How to create widget post in sidebar

<?php
/*
Plugin Name: flippercode Widget Pack
Plugin URI: http://flippercode.com
Description: A plugin containing various widgets created in a Flippercode series on WordPress widgets
Version: 0.1
Author: flippercode
Author URI: http://flippercode.com
Text Domain: flippercode
License: GPLv2

*/


class FlipperText_Widget extends WP_Widget {

    public function __construct() {
    
        parent::__construct(
            'flippertext_widget',
            __( 'Flipper Text Widget', 'flippertextdomain' ),
            array(
                'classname'   => 'flippertext_widget',
                'description' => __( 'A basic text widget to demo the flipper series on creating your own widgets.', 'flippertextdomain' )
                )
        );
      
        load_plugin_textdomain( 'flippertextdomain', false, basename( dirname( __FILE__ ) ) . '/languages' );
      
    }

    /** 
     * Front-end display of widget.
     *
     * @see WP_Widget::widget()
     *
     * @param array $args     Widget arguments.
     * @param array $instance Saved values from database.
     */
 public function widget( $args, $instance ) {
        if ( ! isset( $args['widget_id'] ) ) {
            $args['widget_id'] = $this->id;
        }

        $title = ( ! empty( $instance['title'] ) ) ? $instance['title'] : __( 'Recent Posts' );

        /** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
        $title = apply_filters( 'widget_title', $title, $instance, $this->id_base );

        $number = ( ! empty( $instance['number'] ) ) ? absint( $instance['number'] ) : 2;
        if ( ! $number )
            $number = 5;
        $show_date = isset( $instance['show_date'] ) ? $instance['show_date'] : false;

        /**
         * Filter the arguments for the Recent Posts widget.
         *
         * @since 3.4.0
         *
         * @see WP_Query::get_posts()
         *
         * @param array $args An array of arguments used to retrieve the recent posts.
         */
        $r = new WP_Query( apply_filters( 'widget_posts_args', array(
            'posts_per_page'      => $number,
            'no_found_rows'       => true,
            'post_status'         => 'publish',
            'ignore_sticky_posts' => true
        ) ) );

        if ($r->have_posts()) :
        ?>
        <?php echo $args['before_widget']; ?>
        <?php if ( $title ) {
            echo $args['before_title'] . $title . $args['after_title'];
        } ?>
        <ul>
        <?php while ( $r->have_posts() ) : $r->the_post(); ?>
            <li>
                <a href="<?php the_permalink(); ?>"><?php get_the_title() ? the_title() : the_ID(); ?></a>
            <?php if ( $show_date ) : ?>
                <span class="post-date"><?php echo get_the_date(); ?></span>
            <?php endif; ?>
            </li>
        <?php endwhile; ?>
        </ul>
        <?php echo $args['after_widget']; ?>
        <?php
        // Reset the global $the_post as this query will have stomped on it
        wp_reset_postdata();

        endif;
    }

 
    /**
      * Sanitize widget form values as they are saved.
      *
      * @see WP_Widget::update()
      *
      * @param array $new_instance Values just sent to be saved.
      * @param array $old_instance Previously saved values from database.
      *
      * @return array Updated safe values to be saved.
      */
    public function update( $new_instance, $old_instance ) {       
        
        $instance = $old_instance;
        $instance['title'] = sanitize_text_field( $new_instance['title'] );
        $instance['number'] = (int) $new_instance['number'];
        $instance['show_date'] = isset( $new_instance['show_date'] ) ? (bool) $new_instance['show_date'] : false;
        return $instance;
        
    }
 
    /**
      * Back-end widget form.
      *
      * @see WP_Widget::form()
      *
      * @param array $instance Previously saved values from database.
      */
    public function form( $instance ) {   
    
        $title     = isset( $instance['title'] ) ? esc_attr( $instance['title'] ) : '';
        $number    = isset( $instance['number'] ) ? absint( $instance['number'] ) : 2;
        $show_date = isset( $instance['show_date'] ) ? (bool) $instance['show_date'] : false;
        ?>
        
        <p><label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
        <input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo $title; ?>" /></p>

        <p><label for="<?php echo $this->get_field_id( 'number' ); ?>"><?php _e( 'Number of posts to show:' ); ?></label>
        <input class="tiny-text" id="<?php echo $this->get_field_id( 'number' ); ?>" name="<?php echo $this->get_field_name( 'number' ); ?>" type="number" step="1" min="1" value="<?php echo $number; ?>" size="3" /></p>

        <p><input class="checkbox" type="checkbox"<?php checked( $show_date ); ?> id="<?php echo $this->get_field_id( 'show_date' ); ?>" name="<?php echo $this->get_field_name( 'show_date' ); ?>" />
        <label for="<?php echo $this->get_field_id( 'show_date' ); ?>"><?php _e( 'Display post date?' ); ?></label></p>
    
    <?php
    }
    
}

/* Register the widget */
add_action( 'widgets_init', function(){
     register_widget( 'flippertext_widget' );
});