What is the diffrence between super.loadUrl() and mainWebView.loadUrl()

ionic-v1
1

can any one explain what is the difference between below code blocks to load url.
in second code i have defined cordova webview on activity.xml

import org.apache.cordova.*;
public class HelloWorld extends CordovaActivity 
{
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        super.init();       
        super.loadUrl("file:///android_asset/www/index.html");
    }
}

vs

public class MyActivity extends CordovaActivity
{
    CordovaWebView mainView;
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        super.init();
        setContentView(R.layout.activity_my);
        mainView = (CordovaWebView) findViewById(R.id.mainView);
        Config.init(this);
        mainView.addJavascriptInterface(this, "JSInterface");
        mainView.loadUrl("file:///android_asset/www/Index.html" );
    }
}

Actually i wants to use JavascriptInterface to call some native functions from javascript the same javascript interface how can i use while loading using super.loadurl.