What's the duration of webview cache

Question

In my app, I have a webview with the following setting.

    WebSettings settings = webView.getSettings();
    settings.setJavaScriptEnabled(true);
    settings.setDatabaseEnabled(true);
    settings.setAppCacheEnabled(true);
    settings.setAppCachePath(this.getContext().getCacheDir().getAbsolutePath());
    settings.setDomStorageEnabled(true);
    settings.setDisplayZoomControls(false);

In the setting, we set the cache to true. Now my question is, what's the cache expiry mechanism? If we didn't do anything to it, what's the default cache timeout? (Hopefully it is not forever, until someone explicitly clear the cache of the app manually).