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# Constructors and Destructors

## Constructor

PHP 5 allows developers to declare constructor methods for classes. Classes which have a constructor method call this method on each newly-created object, so it is suitable for any initialization that the object may need before it is used.

> 備注: Parent constructors are not called implicitly. In order to run a parent constructor, a call to parent::__construct() is required.

示範 14-1.using new unified constructors

`<?php class BaseClass { function __construct() { print "In BaseClass constructor\n"; } } class SubClass extends BaseClass { function __construct() { parent::__construct(); print "In SubClass constructor\n"; } } $obj = new BaseClass(); $obj = new SubClass(); ?>`

For backwards compatibility, if PHP 5 cannot find a __construct() function for a given class, it will search for the old-style constructor function, by the name of the class. Effectively, it means that the only case that would have compatibility issues is if the class had a method named __construct() which was used for different semantics.

## Destructor

PHP 5 introduces a destructor concept similar to that of other object-oriented languages, such as Java: When the last reference to an object is destroyed the object's destructor, which is a class method named __destruct() that receives no parameters, is called before the object is freed from memory.

示範 14-2.Destructor Example

`<?php class MyDestructableClass { function __construct() { print "In constructor\n"; $this->name = "MyDestructableClass"; } function __destruct() { print "Destroying " . $this->name . "\n"; } } $obj = new MyDestructableClass(); ?>`

Like constructors, parent destructors will not be called implicitly by the engine. In order to run a parent destructor, one would have to explicitly call parent::__destruct() in the destructor body.

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