PHP类与对象的基础概念

类声明与类的实例化

class : 声明类
new : 类的实例化

class User
{
    public $name = 'jack';
    public $age = 28;
}
$user = new User ();

类的静态成员与类的扩展

static : 声明静态成员
调用静态成员用类名::静态成员

class User
{
    public $name = 'jack';
    public $age = 28;
    public static $gender = 'male';
    public static function show(){
        return self::$gender;
    }
}
echo User::$gender; // 输出 male
echo User::show(); // 输出 male

trait功能

trait 是类似于类的声明，用use调用，但是不能实例化

trait User
{
    public $name = 'jack';
    public $age = 28;
    public static $gender = 'male';
    public static function show(){
        return self::$gender;
    }
}
class People
{
    use User;
}
$people = new People();
echo $people->show();//输出： male

trait与父类的区别与联系

基类>trait>父类

trait User
{
    public $name = 'jack';
    public $age = 28;
    public $gender = 'male';
    public function show(){
        echo '这个是User的show';
    }
}
class Person
{
    public function show(){
        echo '这个是Person的show';
    }
}
class People extends Person
{
    use User;
    public function show(){
        echo '这个是People的show';
    }
}
$people = new People();
echo $people->show();

• 基类存在则输出的show();
  

• 基类不存在则输出trait的show();
  

• 都不存在则输出父类的show();