What is an abstract class in PHP

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What is an abstract class in PHP   How can it be used

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An abstract class is a class that is only partially implemented by the programmer. It may contain one or more abstract methods. An abstract method is simply a function definition that serves to tell the programmer that the method must be implemented in a child class.

There is good explanation of that here.

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An abstract class is like the normal class it contains variables it contains protected variables functions it contains constructor only one thing is different it contains abstract method   The abstract method means an empty method without definition so only one difference in abstract class we can not create an object of abstract class  Abstract must contains the abstract method and those methods must be defined in its inheriting class

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Abstract Class   1  Contains an abstract method  2  Cannot be directly initialized  3  Cannot create an object of abstract class  4  Only used for inheritance purposes  Abstract Method  1  Cannot contain a body  2  Cannot be defined as private  3  Child classes must define the methods declared in abstract class   Example Code   abstract class A       public function test1             echo  Hello World             abstract protected function f1        abstract public function f2        protected function test2            echo  Hello World test            class B extends A       public  a    India       public function f1             echo  F1 Method Call             public function f2             echo  F2 Method Call             b   new B    echo  b- gt test1       lt br  gt    echo  b- gt a     lt br  gt    echo  b- gt test2       lt br  gt    echo  b- gt f1       lt br  gt    echo  b- gt f2       lt br  gt      Output   Hello World India Hello World test F1 Method Call F2 Method Call

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Abstract classes are classes that contain one or more abstract methods  An abstract method is a method that is declared  but contains no implementation  Abstract classes may not be instantiated  and require subclasses to provide implementations for the abstract methods    1   Can not instantiate abstract class  Classes defined as abstract may not be instantiated  and any class that contains at least one abstract method must also be abstract   Example below     abstract class AbstractClass        abstract protected function getValue        abstract protected function prefixValue  prefix         public function printOut             echo  Hello how are you              obj new AbstractClass     obj- gt printOut      Fatal error  Cannot instantiate abstract class AbstractClass   2  Any class that contains at least one abstract method must also be abstract  Abstract class can have abstract and non-abstract methods  but it must contain at least one abstract method  If a class has at least one abstract method  then the class must be declared abstract      Note  Traits support the use of abstract methods in order to impose requirements upon the exhibiting class    Example below     class Non Abstract Class      abstract protected function getValue         public function printOut             echo  Hello how are you              obj new Non Abstract Class     obj- gt printOut      Fatal error  Class Non Abstract Class contains 1 abstract method and must therefore be declared abstract or implement the remaining methods  Non Abstract Class  getValue    3  An abstract method can not contain body  Methods defined as abstract simply declare the method s signature - they cannot define the implementation  But a non-abstract method can define the implementation   abstract class AbstractClass      abstract protected function getValue       return  Hello how are you              public function printOut             echo  this- gt getValue       n            class ConcreteClass1 extends AbstractClass       protected function getValue             return  ConcreteClass1              public function prefixValue  prefix            return    prefix ConcreteClass1             class1   new ConcreteClass1   class1- gt printOut    echo  class1- gt prefixValue  FOO       n     Fatal error  Abstract function AbstractClass  getValue   cannot contain body   4  When inheriting from an abstract class  all methods marked abstract in the parent s class declaration must be defined by the child  If you inherit an abstract class you have to provide implementations to all the abstract methods in it   abstract class AbstractClass          Force Extending class to define this method     abstract protected function getValue            Common method     public function printOut             print  this- gt getValue       lt br  gt             class ConcreteClass1 extends AbstractClass       public function printOut             echo  dhairya             class1   new ConcreteClass1   class1- gt printOut      Fatal error  Class ConcreteClass1 contains 1 abstract method and must therefore be declared abstract or implement the remaining methods  AbstractClass  getValue    5  Same  or a less restricted  visibility When inheriting from an abstract class  all methods marked abstract in the parent s class declaration must be defined by the child  additionally  these methods must be defined with the same  or a less restricted  visibility  For example  if the abstract method is defined as protected  the function implementation must be defined as either protected or public  but not private      Note that abstract method should not be private    abstract class AbstractClass        abstract public function getValue        abstract protected function prefixValue  prefix            public function printOut             print  this- gt getValue             class ConcreteClass1 extends AbstractClass       protected function getValue             return  ConcreteClass1              public function prefixValue  prefix            return    prefix ConcreteClass1            class1   new ConcreteClass1   class1- gt printOut    echo  class1- gt prefixValue  FOO       lt br  gt      Fatal error  Access level to ConcreteClass1  getValue   must be public  as in class AbstractClass    6   Signatures of the abstract methods must match When inheriting from an abstract class  all methods marked abstract in the parent s class declaration must be defined by the child the signatures of the methods must match  i e  the type hints and the number of required arguments must be the same  For example  if the child class defines an optional argument  where the abstract method s signature does not  there is no conflict in the signature   abstract class AbstractClass        abstract protected function prefixName  name       class ConcreteClass extends AbstractClass         public function prefixName  name   separator                  if   name     Pacman                  prefix    Mr             elseif   name     Pacwoman                  prefix    Mrs             else                prefix                         return    prefix   separator    name              class   new ConcreteClass  echo  class- gt prefixName  Pacman      lt br  gt    echo  class- gt prefixName  Pacwoman      lt br  gt      output  Mr  Pacman           Mrs  Pacwoman   7  Abstract class doesn t support multiple inheritance Abstract class can extends another abstract class Abstract class can provide the implementation of interface But it doesn t support multiple inheritance   interface MyInterface      public function foo        public function bar       abstract class MyAbstract1      abstract public function baz        abstract class MyAbstract2 extends MyAbstract1 implements MyInterface      public function foo    echo  foo         public function bar    echo  bar         public function baz    echo  baz        class MyClass extends MyAbstract2      obj new MyClass   obj- gt foo     obj- gt bar     obj- gt baz      output  foobarbaz      Note  Please note order or positioning of the classes in your code can affect the interpreter and can cause a Fatal error    So  when using multiple levels of abstraction  be careful of the positioning of the classes within the source code    below example will cause Fatal error  Class  horse  not found  class cart extends horse       public function get breed     return  Wood        abstract class horse extends animal       public function get breed     return  Jersey        abstract class animal       public abstract function get breed        cart   new cart    print  cart- gt get breed

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Abstract Class  contains only declare the method s signature  they can t define the implementation  Abstraction class are defined using the keyword abstract   Abstract Class is not possible to implement multiple inheritance  Latest version of PHP 5 has introduces abstract classes and methods  Classes defined as abstract   we are unable to create the object   may not instantiated

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An abstract class is a class that contains at least one abstract method  which is a method without any actual code in it  just the name and the parameters  and that has been marked as  abstract    The purpose of this is to provide a kind of template to inherit from and to force the inheriting class to implement the abstract methods   An abstract class thus is something between a regular class and a pure interface  Also interfaces are a special case of abstract classes where ALL methods are abstract   See this section of the PHP manual for further reference

[php] What is an abstract class in PHP?

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