详解PHP中instanceof关键字及instanceof关键字有什么作用

$manager = new Employee();
…
if ($manager instanceof Employee)
  echo "Yes";

class test{}
class test{}
class testChilern Extends test{}
$a = new test();
$m = new test();
$i = ($m instanceof test);
if($i)
  echo '$m是类test的实例！<br />'; // get this value
switch ($a instanceof test){
  case true :
    echo 'YES<br />';
    break;
  case false :
    echo 'No<br />'; //get this value
    break;
}
$d=new testChilern();
if($d instanceof test)echo '$d是类test的子类！<br />'; // get this value

<?php
$obj = new A();
if ($obj instanceof A) {
  echo 'A';
}

<?php
interface ExampleInterface
{
   public function interfaceMethod();
 }
 class ExampleClass implements ExampleInterface
{
   public function interfaceMethod()
   {
     return 'Hello World!';
   }
 }
$exampleInstance = new ExampleClass();
 if($exampleInstance instanceof ExampleInterface){
   echo 'Yes, it is';
 }else{
   echo 'No, it is not';
} 
?>

<?php
class Foo {
   public $foobar = 'Foo';
   public function test() {
     echo $this->foobar . "\n";
   }
 }
 class Bar extends Foo {
   public $foobar = 'Bar';
 }
$a = new Foo();
$b = new Bar();
echo "use of test() method\n";
$a->test();
$b->test();
echo "instanceof Foo\n";
var_dump($a instanceof Foo); // TRUE
var_dump($b instanceof Foo); // TRUE
echo "instanceof Bar\n";
var_dump($a instanceof Bar); // FALSE
var_dump($b instanceof Bar); // TRUE
echo "subclass of Foo\n";
var_dump(is_subclass_of($a, 'Foo')); // FALSE
var_dump(is_subclass_of($b, 'Foo')); // TRUE
echo "subclass of Bar\n";
var_dump(is_subclass_of($a, 'Bar')); // FALSE
var_dump(is_subclass_of($b, 'Bar')); // FALSE
?>