PHP Alert Dialog in webview

Activity.jave
here is onpagefinished() method
http://developer.android.com/reference/android/webkit/WebViewClient.html#onPageFinished(android.webkit.WebView, java.lang.String)

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

String ss = "sdffffffffffffffffffffffff rgfvdg dfgh";
web = (WebView) findViewById(R.id.webView1);

web.setWebViewClient(new WebViewClient() {
@Override
public void onPageFinished(WebView view, String url) {

web.loadUrl("javascript:(function() { alert('hai'); })()");
}
});

web.setWebChromeClient(new WebChromeClient());
web.getSettings().setJavaScriptEnabled(true);
web.loadDataWithBaseURL("", ss, "text/html", "UTF-8", " ");
}

XML R.layout.activity_main

   <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/tabhost"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <WebView
        android:id="@+id/webView1"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

output