PHP- object-oriented (inherited)

1.12 Inheritance

1.12.1 Introduction inheritance

Inheritance makes code hierarchical
Subclass inherits properties and methods of the parent class, to achieve the reusability of code.
Use the keyword extends inheritance
Parent class and subclass are relative

grammar

class 子类 extends 父类{
}

example

<?php
//父类
class Person {
	public function show() {
		echo '这是人类<br>';
	}
}
//子类继承父类
class Student extends Person {
}
//测试
$stu=new Student;
$stu->show();			//这是人类

Implementation process:

Step One: Find Student class show (), if you call to find, can not find it to locate the parent class

Step two: Query show the Person class ()

1.12.2 subclass call the parent class members

<?php
//父类
class Person {
	public function show() {
		echo '这是人类<br>';
	}
}
//子类
class Student extends Person {
	public function test() {
		//方法一；
		/*
		$person=new Person();
		$person->show();		//这是人类
		*/
		//方法二
		$this->show();			//这是人类
	}
}
//测试
$stu=new Student;
$stu->test();

summary:

1, a method of: calling a member of the parent class's parent class by instantiating

2. Method Two: Call to a member of the parent class by $ this keyword

1.12.3 protected

protected: protected, use the entire inheritance chain

example:

//例题一：
<?php
class A {
	protected $num=10;	//在整个继承链上访问
}
class B extends A {	
	public function getNum() {
		echo $this->num;
	}
}
//测试
$obj=new B();    //整个继承链上有A和B
$obj->getNum();		//10

//例题二：
<?php
class A {
	public function getNum() {
		echo $this->num;
	}
}
class B extends A {
	protected $num=10;	
}
//测试
$obj=new B();	//整个继承链上有A和B
$obj->getNum();		//10

//例题三：
<?php
class A {
	public function getNum() {
		echo $this->num;
	}
}
class B extends A {
	protected $num=10;	
}
//测试
$obj=new A();     //整个继承链上只有A
$obj->getNum();	 //Notice: Undefined property: A::$num

1.12.4 inheritance constructor

rule:

1、如果子类有构造函数就调用子类的，如果子类没有就调用父类的构造函数。

2、子类的构造函数调用后，默认不再调用父类的构造函数

Call the constructor of the parent class by class name

类名::__construct()

example

<?php
class Person {
    //父类的构造函数
	public function __construct() {
		echo '这是父类<br>';
	}
}
class Student extends Person {
    //子类的构造函数
	public function __construct() {
		Person::__construct();		//通过父类的名字调用父类的构造函数
		parent::__construct();		//parent表示父类的名字
		echo '这是子类<br>';
	}
}
//测试
new Student();

Note: parent keyword indicates the name of the parent class, you can reduce coupling procedure

Example: passing parameters to the parent class

<?php
class Person {
	protected $name;
	protected $sex;
    //父类的构造函数
	public function __construct($name,$sex) {
		$this->name=$name;
		$this->sex=$sex;
	}
}
class Student extends Person {
	private $score;
    //子类的构造函数
	public function __construct($name,$sex,$score) {
		parent::__construct($name,$sex);  //调用父类构造函数并传递参数
		$this->score=$score;
	}
    //显示信息
	public function getInfo() {
		echo "姓名：{$this->name}<br>";
		echo "性别：{$this->sex}<br>";
		echo "成绩：{$this->score}";
	}
}
//测试
$stu=new Student('tom','男',88);
$stu->getInfo();
/*
姓名：tom
性别：男
成绩：88
*/

1.12.5 $ this Detailed

$this is a reference to the current object, that is, or is$ an address stored in this current object

<?php
class A {
	public function __construct() {
		var_dump($this);
	}
}
class B extends A {
	
}
new A();	//object(A)#1 (0) { } 
echo '<br>';
new B();	//object(B)#1 (0) { }