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Detailed explanation of classes and objects (inheritance) in php_php examples
Detailed explanation of classes and objects (inheritance) in php_php examples
在php中，类型的继承使用extends关键字，而且最多只能继承一个父类，php不支持多继承。这篇文章主要介绍了php中的类与对象(继承),需要的朋友可以参考下
简介
在php中，类型的继承使用extends关键字，而且最多只能继承一个父类，php不支持多继承。
class MyClass
{
public $dat = 0;
public function construct($dat) {
$this->dat = $dat;
}
public function getDat() {
return "$this->dat\n";
}
}
class MySubClass extends MyClass
{
public function getDat() {
return "dat: $this->dat\n";
}
}
$a = new MyClass(3);
$b = new MySubClass(4);
echo $a->getDat(); // 3
echo $b->getDat(); // dat: 4方法覆盖
包括构造函数在内，子类可以重新定义同名的类方法以覆盖父类方法。覆盖时遵循以下规则：
1.除构造函数之外，其他函数在覆盖时，函数的参数列表必须相同
2.包括构造函数在内，方法被覆盖后，调用子类方法时并不会自动调用父类方法
3.如果父类要禁止方法被子类覆盖，可以使用final来声明方法，这时如果子类仍要覆盖父类方法，将会出错
class MyClass
{
private $name = "";
public $num = 0;
public $str = "";
public function construct($name) {
$this->name = $name;
$this->num = 100;
$this->str = "none";
}
public function getName() {
return $this->name;
}
}
class MySubClass extends MyClass
{
public function construct($name, $str) {
parent::construct($name); // 调用父类方法
$this->num = "0";
$this->str = $str;
echo parent::getName()."\n"; // 调用父类方法
}
public function getName() {
return parent::getName()."$this->str\n"; // 调用父类方法
}
}
$b = new MySubClass("myName", true); // myName
echo $b->getName(); // myName1
class MyClass
{
final public function getName() {
}
}属性重定义
在子类中，可以访问父类中的public和protected属性成员，除非重定义了同名的自有属性，这时，父类中的属性将无法访问。
方法则不同，子类对方法进行覆盖后，仍然可以访问到父类方法。
class MyClass
{
public $a = 1;
protected $b = 2;
private $c = 3;
public function f1() {
echo "MyClass f1\n";
echo "\$a:$this->a; \$b:$this->b; \$c:$this->c;\n";
}
protected function f2() {
echo "MyClass f2\n";
echo "\$a:$this->a; \$b:$this->b; \$c:$this->c;\n";
}
private function f3() {
echo "MyClass f3\n";
}
}
class MySubClass extends MyClass
{
public $b = 22;
public $c = 33;
public function f1() {
echo "MySubClass f1\n";
// 继承到父类中的$a属性，直接使用
echo "\$a:$this->a; \$b:$this->b; \$c:$this->c;\n";
// 调用父类中的同名方法
parent::f1();
// 继承到父类中的f2()方法，直接使用
$this->f2();
}
// 父类的f3()是私有的，这里的定义与父类无关
public function f3() {
echo "MySubClass f3\n";
}
}
$b = new MySubClass;
$b->f1();echo "\n";
/*
MySubClass f1
$a:1; $b:22; $c:33;
MyClass f1
$a:1; $b:22; $c:3;
MyClass f2
$a:1; $b:22; $c:3;
*/
$b->f3();echo "\n";
/*
MySubClass f3
*/重定义父类(同名)属性时，属性的可访问性可以变得更开放，但不能更严格，也就是说，父类中的public属性，不能在子类中修改为private属性。
如果通过子类对象调用父类方法，那么该父类方法在访问属性时，对于重定义了的同名属性，public和protected的属性将访问到子类版本，private属性将访问到父类版本。也可以理解为，public和protected属性可以被重定义(父类的版本被重定义，从而不存在了)，而private并未被重定义(父类中的属性仍然存在，通过父类方法进行访问，与子类中是否有同名属性毫不相干)。
class MyClass
{
public $a = 1;
protected $b = 2;
private $c = 3;
public function f1() {
echo "\$a:$this->a; \$b:$this->b; \$c:$this->c;\n";
}
}
class MySubClass extends MyClass
{
public $a = 11; // 必须为public
protected $b = 22; // 必须为protected或public
private $c = 33;
public function f2() {
echo "\$a:$this->a; \$b:$this->b; \$c:$this->c;\n";
}
}
$b = new MySubClass;
$b->f1(); // $a:11; $b:22; $c:3;
$b->f2(); // $a:11; $b:22; $c:33;范围解析操作符 ::
又冒号常用于访问类常量、类静态变量，也用于在方法覆盖时调用父类版本。与其搭配的还包括parent、self、static等关键字。
class MyClass
{
const Name0 = "MyClass"; // 类常量
public static $id0 = 0; // 类变量
public function put() { // 将被子类覆盖的方法
echo "MyClass put()\n";
}
}
class MySubClass extends MyClass
{
const Name1 = "MySubClass";
public static $id1 = 1;
public function put() {
parent::put(); // 调用父类版本的对象方法
echo parent::Name0 . "\n"; // 父类常量
echo parent::$id0 . "\n"; // 父类变量
echo self::Name1."\n"; // 子类常量
echo self::$id1 . "\n"; // 子类变量
echo static::Name1 . "\n"; // 子类常理
echo static::$id1 . "\n"; // 子类变量
}
}
$a = "MyClass";
$ca = new MyClass;
$cb = new MySubClass;
$cb->put();
echo MyClass::Name0 . "\n";
echo MyClass::$id0 . "\n";
echo $a::Name0 . "\n";
echo $a::$id0 . "\n";
echo $ca::Name0 . "\n";
echo $ca::$id0 . "\n";在子类中访问父类中的成员时，应避免直接使用父类类名，而应使用parent::，以免破坏父类的封装性。
final
声明为final的方法不能被子类覆盖，如果类声明为final，则此类不能被继承。
// 声明为final的类不能被继承
final class MyClass
{
private $dat;
public function construct($dat) {
$this->dat = $dat;
}
// final方法不能被覆盖，不过此类已经是final类，方法无必要在声明为final了
final public function getDat() {
return $this->dat;
}
}总结
以上所述是小编给大家介绍的php中的类与对象(继承)，希望对大家有所帮助！！
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