OOP concepts in PHP 5 in brief

OOP concepts in PHP 5 in brief

OOP concepts in PHP 5 in short

Why this short — note? if you are familiar with OOD and any OOP language such as Java/C++, this short note will give you enough information to start with PHP 5 OOP Class

• Class definition starts with the keyword class, followed by a class name (non reserved word), followed by a pair of curly braces. The curly braces contain the definition of the classes members and methods
• You can create objects based on the classes. $obj = new className()
• You use $obj->methodName() to access a class method (public). You can use className::classMember to access class members (static): to use :: operator the method does not need to be declared static
• Inside a class all class methods have access to $this variable to refer to the calling object (if called from/using an object)
• member declaration: public $var = ‘a default value
• Default value always is: constant expression
• Class/Object Functions
• A class can use extends keyword to inherit methods and members of another class
• Multiple inheritance is not allowed
• To avoid using a long list of includes in the beginning of php files, you can use __autoload() function to do the job for you
• When you try to use an undefined class/interface an __autoload function is automatically called
• function __autoload($class_name) {
  require_once $class_name . ‘.php’;
  }
• Constructor syntax: void __construct ([ mixed $args [, $… ]] )
• Parents’ constructors are not automatically called from children’s constructor. use explicit parent::__construct() instead
• Destructor syntax: void __destruct ( void )
• Destructor is called: 1. all references to the object are removed 2. the object is explicitly destroyed 3. in shutdown sequence
• Parents’ destructors are not automatically called from children’s destructors. use explicit parent::__destruct() instead
• Access modifiers for class members: public, protected or private: Public — accessible from anywhere. Protected — accessible from inherited and parent classes, within the class. Private — accessible within the class
• No access modifier = public
• :: — scope resolution operator — allows access to static, constant, and overridden members or methods of a class
• Abstract classes: Introduced in PHP 5. You are not allowed to reate an instance of an abstract class.
• Even if a class contains one abstract method, the class must bedeclared abstract
• Abstract classes are just about signatures, they cannot define the implementation
• A class inheriting from an abstract class, must have to implement all abstract methods. The abstract methods must be defined with the same/(less restricted) visibility
• Interface: Just the method signatures. No method implementation inside interfaces
• All interface methods must be public
• Classes implementing interfaces must implement all methods. Classes use implements keyword to implement an interface
• A class can not implement two interfaces having same class names
• Interfaces can be extended using extends keyword
• Interfaces can also have constants
• Overloading: Overloading in PHP = dynamically “create” members and methods
• overloading methods: invoked when interacting with non-declared/invisible members or methods
• All overloading methods must be defined as public
• In PHP, overloading is done through magic methods
• The arguments of the magic methods can not be ‘passed by reference’
• Member overloading methods: void __set ( string $name , mixed $value ), mixed __get ( string $name ), bool __isset ( string $name ), void __unset ( string $name )
• Method overloading: mixed __call ( string $name , array $arguments ), mixed __callStatic ( string $name , array $arguments )
• Object Iteration: Inside the class
• foreach($this as $key => $value) {
  print “$key => $valuen”;
  }
• Object Iteration: Outside class:
• $class = new MyClass();
  foreach ($class as $key => $value) {
  print “$key => $valuen”;
  }
• Patterns: Factory Pattern: allows the instantiation of objects at runtime
• Patterns: Singleton: Helps in situations where only a single instance of a class is required that will be used by many other objects
• Magic methods: have special meaning. __construct, __destruct (see Constructors and Destructors), __call, __callStatic, __get, __set, __isset, __unset, __sleep, __wakeup, __toString, __set_state and __clone
• serialize() — applies to __sleep(). unserialize() applies to __wakeup()
• final keyword: final members can not be overriden, final classes can not be extended
• $copy_of_object = clone $object; : will create a clone of $object. Unless a __clone method defined, a shadow is created. __clone() method can define how the cloning will be done
• Objects Comparison: == : two object instances are equal if they have the same attributes and values, and are instances of the same class.
• Objects Comparison: === : Object variables are identical if and only if they refer to the same instance of the same class
• Reflection APIs: to reverse-engineer classes, interfaces, functions and methods, extensions
• Reflection APIs: Offer ways to retrieve doc comments for functions, classes and methods
• Type Hinting: Functions can enforce parameters to be objects:
• Late Static Bindings: to refer the called class in a context of static inheritance.
• — — -

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