应用场景如： 缓存（文件、redis…）,数据库操作（mysql,oracle,pgsql…）

1.策略模式

<?php 

/**
* abstract class
*/
abstract class Strategy
{
    // 算法方法
    abstract public function AlgorithmInterface();    
}

/**
* 算法a
*/
class ConcreteStrategyA extends Strategy
{
    public function AlgorithmInterface()
    {
        echo "算法a实现\n";
    }
}


/**
* 算法b
*/
class ConcreteStrategyB extends Strategy
{
    public function AlgorithmInterface()
    {
        echo "算法b实现\n";
    }
}

/**
* 算法c
*/
class ConcreteStrategyC extends Strategy
{
    public function AlgorithmInterface()
    {
        echo "算法c实现\n";
    }
}

/**
* 上下文context
*/
class Context
{
    private $strategy;

    function __construct($strategy)
    {
        $this->strategy = $strategy;
    }

    public function contextInterface()
    {
        $this->strategy->AlgorithmInterface();
    }
}

$context = new Context(new ConcreteStrategyA());
$context->contextInterface();

$context = new Context(new ConcreteStrategyB());
$context->contextInterface();

$context = new Context(new ConcreteStrategyC());
$context->contextInterface();

2.策略模式和简单工厂结合

<?php

// 只需要修改上方的Context类
class Context
{
    private $strategy;

    function __construct($operation)
    {
        switch ($operation) {
            case 'a':
                $this->strategy = new ConcreteStrategyA();
                break;
            case 'b':
               $this->strategy = new ConcreteStrategyB();
                break;
            case 'c':
                $this->strategy = new ConcreteStrategyC();
                break;
        }
    }

    public function contextInterface()
    {
        return $this->strategy->AlgorithmInterface();
    }
}

//客户端代码
$context = new Context('a');
$context->contextInterface();