File review request

app/public/wp-content/plugins/wp10-midlevel1/wp10-midlevel1.php

@@ -0,0 +1,54 @@
+<?php
+/**
+* Plugin Name: Test1
+* Description: カリキュラム用プラグインです
+* Version: 1.0.0
+* Requires at least: 5.5.1
+* Requires PHP: 7.2
+* Author: Ei Thandar Aung
+* License: GPL v2 or later
+* License URI: https://www.gnu.org/licenses/gpl-2.0.html
+*/
+
+// ①
+if ( ! defined( 'ABSPATH' ) ) {
+    exit;
+ }
+
+ class My_Test1 {
+    // ②
+    private static $instance;
+
+    public static function get_instance() {
+       if ( ! isset( self::$instance ) ) {
+          self::$instance = new self();
+       }
+       return self::$instance;
+    }
+
+    public function __construct() {
+
+       add_action( 'my_page', array( $this, 'add_my_page' ), 10 );
+    }
+
+    // ④
+    public function add_my_page() {
+        add_my_page(
+            __( 'Test1 Page', '' ),
+            __( "Test1 Page", '' ),
+            'administrator',
+            'my_test1',
+            array( $this, 'view_test1_page' ),
+        );
+    }
+    public function view_test1_page() {
+        //please create alert box
+
+        ?>
+        <script>alert("Hello World");</script>
+               <h1>Test1 Page</h1>
+               <p>This is test page.</p>
+        <?php
+    }
+ }
+ My_Test1::get_instance();