PHP

<?php
class SimpleClass
{
    // property declaration
    public $var = 'a default value';

    // method declaration
    public function displayVar()
    {
        echo $this->var;
    }
}
$obj = new SimpleClass();
$obj->displayVar();
echo "<br>";
$obj->var = "a new value";        // change a public property
$obj->displayVar();
?>

<?php
class A
{
    function foo()
    {
        if (isset($this)) {
            echo '$this is defined (' . get_class($this) . ")<br>";
        } else {
            echo "\$this is not defined.<br>";
        }
    }
}
$a = new A();
$a->foo();
?>

<?php
class Foo { public $name = "Foo object"; }

$instance = new Foo();
$className = 'Foo';
$second = new $className();      // same as new Foo()
echo $instance->name . "<br>";
echo get_class($second) . "<br>";
var_dump($instance instanceof Foo);
?>

class SimpleClass
{
    // valid property declarations (constant expressions):
    public $var1 = 'hello ' . 'world';    // allowed since PHP 5.6
    public $var2 = <<<EOD
hello world
EOD;
    public $var3 = 1 + 2;                 // allowed since PHP 5.6
    public $var6 = MY_CONSTANT;
    public $var7 = array(true, false);
    public int $count = 0;                // typed property (PHP 7.4)

    // invalid property declarations:
    // public $var4 = self::myStaticMethod();   – function call
    // public $var5 = $myVar;                   – variable
}

<?php
class MyClass
{
    const CONSTANT = 'constant value';
    const GST = 18;

    function showConstant()
    {
        echo self::CONSTANT . "<br>";
    }
}
echo MyClass::CONSTANT . "<br>";
$classname = "MyClass";
echo $classname::CONSTANT . "<br>";
$class = new MyClass();
$class->showConstant();
echo $class::CONSTANT . "<br>";
echo "GST rate: " . MyClass::GST . "%";
?>

public function __construct(mixed ...$args)

<?php
class BaseClass
{
    function __construct()
    {
        print "In BaseClass constructor<br>";
    }
}
class SubClass extends BaseClass
{
    function __construct()
    {
        parent::__construct();
        print "In SubClass constructor<br>";
    }
}
$obj = new BaseClass();
$obj = new SubClass();
?>

<?php
class Student
{
    public function __construct(
        public string $name,
        public int $roll,
        private float $fees = 0
    ) {}

    public function show(): string
    {
        return "Roll $this->roll: $this->name (fees Rs. $this->fees)";
    }
}
$s1 = new Student("Asha", 101, 4500);
$s2 = new Student("Ravi", 102);
echo $s1->show() . "<br>";
echo $s2->show();
?>

<?php
class MyDestructableClass
{
    public $name;
    function __construct()
    {
        print "In constructor<br>";
        $this->name = "MyDestructableClass";
    }
    function __destruct()
    {
        print "Destroying " . $this->name . "<br>";
    }
}
$obj = new MyDestructableClass();
echo "Working with the object...<br>";
unset($obj);                 // destructor runs here
echo "End of script.";
?>

<?php
class Account
{
    public $holder = "Asha";
    protected $type = "Savings";
    private $balance = 5000;

    public function showBalance() { return "Balance: Rs. $this->balance"; }
}
class SavingsAccount extends Account
{
    public function info() { return "$this->holder has a $this->type account"; }
}
$acc = new SavingsAccount();
echo $acc->holder . "<br>";
echo $acc->info() . "<br>";
echo $acc->showBalance() . "<br>";
echo $acc->balance;          // private – not accessible
?>

<?php
class Foo
{
    public function printItem($string)
    {
        echo 'Foo: ' . $string . "<br>";
    }
    public function printPHP()
    {
        echo 'PHP is great.' . "<br>";
    }
}
class Bar extends Foo
{
    public function printItem($string)
    {
        echo 'Bar: ' . $string . "<br>";
    }
}
$foo = new Foo();
$bar = new Bar();
$foo->printItem('baz');  // Output: 'Foo: baz'
$foo->printPHP();        // Output: 'PHP is great'
$bar->printItem('baz');  // Output: 'Bar: baz'
$bar->printPHP();        // Output: 'PHP is great'
?>

<?php
class SimpleClass
{
    public $var = 'a default value';
    public function displayVar() { echo $this->var . "<br>"; }
}
class ExtendClass extends SimpleClass
{
    // Redefine the parent method
    function displayVar()
    {
        echo "Extending class<br>";
        parent::displayVar();
    }
}
$extended = new ExtendClass();
$extended->displayVar();
?>

<?php
class MyClass
{
    const CONST_VALUE = 'A constant value';
}
$classname = 'MyClass';
echo $classname::CONST_VALUE . "<br>";
echo MyClass::CONST_VALUE;
?>

<?php
class MyClass
{
    const CONST_VALUE = 'A constant value';
}
class OtherClass extends MyClass
{
    public static $my_static = 'static var';

    public static function doubleColon()
    {
        echo parent::CONST_VALUE . "<br>";
        echo self::$my_static . "<br>";
    }
}
$classname = 'OtherClass';
$classname::doubleColon();
OtherClass::doubleColon();
?>

<?php
class MyClass
{
    protected function myFunc()
    {
        echo "MyClass::myFunc()<br>";
    }
}
class OtherClass extends MyClass
{
    // Override parent's definition
    public function myFunc()
    {
        // But still call the parent function
        parent::myFunc();
        echo "OtherClass::myFunc()<br>";
    }
}
$class = new OtherClass();
$class->myFunc();
?>

<?php
class Foo
{
    public static $my_static = 'foo';
    public function staticValue()
    {
        return self::$my_static;
    }
}
class Bar extends Foo
{
    public function fooStatic()
    {
        return parent::$my_static;
    }
}
print Foo::$my_static . "<br>";
$foo = new Foo();
print $foo->staticValue() . "<br>";
print $foo::$my_static . "<br>";
$classname = 'Foo';
print $classname::$my_static . "<br>";
print Bar::$my_static . "<br>";
$bar = new Bar();
print $bar->fooStatic() . "<br>";
print $foo->my_static . "<br>";   // Undefined property – static is not accessible with ->
?>

<?php
class Visitor
{
    public static int $count = 0;
    public function __construct() { self::$count++; }
    public static function total(): string
    {
        return "Visitors created: " . self::$count;
    }
}
new Visitor(); new Visitor(); new Visitor();
echo Visitor::total();
?>

<?php
class MyClass1
{
    public function hello() { return "MyClass1 loaded from MyClass1.php"; }
}

<?php
spl_autoload_register(function ($class_name) {
    echo "Autoloader: loading $class_name<br>";
    include $class_name . '.php';
});
$obj  = new MyClass1();
$obj2 = new MyClass2();
echo $obj->hello() . "<br>";
echo $obj2->hello();
?>

<?php
spl_autoload_register(function ($name) {
    echo "Want to load $name.<br>";
    throw new Exception("Unable to load $name.");
});
try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage();
}
?>