Creating PHP class instance with a string

You can simply use the following syntax to create a new class (this is handy if you're creating a factory):

$className = $whatever;
$object = new $className;

As an (exceptionally crude) example factory method:

public function &factory($className) {

    require_once($className . '.php');
    if(class_exists($className)) return new $className;

    die('Cannot create new "' . $className . '" class - includes not found or class unavailable.');
}

have a look at example 3 from http://www.php.net/manual/en/language.oop5.basic.php

$className = 'Foo';
$instance = new $className(); // Foo()

Lets say ClassOne is defined as:

public class ClassOne
{
    protected $arg1;
    protected $arg2;

    //Contructor
    public function __construct($arg1, $arg2)
    {
        $this->arg1 = $arg1;
        $this->arg2 = $arg2;
    }

    public function echoArgOne
    {
        echo $this->arg1;
    }

}

Using PHP Reflection;

$str = "One";
$className = "Class".$str;
$class = new \ReflectionClass($className);

Create a new Instance:

$instance = $class->newInstanceArgs(["Banana", "Apple")]);

Call a method:

$instance->echoArgOne();
//prints "Banana"

Use a variable as a method:

$method = "echoArgOne";
$instance->$method();

//prints "Banana"

Using Reflection instead of just using the raw string to create an object gives you better control over your object and easier testability (PHPUnit relies heavily on Reflection)

Yes, you can!

$str = 'One';
$class = 'Class'.$str;
$object = new $class();

When using namespaces, supply the fully qualified name:

$class = '\Foo\Bar\MyClass'; 
$instance = new $class();

Other cool stuff you can do in php are:
Variable variables:

$personCount = 123;
$varname = 'personCount';
echo $$varname; // echo's 123

And variable functions & methods.

$func = 'my_function';
$func('param1'); // calls my_function('param1');

$method = 'doStuff';
$object = new MyClass();
$object->$method(); // calls the MyClass->doStuff() method.