PHP设计模式------单例模式

<?php
namespace test;

class Singleton
{

    protected static $instance;

    private function __construct()
    {

    }
    /*
        static 的用法是后期静态绑定:根据具体的上下文环境，确定使用哪个类
    */
    public static function getInstance()
    {
        /*
            $instance 如果为NULL，新建实例对象
        */
        if (NULL === static::$instance) {
            echo ‘before‘ . PHP_EOL;
            static::$instance = new static();
            echo ‘after‘ . PHP_EOL;
        }

        /*
            不为NULL时，则直接返回已有的实例
        */
        return static::$instance;
    }
}

<?php
namespace test;

require_once(‘Singleton.php‘);

class SingletonTest extends Singleton
{
    private $name;

    public function __construct()
    {
        echo ‘Create SingletonTest instance‘ . PHP_EOL;
    }

    public function setName($name)
    {
        $this->name = $name;
    }

    public function getName()
    {
        echo $this->name . PHP_EOL;
    }
}

/*
    SingletonTest instance
*/
$test_one = SingletonTest::getInstance();
$test_one->setName(‘XiaoMing‘);
$test_one->getName();
/*
    $test_two 和 $test_one 获取的是同一个实例对象
*/
$test_two = SingletonTest::getInstance();
$test_two->getName();