• 接口类使用关键字 interface 来定义，且类中所有方法都是抽象方法，修饰符为 public，无声明变量
• 类通过使用关键字 implement 来实现 interface 中的方法

interface User
{
    function getGender();
    function getLanguage();
}

class Male implements User
{
    function getGender()
    {
        return "Male";
    }

    function getLanguage()
    {
        return "Chinese";
    }
}

class Female implements User
{
    function getGender()
    {
        return "Female";
    }

    function getLanguage()
    {
        return "English";
    }
}

class Body
{
    function getUser(User $user)
    {
        echo "I am ".$user->getGender()."，and i speak ".$user->getLanguage();
    }
}
$body = new Body();
$body->getUser(new Male);
$body->getUser(new Female);

输出结果：I am Male，and i speak ChineseI am Female，and i speak English