找工作的你不容错过的45个PHP面试题附答案（下篇）

/**
 * Singleton class
 *
 */
final class UserFactory {
    *
     * Call this method to get singleton
     *
     * @return UserFactory
     */
    public static
    function Instance() {
        static $inst = null;
        if ($inst === ) {
            new UserFactory();
        }
        return $inst;
    }

    *
     * Private ctor so nobody else can instantiate it
     *
     private
     __construct() {

    }
}

$fact = UserFactory::Instance();
$fact2 = UserFactory::Instance();

$fact = new UserFactory()

$name = $firstName ?? $username ?? $placeholder ?? "Guest"; 

function adder(&$str2) {  
    $str2 .= 'Call By Reference';  
}
$str = 'This is ';  
adder($str);  
echo $str;

This is Call By Reference

$a = "Original";
$my_array = array("a" => "Cat","b" => "Dog","c" => "Horse");
extract($my_arrayecho "$a = $a; $b = $b; $c = $c";

$a = Cat; $b = Dog; $c = Horse

function getTotal($tax)
{
    $total = 0.00;

    $callback =
        function ($quantity,$product) use ($tax,&$total)
        {
            $pricePerItem = constant(__CLASS__ . "::PRICE_" .
                strtoupper($product));
            $total += ($pricePerItem * $quantity) * ($tax + 1.0);
        };

    array_walk($this->products,1)">$callback);
    return round($total,2);
}

 Car {
     run() {
        static::getName();
    }

    private  getName() {
        return 'Car';
    }
}

class Toyota extendsreturn 'Toyota'echo Car::run(); // Output: Car
echo Toyota::run();  Output: Toyota

$start = microtime(truewhile (...) {

}
$time_elapsed_secs = true) - $start;

We have this:
$objectA->a;
b;
$objectB->c;
d;

We want the easiest way to get:
$objectC->$objectC->d;

$obj_merged = (object) array_merge((array) $obj1,($obj2);

foreach($objectA as $k => $v) $objectB->$k = $v;

Comparing Integers
echo 1 <= > 1; outputs 0
echo 3 <= > 4; outputs -1
echo 4 <= > 3; outputs 1

//String Comparison

echo "x" <= > "x";  0
echo "x" <= > "y"; -1
echo "y" <= > "x"; 1

 Student 
{
   protected $id;
   $name etc.

   function __construct(){
       $this->id = ;
       other members are still uninitialised
   }

   $row_from_database$row_from_database->id;
       $this->name = name;
        etc.
   }
}

 Student
{
     __construct() {
         allocate your stuff
    }

    static function withID(  ) {
        $instance =  self();
        $instance->loadByID(  );
        $instancefunction withRow( array $row$instance->fill( protected function loadByID(  ) {
         do query
        $row = my_awesome_db_access_stuff(  );
        $this->fill(  );
    }

    function fill(  fill all properties from array
    }
}

$student = Student::withID( $id );

$firstName;
    $lastName etc.

    *
     * Constructor
     *
     * Static constructor / factory
      create() {
         self();
        *
     * FirstName setter - fluent style
     function setFirstName( ) {
        $this->firstName = $this*
     * LastName setter - fluent style
     function setLastName( $this->lastName =  create instance
$student= Student::create()->setFirstName("John")->setLastName("Doe");

 myFunc() {
    for ($i = 0; $i < func_num_args(); $i++) {
        printf("Argument %d: %sn",1)">$i,func_get_arg($i));
    }
}


Argument 0: a
Argument 1: 2
Argument 2: 3.5
*/
myFunc('a',2,3.5);