Custom Widget Code With Default Value

if( ! function_exists('function_name') ){
	function function_name(){
		register_widget('class_name');
	}
	add_action('widgets_init', 'function_name');
}


class class_name extends WP_Widget{
	function __construct(){
		parent::__construct(
			'class_name',
			__('Widget Display Name', 'text-domain'),
			array('description' => __('widget description', 'text-domain'))
		);
	}

	public function widget($args, $instance){
		extract( $args );
		$title = apply_filters( 'widget_title', $instance[ 'title' ] );
		$show_tag = $instance['show_tag'];
	    // The following variable is for a checkbox option type
	    $post_count = $instance[ 'post_count' ] ? 'true' : 'false';


		
		echo  $args['before_widget'];
		if ( $title ) {
        echo $before_title . $title . $after_title;
    }


	
		echo $args['after_widget'];
	}

	public function form( $instance ) {
		$defaults = array( 'title' => __( 'Default Title', 'bestblog' ), 'post_count' => 'on' );
	    $instance = wp_parse_args( ( array ) $instance, $defaults ); ?>
	    <p>
	        <label for="<?php echo $this->get_field_id( 'title' ); ?>">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 esc_attr( $instance[ 'title' ] ); ?>" />
	    </p>
		<p>
		<label for="<?php echo $this->get_field_id( 'show_tag' ); ?>">Number of tags to show:</label>
		<input class="tiny-text" id="<?php echo $this->get_field_id( 'show_tag' ); ?>" name="<?php echo $this->get_field_name( 'show_tag' ); ?>" type="text" value="<?php echo esc_attr( $instance[ 'show_tag' ] ); ?>" />
		</p>

	    <!-- The checkbox -->
	    <p>
	        <input class="checkbox" type="checkbox" <?php checked( $instance[ 'post_count' ], 'on' ); ?> id="<?php echo $this->get_field_id( 'post_count' ); ?>" name="<?php echo $this->get_field_name( 'post_count' ); ?>" /> 
	        <label for="<?php echo $this->get_field_id( 'post_count' ); ?>">Show Tag Post Count</label>
	    </p>
		<?php 
	}

	function update( $new_instance, $old_instance ) {
	    $instance = $old_instance;
	    $instance[ 'title' ] = strip_tags( $new_instance[ 'title' ] );
	    $instance[ 'show_tag' ] = $new_instance[ 'show_tag' ];
	    // The update for the variable of the checkbox
	    $instance[ 'post_count' ] = $new_instance[ 'post_count' ];
	    return $instance;
	}
}