php基础--取默认值以及类的继承

（1）对于php的默认值的使用和C++有点类似，都是在函数的输入中填写默认值，以下是php方法中对于默认值的应用：

<?php
function makecoffee($types = array("cappuccino"), $coffeeMaker = NULL)
{
    $device = is_null($coffeeMaker) ? "hands" : $coffeeMaker;
    return " </br> Making a cup of ".join(", ", $types)." with $device.
";
}
echo makecoffee();
echo makecoffee(array("cappuccino", "lavazza"), "teapot");

function makeyogurt($flavour, $type = "acidophilus")
{
    return "</br>Making a bowl of $type $flavour.
";
}
echo makeyogurt("raspberry");  

?> 

以上程序的输出为：

当输入为空时，当前的值采用默认的值，当不为空时，采用输入值；

（2）以下是PHP中对于class中默认值的使用：

<?php

class pot{
    
    protected $x;
    protected $y;
    protected $c;
    public function __construct($x = 0, $y=1){
        
        $this->x = $x;
        $this->y = $y;  
        $this->c = $this->x+$this->y;
    }
    
    function printC()
    {
        echo "</br>".$this->c;
    }
}

$pot1 = new pot(9, 6);
$pot1->printC();
$pot2 = new pot();
$pot2->printC();

?>

输出结果为：

（三）继承取默认值：

(1)当继承的class有construct的情况：

<?php
class pot{
    
    protected $x;
    protected $y;
    protected $c;
    public function __construct($x = 0, $y=1){
        
        $this->x = $x;
        $this->y = $y;
        
        $this->c = $this->x+$this->y;
    }
    
    function printC()
    {
        echo "</br>".$this->c;
    }
}

class pots extends pot{
    protected $x;
    protected $y;
    protected $c;
    public function __construct($x = 10, $y = 20){
        
        $this->x = $x;
        $this->y = $y;
        $this->c = $this->x+$this->y;
    }
}
$pots1 = new pots(10, 5);
$pots1->printC();
$pots2 = new pots();
$pots2->printC();

?>

当继承的class有自己的construct，那它的取值为自身的construct的取值, 对于自身的construct没有默认值，则默认取0值， 对于自身没有的方法，继承父类的方法；

以上的输出结果为：

(2)当继承的class没有construct的情况，取父类的值：

<?php
class pot{
    
    protected $x;
    protected $y;
    protected $c;
    public function __construct($x = 0, $y=1){
        
        $this->x = $x;
        $this->y = $y;
        
        $this->c = $this->x+$this->y;
    }
    
    function printC()
    {
        echo "</br>".$this->c;
    }
}

class pots extends pot{
      
}
$pots1 = new pots(10, 5);
$pots1->printC();
$pots2 = new pots();
$pots2->printC();

?>

以上输出结果为：