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Constructor in PHP

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Release： 2024-02-28 08:24:01
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php editor Xiaoxin will give you a detailed analysis of the constructor in PHP. A constructor is a method that is automatically called when an object is instantiated to initialize the object's properties. Through the constructor, you can pass parameters and assign values ​​to properties when creating an object, improving the readability and reusability of the code. The name of the constructor is the same as the class name, and there is no need to call it manually, which facilitates unified management and maintenance of the code. In PHP, constructors are an important part of object-oriented programming. In-depth understanding and rational application of constructors can improve the quality and efficiency of code.

We will also use this function to initialize the properties of the object in the class with the given parameters.

Finally, we will see how to initiate an object in a child class and call the parent class constructor when both classes have separate constructors.

Use the php constructor to initialize the properties of the object in the class

In the following example, we will create a class Student and assign its properties to new Student using the __construct function.

The __construct function reduces the amount of code associated with using the function set_name(). 

<code>
<code class="language-php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#666"><?</span>php
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">class</span> <span style="color:#00f;font-weight:bold">Student</span> {
</span></span><span style="display:flex;"><span>	<span style="color:#408080;font-style:italic">// Define the attributes of your class
</span></span></span><span style="display:flex;"><span>	
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">public</span> <span style="color:#19177c">$name</span>;
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">public</span> <span style="color:#19177c">$em<strong class="keylink">ai</strong>l</span>;
</span></span><span style="display:flex;"><span><span style="color:#408080;font-style:italic">// Initialize the properties of the object you want to create in this class
</span></span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">funct<strong class="keylink">io</strong>n</span> __construct(<span style="color:#19177c">$name</span>, <span style="color:#19177c">$email</span>) {
</span></span><span style="display:flex;"><span>	<span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">name</span> <span style="color:#666">=</span> <span style="color:#19177c">$name</span>;
</span></span><span style="display:flex;"><span>	<span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">email</span> <span style="color:#666">=</span> <span style="color:#19177c">$email</span>;
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">function</span> <span style="color:#00f">get_name</span>() {
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">return</span> <span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">name</span>;
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">function</span> <span style="color:#00f">get_email</span>() {
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">return</span> <span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">email</span>;
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span><span style="color:#19177c">$obj</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> Student(<span style="color:#ba2121">"John"</span>, <span style="color:#ba2121">"john567@gmail.com"</span>);
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> <span style="color:#19177c">$obj</span><span style="color:#666">-></span><span style="color:#7d9029">get_name</span>();
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> <span style="color:#ba2121">"<br>"</span>;
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> <span style="color:#19177c">$obj</span><span style="color:#666">-></span><span style="color:#7d9029">get_email</span>();
</span></span><span style="display:flex;"><span><span style="color:#bc7a00">?></span><span >
</span></span></span></code></code>
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Output: 

<code>
<code class="language-text hljs" data-lang="text"><span style="display:flex;"><span>John
</span></span><span style="display:flex;"><span>john567@gmail.com
</span></span></code></code>
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Initialize properties of Object with Parameters in a class using the PHP constructor

In the example code below, we create class Military and use the __construct function to provide the properties and parameters of the object we create. 

<code>
<code class="language-php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#666"><?</span>php
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">class</span> <span style="color:#00f;font-weight:bold">Military</span> {
</span></span><span style="display:flex;"><span>	<span style="color:#408080;font-style:italic">// Define the attributes of the class &#39;Military&#39;
</span></span></span><span style="display:flex;"><span>	
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">public</span> <span style="color:#19177c">$name</span>;
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">public</span> <span style="color:#19177c">$rank</span>;
</span></span><span style="display:flex;"><span>	
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">function</span> __construct(<span style="color:#19177c">$name</span>, <span style="color:#19177c">$rank</span>){
</span></span><span style="display:flex;"><span>		<span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">name</span> <span style="color:#666">=</span> <span style="color:#19177c">$name</span>;
</span></span><span style="display:flex;"><span>		<span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">rank</span> <span style="color:#666">=</span> <span style="color:#19177c">$rank</span>;
</span></span><span style="display:flex;"><span>	}
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">function</span> <span style="color:#00f">show_detail</span>() {
</span></span><span style="display:flex;"><span>		<span style="color:#008000;font-weight:bold">echo</span> <span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">name</span><span style="color:#666">.</span><span style="color:#ba2121">" : "</span>;
</span></span><span style="display:flex;"><span>		<span style="color:#008000;font-weight:bold">echo</span> <span style="color:#ba2121">"Your Rank is "</span><span style="color:#666">.</span><span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">rank</span><span style="color:#666">.</span><span style="color:#ba2121">"</span><span style="color:#b62;font-weight:bold">\n</span><span style="color:#ba2121">"</span>;
</span></span><span style="display:flex;"><span>	}
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span><span style="color:#19177c">$person_obj</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> Military(<span style="color:#ba2121">"Michael"</span>, <span style="color:#ba2121">"General"</span>);
</span></span><span style="display:flex;"><span><span style="color:#19177c">$person_obj</span><span style="color:#666">-></span><span style="color:#7d9029">show_detail</span>();
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> <span style="color:#ba2121">"<br>"</span>;
</span></span><span style="display:flex;"><span><span style="color:#19177c">$person2</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> Military(<span style="color:#ba2121">"Fred"</span>, <span style="color:#ba2121">"Commander"</span>);
</span></span><span style="display:flex;"><span><span style="color:#19177c">$person2</span><span style="color:#666">-></span><span style="color:#7d9029">show_detail</span>();
</span></span><span style="display:flex;"><span><span style="color:#bc7a00">?></span><span >
</span></span></span></code></code>
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Output: 

<code>
<code class="language-text hljs" data-lang="text"><span style="display:flex;"><span>Michael : Your Rank is General
</span></span><span style="display:flex;"><span>Fred : Your Rank is Commander
</span></span></code></code>
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Initiating an object in a child class and calling the parent class constructor when both classes have Individual

constructors in PHP 
<code>
<code class="language-php hljs" data-lang="php"><span style="display:flex;"><span><span style="color:#666"><?</span>php
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">class</span> <span style="color:#00f;font-weight:bold">Student</span>
</span></span><span style="display:flex;"><span>{
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">public</span> <span style="color:#19177c">$name</span>;
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">public</span> <span style="color:#008000;font-weight:bold">function</span> __construct(<span style="color:#19177c">$name</span>)
</span></span><span style="display:flex;"><span>	{
</span></span><span style="display:flex;"><span>		<span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">name</span> <span style="color:#666">=</span> <span style="color:#19177c">$name</span>;
</span></span><span style="display:flex;"><span>	}
</span></span><span style="display:flex;"><span>}<span style="color:#008000;font-weight:bold">class</span> <span style="color:#00f;font-weight:bold">Identity</span> <span style="color:#008000;font-weight:bold">extends</span> Student
</span></span><span style="display:flex;"><span>{
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">public</span> <span style="color:#19177c">$identity_id</span>;
</span></span><span style="display:flex;"><span>	
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">public</span> <span style="color:#008000;font-weight:bold">function</span> __construct(<span style="color:#19177c">$name</span>, <span style="color:#19177c">$identity_id</span>)
</span></span><span style="display:flex;"><span>	{
</span></span><span style="display:flex;"><span>		<span style="color:#008000;font-weight:bold">parent</span><span style="color:#666">::</span><span style="color:#7d9029">__construct</span>(<span style="color:#19177c">$name</span>);
</span></span><span style="display:flex;"><span>		<span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">identity_id</span> <span style="color:#666">=</span> <span style="color:#19177c">$identity_id</span>;
</span></span><span style="display:flex;"><span>	}
</span></span><span style="display:flex;"><span>	<span style="color:#008000;font-weight:bold">function</span> <span style="color:#00f">show_detail</span>() {
</span></span><span style="display:flex;"><span>		<span style="color:#008000;font-weight:bold">echo</span> <span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">name</span><span style="color:#666">.</span><span style="color:#ba2121">" : "</span>;
</span></span><span style="display:flex;"><span>		<span style="color:#008000;font-weight:bold">echo</span> <span style="color:#ba2121">"Your Id Number is "</span><span style="color:#666">.</span><span style="color:#19177c">$this</span><span style="color:#666">-></span><span style="color:#7d9029">identity_id</span><span style="color:#666">.</span><span style="color:#ba2121">"</span><span style="color:#b62;font-weight:bold">\n</span><span style="color:#ba2121">"</span>;
</span></span><span style="display:flex;"><span>	}
</span></span><span style="display:flex;"><span>}
</span></span><span style="display:flex;"><span><span style="color:#19177c">$obj</span> <span style="color:#666">=</span> <span style="color:#008000;font-weight:bold">new</span> Identity(<span style="color:#ba2121">'Alice'</span>, <span style="color:#ba2121">'1036398'</span>);
</span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold">echo</span> <span style="color:#19177c">$obj</span><span style="color:#666">-></span><span style="color:#7d9029">show_detail</span>();
</span></span><span style="display:flex;"><span><span style="color:#bc7a00">?></span><span >
</span></span></span></code></code>
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Output: 

<code>
<code class="language-text hljs" data-lang="text"><span style="display:flex;"><span>Alice : Your Id Number is 1036398
</span></span></code></code>
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The Identity class extends the Student class in the above code. We use the keyword parent: to call the constructor of the Student class.

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