Application doesn't have Action bar when starts

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XML

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Android

i want to make an Action bar Menu for my page in android studio. but when i run the app there is no Action bar.
i write the menu XML codes in menu_main.xml like this:

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools" tools:context=".MainActivity">

    <item
    android:id="@+id/SigningUp"
            showAsAction="ifRoom|withText"
         android:title="ثبت نام"/>
   </menu>

and this is my java code:

    public static final int SIGN_UP_ID = Menu.FIRST;
    public static final int EXIT_APP_ID = Menu.FIRST + 1;

@Override
    public boolean onCreateOptionsMenu(Menu menu) {
        boolean result = super.onCreateOptionsMenu(menu);

        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_main, menu);

        menu.add(0, SIGN_UP_ID, 0, R.string.sign_up);
        menu.add(0, EXIT_APP_ID, 0, R.string.exit_application);


        return result;
    }

    @Override
    public boolean onMenuItemSelected(int featureId, MenuItem item) {

        switch(item.getItemId())
        {
            case SIGN_UP_ID:
                Intent i = new Intent(LoggingIn.this, signingUp.class);
                startActivity(i);
                return true;
            case EXIT_APP_ID:

                return true;
        }

        return super.onMenuItemSelected(featureId, item);
    }