PHP Study Notes 2 Introduction to PHP_PHP Tutorial

PHP Study Notes 2
1. Array
PHP’s array is actually an associative array, or a hash table. PHP does not need to declare the size of the array in advance, and can create an array by direct assignment. For example:
//The most traditional, use numbers as keys and assign values ​​
$state[0]="Beijing";
$state[1]="Hebei";
$state[2] ="Tianjin";
//If the key is an increasing number, you can omit
$city[]="Shanghai";
$city[]="Tianjin";
$city[ ]="Guangzhou";
//Use string as key
$capital["China"]="Beijing";
$capital["Japan"]="Tokyo";
Use It is more convenient to create an array with array(). You can pass array elements to it as array parameters, or you can use the => operator to create an associative array. For example:
$p=array(1,3,5,7);
$capital=array(“China”=>”Beijing”, “Japan=>”Tokyo”);
Array is actually a grammatical structure, not a function. Similar to array, there is also a list(), which can be used to extract values ​​from an array and assign values ​​to multiple variables. For example:
list($s, $t)=$city;
echo $s,' ',$t;
Output result: Shanghai Tianjin
Note that the list method can only be used in arrays indexed by numbers
PHP. We have built some commonly used array processing functions. For details, please refer to the manual. Examples of commonly used functions are as follows. count or sizeof can get the length of an array. array_merge can merge two or more arrays. array_push (pop) can use arrays like a stack. .

Copy code The code is as follows:

$state[0]="Beijing";
$state[1]="Hebei";
$state[2]="Tianjin";
$city[]="Shanghai";
$city[]="Tianjin";
$city[]="Guangzhou";
$capital["China"]="Beijing";
$capital["Japan"]="Tokyo";
echo count($city ),'
';
array_push($capital,"Paris");
$newarray=array_merge($city,$capital);
foreach($newarray as $elem)
echo $elem.'
';
?>

The output result is:
3
Shanghai
Tianjin
Guangzhou
Beijing
Tokyo
Paris
2. Classes and objects
PHP5 has begun to have good support for the concept of classes in PHP and other object-oriented languages ​​such as C# is very similar. It is also an aggregate of values ​​and methods, defined using the class keyword. For example:

Copy the code The code is as follows:

class AuthUser {
protected $userName;
protected $password;
public function __construct($userName,$password) {
$this- >userName=$userName;
$this->password=$password;
}
public function GetUserName() {
return $userName;
}
public function ChangePassword ($old,$new) {
if($this->password==$old) {
$this->password=$new;
return true;
}else
return false;
}
public function Login($password) {
return $this->password==$password;
}
public static function CreateUser($userName, $password) {
$user=new AuthUser($userName,$password);
return $user;
}
}
$user=AuthUser::CreateUser("Admin", "123");
echo $user->GetUserName();
if($user->ChangePassword('abc', 'new'))
echo 'ChangePassword success';
else
echo 'Change Password fail';
$user->ChangePassword("123", "321");
if($user->Login("321"))
echo "Login";
else
echo "Login fail";
?>

The above is a class that is useless but has a relatively complete syntax structure. First, use the class keyword to define the name of the class, and fields and methods can be defined internally. Modifiers for fields and methods can be private, protected, public and final (only methods have them). Its meaning is consistent with other languages. No more details. The difference is that PHP does not support function overloading. In addition, the definition of PHP5's constructor is __construct. Note that the prefix is ​​two underscores. The definition of the constructor of PHP4 is consistent with that of other languages. It is the same function as the class name. PHP5 is also compatible with this writing method. PHP5 also supports destructors, named __destruct. Inside a function, you can use the $this variable to get a reference to the current object. PHP also supports static functions, which are also modified using the static keyword. The last function in the example is a static function. Static functions cannot be referenced through instances of classes.
The definition of a class. The following is a code example of using a class. PHP also instantiates a class through the new keyword. Methods of objects are referenced through the -> operator. Note that the reference method of its static class is::, which is consistent with C++.
The following is a brief introduction to the inheritance of the following classes. The extends keyword is used in PHP to implement class inheritance, which is consistent with Java:

Copy code The code is as follows:

class BaseClass {
function __construct() {
print "In BaseClass constructorn";
}
}
class SubClass extends BaseClass {
function __construct() {
parent::__construct();
print "In SubClass constructorn";
}
}
$obj = new BaseClass();
$obj = new SubClass();
?>

The output result is: In BaseClass constructor In BaseClass constructor In SubClass constructor
Note that the constructor of PHP subclass The constructor of the parent class is not automatically called and must be called explicitly in the program. Use the parent keyword to get a reference to the parent class. In addition, since PHP itself is weakly typed, the concept of "polymorphism" no longer exists. In fact, it will always be polymorphic.
Interface
An interface defines a set of methods but does not implement them. The syntax is:
interface IInterfaceName
{
//Constant, function definition
} The class uses the implements keyword to superficially implement an interface, which is consistent with Java.

Copy code The code is as follows:

interface IAddable{
function Add($something );
}
class AddClass implements IAddable
{
private $data;
function AddClass($num){
$data=$num;
}
public function Add($something)
{
$data+=$something;
return $data;
}
}
$a=new AddClass (5);
echo $a instanceof IAddable;
echo $a->Add(10);
?>

The instanceof keyword is new in PHP5 and is used to determine an object Is it an instance of a certain class, or does its type implement an interface?

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