php魔术方法——构造函数和析构函数,php魔术构造函数
php有一类很神奇的方法,这些方法是保留方法,通常不会在外部被显式调用,他们使用双下划线(__)开头,他们被称为魔术方法(Magic Methods)。php官方也不建议定义其他双下划线开头的方法。
这次介绍最常见的魔术方法:构造函数和析构函数。
1. 构造函数(__construct)
void __construct ([ <span>mixed</span> <span>$args</span> [, $... ]] )
构造函数:拥有构造函数的类会在每次创建新对象时先调用此方法,所以非常适合在使用对象前做一些初始化服务。
注意:
1. clone并不会调用构造函数
2. 如果子类定义了构造函数,则不会隐式调用父类的构造函数
3. 子类的构造函数允许和父类的构造函数参数不一致
4. 如果子类没有定义构造函数,php会尝试寻找父类的构造函数
5. 如果父类没有定义构造函数,使用parent关键字显式调用父类构造函数,会导致致命错误
<span> 1</span> <?<span>php </span><span> 2</span> <span> 3</span> <span>class</span><span> P{ </span><span> 4</span> <span> 5</span> <span>public</span> <span>function</span><span> __construct(){ </span><span> 6</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span> 7</span> <span> } </span><span> 8</span> <span> 9</span> <span>} </span><span>10</span> <span>11</span> <span>class</span> C1 <span>extends</span><span> P{ </span><span>12</span> <span>13</span> <span>public</span> <span>function</span><span> __construct(){ </span><span>14</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span>15</span> <span> } </span><span>16</span> <span>17</span> <span>} </span><span>18</span> <span>19</span> <span>class</span> C2 <span>extends</span><span> P{ </span><span>20</span> <span>21</span> <span>public</span> <span>function</span><span> __construct(){ </span><span>22</span> parent::<span>__construct(); </span><span>23</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span>24</span> <span> } </span><span>25</span> <span>26</span> <span>} </span><span>27</span> <span>28</span> <span>class</span> C3 <span>extends</span><span> P{ </span><span>29</span> <span>30</span> <span>} </span><span>31</span> <span>32</span> <span>//</span><span> P</span> <span>33</span> <span>$ins</span> = <span>new</span><span> P(); </span><span>34</span> <span>35</span> <span>//</span><span> Nothing</span> <span>36</span> <span>$ins2</span> = <span>clone</span> <span>$ins</span><span>; </span><span>37</span> <span>38</span> <span>//</span><span> C1</span> <span>39</span> <span>new</span><span> C1(); </span><span>40</span> <span>41</span> <span>//</span><span> P </span><span>42</span> <span>// C2</span> <span>43</span> <span>new</span><span> C2(); </span><span>44</span> <span>45</span> <span>//</span><span> P</span> <span>46</span> <span>new</span> C3();
除了魔术方法的构造函数,php还支持与类名相同的构造函数,不过优先级比魔术方法低:
<span> 1</span> <?<span>php </span><span> 2</span> <span> 3</span> <span>class</span><span> C1{ </span><span> 4</span> <span> 5</span> <span>public</span> <span>function</span><span> C1(){ </span><span> 6</span> <span>echo</span> <span>__CLASS__</span> . "1\n"<span>; </span><span> 7</span> <span> } </span><span> 8</span> <span> 9</span> <span>public</span> <span>function</span><span> __construct(){ </span><span>10</span> <span>echo</span> <span>__CLASS__</span> . "2\n"<span>; </span><span>11</span> <span> } </span><span>12</span> <span>13</span> <span>} </span><span>14</span> <span>15</span> <span>class</span><span> C2{ </span><span>16</span> <span>17</span> <span>public</span> <span>function</span><span> C2(){ </span><span>18</span> <span>echo</span> <span>__CLASS__</span> . "1\n"<span>; </span><span>19</span> <span> } </span><span>20</span> <span>21</span> <span>} </span><span>22</span> <span>23</span> <span>class</span><span> C3{ </span><span>24</span> <span>25</span> <span>public</span> <span>function</span><span> C3(){ </span><span>26</span> <span>echo</span> <span>__CLASS__</span> . "1\n"<span>; </span><span>27</span> <span> } </span><span>28</span> <span>29</span> <span>public</span> <span>function</span><span> __construct(){ </span><span>30</span> <span>echo</span> <span>__CLASS__</span> . "2\n"<span>; </span><span>31</span> <span>$this</span>-><span>C3(); </span><span>32</span> <span> } </span><span>33</span> <span>34</span> <span>} </span><span>35</span> <span>36</span> <span>//</span><span> C12</span> <span>37</span> <span>new</span><span> C1(); </span><span>38</span> <span>39</span> <span>//</span><span> C21</span> <span>40</span> <span>new</span><span> C2(); </span><span>41</span> <span>42</span> <span>//</span><span> C32 </span><span>43</span> <span>// C31</span> <span>44</span> <span>new</span> C3();
php5.3.3之后,在命名空间之内使用与类名同名的方法,不再作为构造函数,命名空间之外不变:
<span> 1</span> <?<span>php </span><span> 2</span> <span> 3</span> <span>namespace N; </span><span> 4</span> <span> 5</span> <span>class</span><span> C{ </span><span> 6</span> <span> 7</span> <span>public</span> <span>function</span><span> C(){ </span><span> 8</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span> 9</span> <span> } </span><span>10</span> <span>11</span> <span>} </span><span>12</span> <span>13</span> <span>//</span><span> Nothing</span> <span>14</span> <span>new</span> \N\C();
构造函数可以用全部三个访问控制修饰符,如单例模式:
<span> 1</span> <?<span>php </span><span> 2</span> <span> 3</span> <span>class</span><span> Single{ </span><span> 4</span> <span> 5</span> <span>public</span> <span>static</span> <span>function</span><span> getInstance(){ </span><span> 6</span> <span>static</span> <span>$ins</span> = <span>null</span><span>; </span><span> 7</span> <span>if</span>(<span>empty</span>(<span>$ins</span><span>)){ </span><span> 8</span> <span>$ins</span> = <span>new</span><span> self(); </span><span> 9</span> <span> } </span><span>10</span> <span>return</span> <span>$ins</span><span>; </span><span>11</span> <span> } </span><span>12</span> <span>13</span> <span>private</span> <span>function</span><span> __construct(){ </span><span>14</span> <span>echo</span> <span>__CLASS__</span> . "\n"<span>; </span><span>15</span> <span> } </span><span>16</span> <span>17</span> <span>} </span><span>18</span> <span>19</span> <span>//</span><span> Single</span> <span>20</span> Single::getInstance();
2. 析构函数(__destruct)
void __destruct ( void )
析构函数:析构函数会在某个对象的引用被全部删除或对象被显示销毁时执行。
注意:
1. 同构造函数类似,父类的析构函数并不会被引擎暗中调用,必须显式调用parent::__destruct
2. exit和die并不能阻止析构函数的执行
3. 致命错误会阻止析构函数的执行
4. 在析构函数中调用exit,可以阻止其他未执行的析构函数的执行
5. 如果父类没有定义析构函数,使用parent关键字显式调用父类析构函数,会导致致命错误
<?<span>php </span><span>class</span><span> P{ </span><span>function</span><span> __destruct(){ </span><span>echo</span> <span>get_class</span>(<span>$this</span>) . "\t" . <span>__CLASS__</span> . "\n"<span>; } } </span><span>class</span> C1 <span>extends</span><span> P{ </span><span>function</span><span> __destruct(){ </span><span>echo</span> <span>get_class</span>(<span>$this</span>) . "\t" . <span>__CLASS__</span> . "\n"<span>; } } </span><span>class</span> C2 <span>extends</span><span> P{ </span><span>function</span><span> __destruct(){ parent</span>::<span>__destruct(); </span><span>echo</span> <span>get_class</span>(<span>$this</span>) . "\t" . <span>__CLASS__</span> . "\n"<span>; } } </span><span>class</span> C3 <span>extends</span><span> P{ } </span><span>$insP</span> = <span>new</span><span> P(); </span><span>$ins1</span> = <span>new</span><span> C1(); </span><span>$ins2</span> = <span>new</span><span> C2(); </span><span>$ins3</span> = <span>new</span><span> C3(); </span><span>/*</span><span>* 输出: C3 P C2 P C2 C2 C1 C1 P P *</span><span>*/</span>

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

在PHP中,可以利用implode()函数的第一个参数来设置没有分隔符,该函数的第一个参数用于规定数组元素之间放置的内容,默认是空字符串,也可将第一个参数设置为空,语法为“implode(数组)”或者“implode("",数组)”。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。


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