Définition
Le design pattern strategy définit une famille d'algorithmes, encapsule chacun d'eux, et les rend interchangeables. Il laisse l’algorithme changer indépendamment des clients qui les utilisent.
Diagramme UML
 |
| Diagramme de classes du design pattern strategy |
Exemple en PHP
// The classes that implement a concrete strategy should implement this
// The context class uses this to call the concrete strategy
interface Strategy
{
public function execute($a, $b);
}
// Implements the algorithm using the strategy interface
class ConcreteStrategyAdd implements Strategy
{
public function execute($a, $b)
{
echo 'Called ConcreteStrategyAdd\'s execute()' . "\n";
return $a + $b; // Do an addition with a and b
}
}
class ConcreteStrategySubtract implements Strategy
{
public function execute($a, $b)
{
echo 'Called ConcreteStrategySubtract\'s execute()' . "\n";
return $a - $b; // Do a subtraction with a and b
}
}
class ConcreteStrategyMultiply implements Strategy
{
public function execute($a, $b)
{
echo 'Called ConcreteStrategyMultiply\'s execute()' . "\n";
return $a * $b; // Do a multiplication with a and b
}
}
// Configured with a ConcreteStrategy object and maintains a reference
// to a Strategy object
class Context
{
private $strategy;
public function __construct(Strategy $strategy)
{
$this->setStrategy($strategy);
}
public function executeStrategy($a, $b)
{
return $this->strategy->execute($a, $b);
}
public function setStrategy(Strategy $strategy)
{
$this->strategy = $strategy;
}
}
// Three contexts following different strategies
$context = new Context(new ConcreteStrategyAdd());
echo $context->executeStrategy(3, 4) . "\n";
$context->setStrategy(new ConcreteStrategySubtract());
echo $context->executeStrategy(3, 4) . "\n";
$context->setStrategy(new ConcreteStrategyMultiply());
echo $context->executeStrategy(3, 4) . "\n";
L'exemple affiche :
Called ConcreteStrategyAdd's execute()
7
Called ConcreteStrategySubtract's execute()
-1
Called ConcreteStrategyMultiply's execute()
12
