The difference between 0 and null and false and empty in php

<?php
  
$test=0;
  
if($test==&#39;&#39;){
    echo &#39;<br />在php中，0即为空&#39;; //被输出
}
  
if($test===&#39;&#39;){
    echo &#39;<br />在php中，0即为空&#39;; //不被输出
}
  
if($test==NULL){
    echo &#39;<br />在php中，0即为空&#39;; //被输出
}
  
if($test===NULL){
    echo &#39;<br />在php中，0即为空&#39;; //不被输出
}
  
if($test==false){
    echo &#39;<br />在php中，0即为空&#39;; //被输出
}
  
if($test===false){
    echo &#39;<br />在php中，0即为空&#39;; //不被输出
}
  
?>