Calling the addJavascriptInterface method of the android.webkit.WebView class allows the web pages of a WebView to access a Java object's methods via JavaScript.

Objects exposed to JavaScript are available in all frames of the WebView.

If you need to expose Java objects to JavaScript, guarantee that no untrusted third-party content is loaded into the WebView.

In the following (bad) example, a Java object is exposed to JavaScript.

Android Documentation: addJavascriptInterface