Interface and Abstract classes in php with syntax and examples

Interfaces define a contract that must be implemented by any class that implements it. They cannot be instantiated and only contain method declarations.

Syntax:


interface InterfaceName {
  public function method1();
  public function method2();
}


Example:


interface Printable {
  public function print();
}

class Document implements Printable {
  public function print() {
    echo "Printing document...";
  }
}

class Image implements Printable {
  public function print() {
    echo "Printing image...";
  }
}


Abstract Classes in PHP:

Abstract classes cannot be instantiated and are designed to be inherited by other classes. They can contain both abstract and concrete methods.

Syntax:


abstract class ClassName {
  abstract public function abstractMethod();
  public function concreteMethod() {
    // code
  }
}


Example:


abstract class Animal {
  abstract public function sound();
  public function eat() {
    echo "Eating...";
  }
}

class Dog extends Animal {
  public function sound() {
    echo "Barking...";
  }
}

class Cat extends Animal {
  public function sound() {
    echo "Meowing...";
  }
}


Key differences:

- Interfaces:
    - Cannot contain concrete methods
    - Multiple interfaces can be implemented
    - Only contain method declarations
- Abstract Classes:
    - Can contain both abstract and concrete methods
    - Only one abstract class can be inherited
    - Can contain state (properties)

Best Practices:

1. Use interfaces for defining contracts
2. Use abstract classes for providing base implementation
3. Keep interfaces small and focused
4. Use abstract classes for shared functionality
5. Test implementation of interfaces and abstract classes

By understanding interfaces and abstract classes in PHP, you can create robust, maintainable, and scalable code that follows object-oriented principles