php面向对象精要(2)

1，self与parent关键字

>self指向当前的类，常用来访问静态成员，方法和常量

>parent指向父类，常用来调用父类的构造函数和方法和成员，也可以用来访问常量

<?php
class Ancestor {
    const NAME = "Ancestor";
    function __construct(){
        echo self::NAME . PHP_EOL;
    }
}
    
class Child extends Ancestor {
    const NAME = "Child";
    function __construct () {
        parent::__construct();
        echo self::NAME . PHP_EOL;
    }
}

$obj = new Child();
?>

2，instanceof

>判断一个对象是否是某个类的实例

>判断一个对象是否实现了某个接口

<?php

    class Rectangle {
        public $name = __CLASS__;
    }

    class Square extends Rectangle {
        public $name = __CLASS__;
    }

    class Circle {
        public $name = __CLASS__;
    }

    function checkIfRectangle( $shape ) {
        if( $shape instanceof Rectangle ) {
            echo $shape->name . PHP_EOL;
        }
    }

    checkIfRectangle( new Square() );
    checkIfRectangle( new Rectangle() );
    checkIfRectangle( new Circle() );
?>

 3，abstract类和方法

>抽象类不能被实例化

>抽象方法必须被重写

>只要有一个方法声明为abstract，这个类必须声明为abstract的，当然可以直接把这个类声明为抽象类

<?php
abstract class Shape {
    protected $x;
    protected $y;
    function setCenter( $x, $y ) {
        $this->x = $x;
        $this->y = $y;
    }
    
    abstract function draw();
    abstract function show();
}

class Square extends Shape {
    function draw() {
    }
    function show(){
    }
}

class Circle extends Shape {
    function draw(){
    }
    function show(){
    }
}

?>

4，interface

>接口类似c++的多重继承,  class A implements B, C ... {}

>实现了该接口的类，都将与该接口形成是一关系 (instanceof )

>多重接口之前不能互相冲突( 指的是定义相同的常量和方法 )

interface Loggable {
    function logString();
}

class Person implements Loggable {
    private $name;
    private $age;
    function __construct( $name, $age ){
        $this->name = $name;
        $this->age = $age;
    }
    function logString() {
        return "Class Person: name = {$this->name}, age = {$this->age}" . PHP_EOL;
    }
}

class Product implements Loggable {
    private $name;
    private $price;
    function __construct( $name, $price ){
        $this->name = $name;
        $this->price = $price;
    }

    function logString() {
        return "Class Product: name = {$this->name}, price = {$this->price}" . PHP_EOL;
    }
}

function MyLog( $obj ) {
    if ( $obj instanceof Loggable ) {
        echo $obj->logString();
    }else {
        echo $obj . "没有实现Loggable接口";
    }
}

$p = new Person( "ghostwu", 20 );
echo $p->logString();
$goods = new Product( "book", 19.99 );
echo $goods->logString();
MyLog( $p );
MyLog( $goods );