Text not getting displayed in emulator

<resources>

    <string name="app_name">My Application</string>
    <string name="textview">"@string/textview"</string>
    <string name="action_settings">Settings</string>

</resources>

------
 <textview>
        android:id="@+id/main_textview"
        android:text="@string/textview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="20dp"
        android:layout_marginTop="20dp"

    />

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity {
    TextView mainTextView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 1. Access the TextView defined in layout XML
        // and then set its text
        mainTextView = (TextView) findViewById(R.id.main_textview);
        mainTextView.setText("Set in Java!");

    }