时间：2021-07-01 10:21:17 帮助过：3人阅读
1. __construct:
内置构造函数，在对象被创建时自动调用。见如下代码：
<?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");
$testObject->printAttributes();运行结果如下：
Stephens-Air:Desktop$ php Test.php __construct is called... $arg1 = arg1 $arg2 = arg2
2. parent:
用于在子类中直接调用父类中的方法，功能等同于Java中的super。
<?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 $testObject->getAttributes()."\n";运行结果如下：
Stephens-Air:Desktop$ php Test.php __construct is called... $arg1 = arg1 $arg2 = arg2 $arg3 = arg3
3. self:
在类内调用该类静态成员和静态方法的前缀修饰，对于非静态成员变量和函数则使用this。
<?php
class StaticExample {
static public $arg1 = "Hello, This is static field.\n";
static public function sayHello() {
print self::$arg1;
}
}
print StaticExample::$arg1;
StaticExample::sayHello();运行结果如下：
Stephens-Air:Desktop$ php Test.php Hello, This is static field. Hello, This is static field.
4. static:
这里介绍的static关键字主要用于PHP 5.3以上版本新增的延迟静态绑定功能。请看一下代码和关键性注释。
<?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();运行结果如下：
Stephens-Air:Desktop$ php Test.php This is SubA::printSelf. This is SubB::printSelf.
static关键字不仅仅可以用于实例化。和self和parent一样，static还可以作为静态方法调用的标识符，甚至是从非静态上下文中调用。在该场景下，self仍然表示的是当前方法所在的类。见如下代码：
<?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();运行结果如下：
Stephens-Air:Desktop$ php Test.php My Group is default My Group is SubB
5. __destruct:
析构方法的作用和构造方法__construct刚好相反，它只是在对象被垃圾收集器收集之前自动调用，我们可以利用该方法做一些必要的清理工作。
<?php
class TestClass {
function __destruct() {
print "TestClass destructor is called.\n";
}
}
$testObj = new TestClass();
unset($testObj);
print "Application will exit.\n";运行结果如下：
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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