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This article mainly introduces some knowledge points about PHP object-oriented, which has certain reference value. Now I share it with everyone. Friends in need can refer to it
1. __construct:
Built-in constructor, automatically called when the object is created. See the following code:
<?php class ConstructTest { private $arg1; private $arg2; public function __construct($arg1, $arg2) { $this->arg1 = $arg1; $this->arg2 = $arg2; print "__construct is called...\n"; } public function printAttributes() { print '$arg1 = '.$this->arg1.' $arg2 = '.$this->arg2."\n"; } } $testObject = new ConstructTest("arg1","arg2"); $testObject->printAttributes();
The running results are as follows:
Stephens-Air:Desktop$ php Test.php __construct is called... $arg1 = arg1 $arg2 = arg2
2. parent:
Used to directly call the parent class in the subclass Method, function is equivalent to super in Java.
<?php class BaseClass { protected $arg1; protected $arg2; function __construct($arg1, $arg2) { $this->arg1 = $arg1; $this->arg2 = $arg2; print "__construct is called...\n"; } function getAttributes() { return '$arg1 = '.$this->arg1.' $arg2 = '.$this->arg2; } } class SubClass extends BaseClass { protected $arg3; function __construct($baseArg1, $baseArg2, $subArg3) { parent::__construct($baseArg1, $baseArg2); $this->arg3 = $subArg3; } function getAttributes() { return parent::getAttributes().' $arg3 = '.$this->arg3; } } $testObject = new SubClass("arg1","arg2","arg3"); print $testObject->getAttributes()."\n";
The running results are as follows:
Stephens-Air:Desktop$ php Test.php __construct is called... $arg1 = arg1 $arg2 = arg2 $arg3 = arg3
3. self:
Call the prefix modification of the static members and static methods of the class within the class, for Non-static member variables and functions use this.
<?php class StaticExample { static public $arg1 = "Hello, This is static field.\n"; static public function sayHello() { print self::$arg1; } } print StaticExample::$arg1; StaticExample::sayHello();
The running results are as follows:
Stephens-Air:Desktop$ php Test.php Hello, This is static field. Hello, This is static field.
4. static:
The static keyword introduced here is mainly used for PHP 5.3 or above. Delayed static binding functionality. Please take a look at the code and critical comments.
<?php abstract class Base { public static function getInstance() { //这里的new static()实例化的是调用该静态方法的当前类。 return new static(); } abstract public function printSelf(); } class SubA extends Base { public function printSelf() { print "This is SubA::printSelf.\n"; } } class SubB extends Base { public function printSelf() { print "This is SubB::printSelf.\n"; } } SubA::getInstance()->printSelf(); SubB::getInstance()->printSelf();
The running results are as follows:
Stephens-Air:Desktop$ php Test.php This is SubA::printSelf. This is SubB::printSelf.
The static keyword can not only be used for instantiation. Like self and parent, static can also be used as an identifier for static method calls, even from non-static contexts. In this scenario, self still represents the class where the current method is located. See the following code:
<?php abstract class Base { private $ownedGroup; public function __construct() { //这里的static和上面的例子一样,表示当前调用该方法的实际类。 //需要另外说明的是,这里的getGroup方法即便不是静态方法,也会得到相同的结果。然而倘若 //getGroup真的只是普通类方法,那么这里还是建议使用$this。 $this->ownedGroup = static::getGroup(); } public function printGroup() { print "My Group is ".$this->ownedGroup."\n"; } public static function getInstance() { return new static(); } public static function getGroup() { return "default"; } } class SubA extends Base { } class SubB extends Base { public static function getGroup() { return "SubB"; } } SubA::getInstance()->printGroup(); SubB::getInstance()->printGroup();
The running result is as follows:
Stephens-Air:Desktop$ php Test.php My Group is default My Group is SubB
5. __destruct:
The function of the destructor method and The constructor method __construct is just the opposite. It is only called automatically before the object is collected by the garbage collector. We can use this method to do some necessary cleanup work.
<?php class TestClass { function __destruct() { print "TestClass destructor is called.\n"; } } $testObj = new TestClass(); unset($testObj); print "Application will exit.\n";
The running results are as follows:
Stephens-Air:Desktop$ php Test.php TestClass destructor is called. Application will exit.
6. __clone:
在PHP 5之后的版本中,对象之间的赋值为引用赋值,即赋值后的两个对象将指向同一地址空间,如果想基于对象赋值,可以使用PHP提供的clone方法。该方法将当前对象浅拷贝之后的副本返回,如果想在clone的过程中完成一些特殊的操作,如深拷贝,则需要在当前类的声明中实现__clone方法,该方法在执行clone的过程中会被隐式调用。另外需要格外注意的是,__clone方法是作用再被拷贝的对象上,即赋值后的对象上执行。
<?php class InnerClass { public $id = 10; public function printSelf() { print '$id = '.$this->id."\n"; } } class OuterClass { public $innerClass; public function __construct() { $this->innerClass = new InnerClass(); } public function __clone() { $this->innerClass = clone $this->innerClass; print "__clone is called.\n"; } } $outerA = new OuterClass(); print "Before calling to clone.\n"; $outerB = clone $outerA; print "After calling to clone.\n"; $outerA->innerClass->id = 20; print "In outerA: "; $outerA->innerClass->printSelf(); print "In outerB: "; $outerB->innerClass->printSelf();
运行结果如下:
Stephens-Air:Desktop$ php Test.php Before calling to clone. __clone is called. After calling to clone. In outerA: $id = 20 In outerB: $id = 10
7. const:
PHP5可以在类中定义常量属性。和全局常量一样,一旦定义就不能改变。常量属性不需要像普通属性那样以$开头,按照惯例,只能用大写字母来命名常量。另外和静态属性一样,只能通过类而不能通过类的实例访问常量属性,引用常量时同样也不需要以$符号作为前导符。另外常量只能被赋值为基础类型,如整型,而不能指向任何对象类型。
<?php class TestClass { const AVAILABLE = 0; } print "TestClass::AVAILABLE = ".TestClass::AVAILABLE."\n";
运行结果如下:
0Stephens-Air:Desktop$ php Test.php TestClass::AVAILABLE = 0
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