Since WordPress 4.3.0 you might get one or the other message like this one:
Notice: The called constructor method for WP_Widget in xyz is deprecated since version 4.3.0! Use __construct()
For plugins, I'd recommend looking for an update for this outdated plugin.
For your own code, or if you manually want to fix the plugin, modify the code as such (example);
Find this part of the code:
class t4a_stats_widget extends WP_Widget {
function t4a_stats_widget() {
$widget_ops = array('classname' => '', 'description' => 'Statistics overview' );
$this->WP_Widget('stats_widget', __('T4A Statistics', 'tweaking4all'), $widget_ops);
}
...
In this example replace "function t4a_stats_widget() {" with "function __construct() {",
and replace "$this->WP_Widget(" with "parent::__construct(", so your code looks like this:
(t4a_stats_widget is the name of the failing widget)
class t4a_stats_widget extends WP_Widget {
function __construct() {
$widget_ops = array('classname' => '', 'description' => 'Statistics overview' );
parent::__construct('stats_widget', __('T4A Statistics', 'tweaking4all'), $widget_ops);
}
...
Rinse and repeat for all error messages and the errors will disappear.