WP widget

class-widget.php

/**
     * new WordPress Widget format
     * Wordpress 2.8 and above
     * @see http://codex.wordpress.org/Widgets_API#Developing_Widgets
     */
    class PREFIX_Name_Widget extends WP_Widget {

        /**
         * Constructor
         *
         * @return void
         **/
        function PREFIX_Name_Widget() {
            $widget_ops = array( 'classname' => 'CSS class name', 'description' => 'Description' );
            $this->WP_Widget( 'CSS class name', 'Title', $widget_ops );
        }

        /**
         * Outputs the HTML for this widget.
         *
         * @param array  An array of standard parameters for widgets in this theme
         * @param array  An array of settings for this widget instance
         * @return void Echoes it's output
         **/
        function widget( $args, $instance ) {
            extract( $args, EXTR_SKIP );
            echo $before_widget;
            echo $before_title;
            echo 'Title'; // Can set this with a widget option, or omit altogether
            echo $after_title;

        //
        // Widget display logic goes here
        //

        echo $after_widget;
        }

        /**
         * Deals with the settings when they are saved by the admin. Here is
         * where any validation should be dealt with.
         *
         * @param array  An array of new settings as submitted by the admin
         * @param array  An array of the previous settings
         * @return array The validated and (if necessary) amended settings
         **/
        function update( $new_instance, $old_instance ) {

            // update logic goes here
            $updated_instance = $new_instance;
            return $updated_instance;
        }

        /**
         * Displays the form for this widget on the Widgets page of the WP Admin area.
         *
         * @param array  An array of the current settings for this widget
         * @return void Echoes it's output
         **/
        function form( $instance ) {
            $instance = wp_parse_args( (array) $instance, array( array of option_name => value pairs ) );

            // display field names here using:
            // $this->get_field_id( 'option_name' ) - the CSS ID
            // $this->get_field_name( 'option_name' ) - the HTML name
            // $instance['option_name'] - the option value
        }
    }

example2.php

<?php
/**
 * @package Kinsta_widget
 * @version 1.0
 */
/*
Plugin Name: Kinsta Widget
Plugin URI: http://wordpress.org/extend/plugins/#
Description: This is an example plugin 
Author: Your Name
Version: 1.0
Author URI: http://example.com/
*/
class Kinsta_Widget extends WP_Widget {
	/**
	 * Sets up the widgets name etc
	 *
	 * @link https://developer.wordpress.org/reference/classes/wp_widget/__construct/
	 * @see https://developer.wordpress.org/reference/functions/wp_register_sidebar_widget/
	 *
	 */
	public function __construct() {}
	/**
	 * Outputs the content of the widget on front-end
	 *
	 * @param array $args Widget arguments 
	 * @param array $instance 
	 *
	 * @link https://developer.wordpress.org/reference/classes/wp_widget/widget/
	 */
	public function widget( $args, $instance ) {}
	/**
	 * Outputs the options form on admin
	 *
	 * @param array $instance The widget options
	 *
	 * @link https://developer.wordpress.org/reference/classes/wp_widget/form/
	 */
	public function form( $instance ) {}
	/**
	 * Processing widget options on save
	 *
	 * @param array $new_instance The new options
	 * @param array $old_instance The previous options
	 *
	 * @link https://developer.wordpress.org/reference/classes/wp_widget/update/
	 */
	public function update( $new_instance, $old_instance ) {}
}
// register Kinsta_Widget
add_action( 'widgets_init', function(){
	register_widget( 'Kinsta_Widget' );
});