTRA_ADD_UPDATE = "com.androidtutorialpoint.add_update";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
        addEmployeeButton = (Button) findViewById(R.id.button_add_employee);
        editEmployeeButton = (Button) findViewById(R.id.button_edit_employee);
        deleteEmployeeButton = (Button) findViewById(R.id.button_delete_employee);
        viewAllEmployeeButton = (Button)findViewById(R.id.button_view_employees);



        addEmployeeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent i = new Intent(MainActivity.this,AddUpdateEmployee.class);
                i.putExtra(EXTRA_ADD_UPDATE, "Add");
                startActivity(i);
            }
        });
        editEmployeeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getEmpIdAndUpdateEmp();
            }
        });
        deleteEmployeeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getEmpIdAndRemoveEmp();
            }
        });
        viewAllEmployeeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent i = new Intent(MainActivity.this, ViewAllEmployees.class);
                startActivity(i);
            }
        });

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.employee_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if (id == R.id.menu_item_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }


    public void getEmpIdAndUpdateEmp(){

        LayoutInflater li = LayoutInflater.from(this);
        View getEmpIdView = li.inflate(R.layout.dialog_get_emp_id, null);

        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
        // set dialog_get_emp_id.xml to alertdialog builder
        alertDialogBuilder.setView(getEmpIdView);

        final EditText userInput = (EditText) getEmpIdView.findViewById(R.id.editTextDialogUserInput);

        // set dialog message
        alertDialogBuilder
                .setCancelable(false)
                .setPositiveButton("OK",new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog,int id) {
                                // get user input and set it to result
                                // edit text
                                Intent i = new Intent(MainActivity.this,AddUpdateEmployee.class);
                                i.putExtra(EXTRA_ADD_UPDATE, "Update");
                                i.putExtra(EXTRA_EMP_ID, Long.parseLong(userInput.getText().toString()));
                                startActivity(i);
                            }
                        }).create()
                .show();

    }


    public void getEmpIdAndRemoveEmp(){

        LayoutInflater li = LayoutInflater.from(this);
        View getEmpIdView = li.inflate(R.layout.dialog_get_emp_id, null);

        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
        // set dialog_get_emp_id.xml to alertdialog builder
        alertDialogBuilder.setView(getEmpIdView);

        final EditText userInput = (EditText) getEmpIdView.findViewById(R.id.editTextDialogUserInput);

        // set dialog message
        alertDialogBuilder
                .setCancelable(false)
                .setPositiveButton("OK",new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog,int id) {
                        // get user input and set it to result
                        // edit text
                        employeeOps = new EmployeeOperations(MainActivity.this);
                        employeeOps.removeEmployee(employeeOps.getEmployee(Long.parseLong(userInput.getText().toString())));
                        Toast t = Toast.makeText(MainActivity.this,"Employee removed successfully!",Toast.LENGTH_SHORT);
                        t.show();
                    }
                }).create()
                .show();

    }



    @Override
    protected void onResume() {
        super.onResume();
        employeeOps.open();
    }

    @Override
    protected void onPause() {
        super.onPause();
        employeeOps.close();

    }
}

I believe `onPause` gets called when the dialog is open anyway, so you would have gotten a closed database — OneCricketeer, Jun 11 '16 at 17:50

earthw0rmjim · Accepted Answer · 2016-06-11T17:45:48.380

0

The problem is you're calling employeeOps.open() in onResume(), but employeeOps is not instantiated yet, it's value is still null.

Take a look at the Activity lifecycle.

As you can see, when an Activity gets created two methods get called before onResume(): onCreate() and onStart().

If you would like to call the open() method of EmployeeOperations in onResume(), you need to have an instance of it by then.

Call the following in onCreate():

employeeOps = new EmployeeOperations(this);

edited Jun 11 '16 at 17:45

answered Jun 11 '16 at 17:29

earthw0rmjim

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Yeah. I've got it, that was the issue. Problem solved, Thank you! – Julius Jun 11 '16 at 18:07

score 0 · Answer 2 · answered Jun 11 '16 at 17:30

Your problem is a misunderstanding of the Android lifecycle. Specifically, from that resource,

Once the onCreate() finishes execution, the system calls the onStart() and onResume() methods in quick succession.

What this means for you is that onResume() triggers before you ever set employeeOps to a non-null value. You're only initializing it in response to a button press, but your Activity is only visible for a very short duration before onResume is triggered.

NullPointerException when using database object

2 Answers2