php面向?qū)ο笾甤lass
Jun 13, 2016 am 10:39 AM
下面來(lái)說(shuō)說(shuō) PHP中的Class,用于表達(dá)的語(yǔ)言都是非正式的語(yǔ)言。
建立一個(gè)類很簡(jiǎn)單:
class my_class {}
類到底干什么呢?很多人都說(shuō)是什么黑匣子,我在這里稱它為一個(gè)獨(dú)立的整體。我們只知道類名,而不知道里面有什么東西。那么,該如何使用這個(gè)類呢?
首先:要知道它里面是否定義了公共的變量--專業(yè)術(shù)語(yǔ)上稱它為“屬性”。
其次:要知道它里面定義了什么函數(shù)--專業(yè)術(shù)語(yǔ)中稱它為“方法”。
我都被這些專業(yè)術(shù)語(yǔ)搞糊涂了,所以干脆不理它了。
類中的如何定義公共變量,它有什么作用呢?
很簡(jiǎn)單,我們來(lái)擴(kuò)充 my_class 類:
class my_class
{
??? var $username;
}
看上面很簡(jiǎn)單,我們定義了一個(gè)公共的變量,只是用 var 空格 普通變量名 構(gòu)成。它有什么用呢?考慮一下函數(shù)中,如果我們要訪問(wèn)函數(shù)外的變量,是不是要先 global 一下呢?這個(gè)想實(shí)現(xiàn)的效果也是如此,它是想讓這個(gè)類中的所有函數(shù)都能訪問(wèn)它,而它區(qū)別于函數(shù)的一個(gè)地方,是類的外部也可以隨時(shí)訪問(wèn)和控制這個(gè)變量,我隨后再講外部如何訪問(wèn)它。還有一個(gè)區(qū)別,不能用復(fù)雜的語(yǔ)句給這個(gè)變量賦值(具體的等理解了類以后自己去看規(guī)則)。
給它一個(gè)默認(rèn)值:
class my_class
{
??? var $username = "深空";
}
OK,定義了一個(gè)公共的變量了,接下來(lái)定義一個(gè)函數(shù)(也就是所謂的“方法”):
class my_class
{
??? var $username = "深空";
??? function show_username()
??? {
??? }
}
這個(gè)定義函數(shù)跟普通的定義函數(shù)形式上沒什么區(qū)別了。簡(jiǎn)單就好,定義一個(gè)打印 $username 的函數(shù):
class my_class
{
??? var $username = "深空";
??? function show_username($username)
??? {
??????? echo $username;
??? }
}
到這里可能某些人開始迷糊了,呵呵,最關(guān)鍵的就是這里了,看清楚了?,F(xiàn)在有三個(gè) $username 了。到底哪個(gè)是哪個(gè)啊~~
函數(shù)所帶的形參,不用解釋了吧?這個(gè)函數(shù)功能就是打印形參所接收的值,也就是如果:
show_username("豬頭深空");
那么它將打印 “豬頭深空” ,就這么簡(jiǎn)單。
怎么樣訪問(wèn)這個(gè)函數(shù)?肯定不是我上面說(shuō)的那樣直接 show_username("豬頭深空"); 了,別急,類有類的一套。如下:
$Name = new my_class();
這樣就初始化上面的那個(gè) my_class 的類了,并把這個(gè)對(duì)象賦給變量 $Name ,你可以這樣理解,這個(gè)變量就代表整個(gè)類了,呵呵。
使用類中的函數(shù):
$Name->show_username("豬頭深空");
暈了,為什么這么復(fù)雜?還要箭頭?其實(shí)很形象的。本來(lái)已經(jīng)把類給了變量 $Name 了是吧?也就是 $Name 代表了這個(gè)類,然后用一個(gè)箭頭指向類中的 show_username 這個(gè)函數(shù)。就是這么簡(jiǎn)單,也就是說(shuō),這個(gè)函數(shù)是這個(gè)類中的,而不是其他的函數(shù)--你就理解為表示一個(gè)區(qū)別吧,呵呵。
試試看哦,打印出 “豬頭深空” 這四個(gè)字了。你說(shuō)為什么要這么復(fù)雜?用函數(shù)不是也能實(shí)現(xiàn)么?我說(shuō),這么簡(jiǎn)單的你當(dāng)然看不出好處了,我們繼續(xù)擴(kuò)充。
還有一個(gè)疑問(wèn)是:剛才說(shuō)的“公共的變量”怎么一點(diǎn)用處都沒有呢?為什么這個(gè)函數(shù)不會(huì)自動(dòng)接收這個(gè)公共變量 var $username 中的默認(rèn)值?也就是如果我使用:
$Name->show_username($username);
會(huì)有什么結(jié)果呢?答案是沒有任何輸出。因?yàn)槟銢]有給形參 $username 一個(gè)值。
那么該怎么使用這個(gè)公共的變量?我們來(lái)修改一下這個(gè)類:
class my_class
{
??? var $username = "深空";
??? function show_username()
??? {
??????? echo $this->username;
??? }
}
哇靠,不是吧,這回連形參都沒有了?還多了一個(gè)$this->,暈了不是,呵呵。其實(shí)這也是類的一個(gè)最大的方便之處。
$this 的作用:訪問(wèn)一個(gè)公共的變量,或者類里面的函數(shù)。
訪問(wèn)?這么專業(yè)?其實(shí)就是用 $this->username 來(lái)代替 var $username 而已拉,$this 用來(lái)說(shuō)明它是公共的、可以訪問(wèn)的、函數(shù)外部的東西(比如其他變量或函數(shù))。
試試看:
$Name->show_username();
看到了吧,終于打印 “深空” 這兩個(gè)字了,娃哈哈。
我不打印“深空”這兩個(gè)字,我要打印“豬頭深空”,怎么辦?很簡(jiǎn)單,我們給這個(gè)公共變量重新賦值拉。服了你了。
$Name->username = "豬頭深空";
這個(gè)能明白意思么?$Name->username 表示的是類里面的這個(gè)公共變量。等號(hào)賦值不用我解釋了。
我們?cè)賮?lái)打印看看:
$Name->show_username();
哈哈,終于打印“豬頭深空”了。不錯(cuò)吧,很方便吧,不用形參也能任意修改打印值哦~~。
不過(guò)單單打印一個(gè)名稱也太沒意思了,我們說(shuō)點(diǎn)歡迎的話吧,來(lái)擴(kuò)充一下這個(gè)類,創(chuàng)建一個(gè)名叫 Welcome 的函數(shù):
class my_class
{
??? var $username = "深空";
??? function show_username()
??? {
??????? echo $this->username;
??? }
??? function Welcome()
??? {
??? }
}
恩,實(shí)現(xiàn)什么功能好呢?簡(jiǎn)單點(diǎn)吧,就實(shí)現(xiàn)在名字前面有 “歡迎” 兩個(gè)字好了
class my_class
{
??? var $username = "深空";
??? function show_username()
??? {
??????? echo $this->username;
??? }
??? function Welcome()
??? {
??????? echo "歡迎";
??????? $this->show_username();
??? }
}
第二次看到 $this 了吧?和上次有點(diǎn)不同,$this->show_username(); 干什么用呢?指向類中的一個(gè)函數(shù),其實(shí)它就是調(diào)用 show_username 這個(gè)函數(shù),用 $this 來(lái)表示這個(gè)函數(shù)在類中并且和 Welcome 函數(shù)平行,而不是在其他地方(比如Welcome函數(shù)中)。
Welcome 函數(shù)實(shí)現(xiàn)的功能很簡(jiǎn)單,首先打印兩個(gè)字"歡迎",然后接下去執(zhí)行 show_username 函數(shù),打印名字。
來(lái)試試這個(gè)函數(shù)吧:
$Name->Welcome();
看到了吧,打印出“歡迎深空”這四個(gè)字了。
可是我要打印“歡迎豬頭深空”,怎么辦?我服了你了,我們給公共變量 var $username 一個(gè)值吧:
$Name->username = "豬頭深空";
接下去打印歡迎語(yǔ):
$Name->Welcome();
嘿嘿,終于打印“歡迎豬頭深空”了。
怎么樣?明白了類的用法了么?好處在于能夠調(diào)用類中的任意函數(shù),只要用 $this 指出來(lái),可以改變一個(gè)公共變量的值,可以在類中的函數(shù)中使用這個(gè)公共變量?!嗔巳チ?,它的應(yīng)用等待你去發(fā)現(xiàn)了。

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