Public Private Php
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Public Private Php
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Keywords are the words used as a reserve in a program that has a special meaning assigned to them. They can be a command or parameter. Like every other programming language, PHP also has a set of special words called keywords which cannot be used as variable names for other purposes. They are also called as reserved names.
A private keyword, as the name suggests is the one that can only be accessed from within the class in which it is defined. All the keywords are by default under the public category unless they are specified as private or protected. Private keywords help in security purposes by giving the least visibility to the keyword in the entire code. It is also easier to refractor when there is only a single class calling this keyword .
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Apart from private keywords, there can also be private methods too. In object-oriented programming , methods are the set of procedures associated with any class. In the case of private methods, they are allowed to be called only within methods belonging to the same class or its module.
There are also private constants and properties which can be declared. The visibility in these cases is limited only between their classes and not instances. If the two objects are of the same type then one object can call another object’s private method.
Any variable, property or a method can be declared private by prefixing it with a “private” keyword.
Let us understand the working of private property in PHP by taking the below example:
Output 2: After commenting on line 23.
Output 3: After commenting on line 24.
Output 4: After commenting on lines 46, 47 and 40.
Explanation to the above code: When you run this code entirely, you are bound to get fatal errors at a few line numbers like the line:25,26,45,52,53. We are first declaring all 3 properties public, private and protected in the main class PHPExample to display their respective words. Inline 25, we are trying to access all 3 properties from the PHPExample class. Since private and protected examples cannot be accessible outside their class, we get a fatal error in the output as shown and only public property is displayed.
In the second half of the code, we are declaring another class PHPExample2 where we are re-declaring the display values for protected and public properties. The same is not allowed for private and then we are performing the same action as in the first half. Since we are trying to call private property which is not declared here, we get undefined property error.
Let us understand the working of the private method and keywords in PHP by taking the below example:
Output 2: After commenting lines 32, 33 and 36.
Explanation to the above code: In the above example, $first_name and $last_name are declared as private variables of class NameExample and therefore they cannot be directly called using a class object. Hence when we first try to run the code we get an error as “Undefined variable: first_name in /workspace/NameExample.php on line 32” and the same goes for line 33. When we comment on these 2 lines and run the code again we get the error “Uncaught Error: Call to a member function name() on null in /workspace/NameExample.php:36”.
This is because we have declared function fName as private and it is trying to access the same. The code runs smoothly when line 36 is also commented and displays from method name since it is a public method.
Below are the Advantages of Using Private in PHP:
Following are the Rules and Regulations to be followed for Private in PHP:
Private is a way of restricting the accessibility of variables, methods or properties of a class. They can only be accessed in the class they are declared and not from any subclass which extends from it. Any protected property from a parent class can be overridden by a subclass and made public but cannot be made as private.
This is a guide to Private in PHP. Here we discuss two different examples of Private in PHP with advantages and rules and regulations to be followed in it. You can also go through our other related articles to learn more –
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public ; echo $this -> protected ; echo $this -> private ; } } $obj = new MyClass (); echo $obj -> public ; // Works echo $obj -> protected ; // Fatal Error echo $obj -> private ; // Fatal Error $obj -> printHello (); // Shows Public, Protected and Private /** * Define MyClass2 */ class MyClass2 extends MyClass { // We can redeclare the public and protected properties, but not private public $public = 'Public2' ; protected $protected = 'Protected2' ; function printHello () { echo $this -> public ; echo $this -> protected ; echo $this -> private ; } } $obj2 = new MyClass2 (); echo $obj2 -> public ; // Works echo $obj2 -> protected ; // Fatal Error echo $obj2 -> private ; // Undefined $obj2 -> printHello (); // Shows Public2, Protected2, Undefined ?>
MyPublic (); $this -> MyProtected (); $this -> MyPrivate (); } } $myclass = new MyClass ; $myclass -> MyPublic (); // Works $myclass -> MyProtected (); // Fatal Error $myclass -> MyPrivate (); // Fatal Error $myclass -> Foo (); // Public, Protected and Private work /** * Define MyClass2 */ class MyClass2 extends MyClass { // This is public function Foo2 () { $this -> MyPublic (); $this -> MyProtected (); $this -> MyPrivate (); // Fatal Error } } $myclass2 = new MyClass2 ; $myclass2 -> MyPublic (); // Works $myclass2 -> Foo2 (); // Public and Protected work, not Private class Bar { public function test () { $this -> testPrivate (); $this -> testPublic (); } public function testPublic () { echo "Bar::testPublic\n" ; } private function testPrivate () { echo "Bar::testPrivate\n" ; } } class Foo extends Bar { public function testPublic () { echo "Foo::testPublic\n" ; } private function testPrivate () { echo "Foo::testPrivate\n" ; } } $myFoo = new Foo (); $myFoo -> test (); // Bar::testPrivate // Foo::testPublic ?>
foo (); // Public, Protected and Private work /** * Define MyClass2 */ class MyClass2 extends MyClass { // This is public function foo2 () { echo self :: MY_PUBLIC ; echo self :: MY_PROTECTED ; echo self :: MY_PRIVATE ; // Fatal Error } } $myclass2 = new MyClass2 ; echo MyClass2 :: MY_PUBLIC ; // Works $myclass2 -> foo2 (); // Public and Protected work, not Private ?>
foo = $foo ; } private function bar () { echo 'Accessed the private method.' ; } public function baz ( Test $other ) { // We can change the private property: $other -> foo = 'hello' ; var_dump ( $other -> foo ); // We can also call the private method: $other -> bar (); } } $test = new Test ( 'test' ); $test -> baz (new Test ( 'other' )); ?>
string(5) "hello"
Accessed the private method.
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User Contributed Notes 27 notes
INSIDE CODE and OUTSIDE CODE label = 'Ink-Jet Tatoo Gun' ; $item -> price = 49.99 ; ?> Ok, that's simple enough... I got it inside and out. The big problem with this is that the Item class is COMPLETELY IGNORANT in the following ways: * It REQUIRES OUTSIDE CODE to do all the work AND to know what and how to do it -- huge mistake. * OUTSIDE CODE can cast Item properties to any other PHP types (booleans, integers, floats, strings, arrays, and objects etc.) -- another huge mistake. Note: we did it correctly above, but what if someone made an array for $price? FYI: PHP has no clue what we mean by an Item, especially by the terms of our class definition above. To PHP, our Item is something with two properties (mutable in every way) and that's it. As far as PHP is concerned, we can pack the entire set of Britannica Encyclopedias into the price slot. When that happens, we no longer have what we expect an Item to be. INSIDE CODE should keep the integrity of the object. For example, our class definition should keep $label a string and $price a float -- which means only strings can come IN and OUT of the class for label, and only floats can come IN and OUT of the class for price. label and $item->price, * by using the protected keyword. * 2. FORCE the use of public functions. * 3. ONLY strings are allowed IN & OUT of this class for $label * via the getLabel and setLabel functions. * 4. ONLY floats are allowed IN & OUT of this class for $price * via the getPrice and setPrice functions. */ protected $label = 'Unknown Item' ; // Rule 1 - protected. protected $price = 0.0 ; // Rule 1 - protected. public function getLabel () { // Rule 2 - public function. return $this -> label ; // Rule 3 - string OUT for $label. } public function getPrice () { // Rule 2 - public function. return $this -> price ; // Rule 4 - float OUT for $price. } public function setLabel ( $label ) // Rule 2 - public function. { /** * Make sure $label is a PHP string that can be used in a SORTING * alogorithm, NOT a boolean, number, array, or object that can't * properly sort -- AND to make sure that the getLabel() function * ALWAYS returns a genuine PHP string. * * Using a RegExp would improve this function, however, the main * point is the one made above. */ if( is_string ( $label )) { $this -> label = (string) $label ; // Rule 3 - string IN for $label. } } public function setPrice ( $price ) // Rule 2 - public function. { /** * Make sure $price is a PHP float so that it can be used in a * NUMERICAL CALCULATION. Do not accept boolean, string, array or * some other object that can't be included in a simple calculation. * This will ensure that the getPrice() function ALWAYS returns an * authentic, genuine, full-flavored PHP number and nothing but. * * Checking for positive values may improve this function, * however, the main point is the one made above. */ if( is_numeric ( $price )) { $this -> price = (float) $price ; // Rule 4 - float IN for $price. } } } ?> Now there is nothing OUTSIDE CODE can do to obscure the INSIDES of an Item. In other words, every instance of Item will always look and behave like any other Item complete with a label and a price, AND you can group them together and they will interact without disruption. Even though there is room for improvement, the basics are there, and PHP will not hassle you... which means you can keep your hair!
If you have problems with overriding private methods in extended classes, read this:)
The manual says that "Private limits visibility only to the class that defines the item". That means extended children classes do not see the private methods of parent class and vice versa also.
As a result, parents and children can have different implementations of the "same" private methods, depending on where you call them (e.g. parent or child class instance). Why? Because private methods are visible only for the class that defines them and the child class does not see the parent's private methods. If the child doesn't see the parent's private methods, the child can't override them. Scopes are different. In other words -- each class has a private set of private variables that no-one else has access to.
A sample demonstrating the percularities of private methods when extending classes:
overridden ();
}
private function overridden () {
echo 'base' ;
}
}
class child extends base {
private function overridden () {
echo 'child' ;
}
}
$test = new child ();
$test -> inherited ();
?>
Output will be "base".
If you want the inherited methods to use overridden functionality in extended classes but public sounds too loose, use protected. That's what it is for:)
A sample that works as intended:
overridden ();
}
protected function overridden () {
echo 'base' ;
}
}
class child extends base {
protected function overridden () {
echo 'child' ;
}
}
$test = new child ();
$test -> inherited ();
?>
Output will be "child".
Just a quick note that it's possible to declare visibility for multiple properties at the same time, by separating them by commas. eg:
A class A static public function can access to class A private function : foo (); } } $a = new A (); A :: bar ( $a ); ?> It's working.
private , $this -> public \n" ; } } class B extends A { function __construct () { $this -> private = 2 ; $this -> public = 2 ; } function set () { $this -> private = 3 ; $this -> public = 3 ; } function get () { return parent :: get () . "B: $this -> private , $this -> public \n" ; } } $B = new B ; echo $B -> get (); echo $B -> set (); echo $B -> get (); ?> ?> Result is A: 1 , 2 B: 2 , 2 A: 1 , 3 B: 3 , 3 This is correct code and does not warn you to use any private. "$this->private" is only in A private. If you write it in class B it's a runtime declaration of the public variable "$this->private", and PHP doesn't even warn you that you create a variable in a class without declaration, because this is normal behavior.
Beware: Visibility works on a per-class-base and does not prevent instances of the same class accessing each others properties! bar , "\n" ; } public function setBar ( $value ) { // Neccessary method, for $bar is invisible outside the class $this -> bar = $value ; } public function setForeignBar ( Foo $object , $value ) { // this does NOT violate visibility! $object -> bar = $value ; } } $a = new Foo (); $b = new Foo (); $a -> setBar ( 1 ); $b -> setBar ( 2 ); $a -> debugBar ( $b ); // 2 $b -> debugBar ( $a ); // 1 $a -> setForeignBar ( $b , 3 ); $b -> setForeignBar ( $a , 4 ); $a -> debugBar ( $b ); // 3 $b -> debugBar ( $a ); // 4 ?>
Please note that protected methods are also available from sibling classes as long as the method is declared in the common parent. This may also be an abstract method. In the below example Bar knows about the existence of _test() in Foo because they inherited this method from the same parent. It does not matter that it was abstract in the parent. _test (); } } class Foo extends Base { pr
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