In android app Toolbar.setTitle method has no effe

Question

I'm trying to create simple application using android-support-v7:21 library.

Code snippets:
MainActivity.java

public class MainActivity extends ActionBarActivity {

    Toolbar mActionBarToolbar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mActionBarToolbar = (Toolbar) findViewById(R.id.toolbar_actionbar);            
        mActionBarToolbar.setTitle("My title");
        setSupportActionBar(mActionBarToolbar);
}

activity_main.xml

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    android:orientation="vertical">

    <android.support.v7.widget.Toolbar            
        android:id="@+id/toolbar_actionbar"
        android:background="@null"
        android:layout_width="match_parent"
        android:layout_height="?actionBarSize"
        android:fitsSystemWindows="true" />

</LinearLayout>

But instead of "My title" on Toolbar %application name% is shown.
Seems like setTitle method has no effect.
I would like to show "My title".

UPD: Before, styles.xml was:

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="windowActionBar">false</item>
</style>

So, I thought that actionbar is not used. I add NoActionBar to style parent:

<style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
    <item name="windowActionBar">false</item>
</style>

But the problem is not resolved.

Answer 1

In Kotlin you can do this:

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.appcompat.widget.Toolbar

class SettingsActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_settings)

        val toolbar = findViewById<Toolbar>(R.id.toolbar)
        setSupportActionBar(toolbar)
        supportActionBar?.setDisplayHomeAsUpEnabled(true)
        supportActionBar?.setTitle(R.string.title)

    }

    override fun onSupportNavigateUp() = true.also { onBackPressed() }

}

Answer 2

Make sure you add this option:

getSupportActionBar().setDisplayOptions(ActionBar.DISPLAY_SHOW_TITLE);