php – 抽象类方法声明

我刚写了这样的代码：

<?php
class test
{
// Force Extending class to define this method
abstract protected function getValue();
abstract protected function prefixValue($prefix);

// Common method
public function printOut() {
    print $this->getValue() . "n";
}
}
class testabs extends test{

public function getValue()
{

}
public function prefixValue($f)
{

}
}
$obj = new testabs();
?>

当我运行此代码时,我收到以下错误：

Fatal error: Class test contains 2 abstract methods and must therefore be declared abstract or implement the remaining methods (test::getValue,test::prefixValue) in C:wamp64wwwstudyabstract.php on line 12

我理解这个错误的第一部分.我将类测试更改为抽象,错误消失了,但是我无法理解的部分.

visibility(参见第二小节Method Visiblilty)在子类中不相同.根据您是否希望通过子类之外的代码调用方法,可以使类test中的(抽象)方法为public,或者使子类方法也受到保护.

请注意07002的第二段,其中解释了这一点：

When inheriting from an abstract class,all methods marked abstract in the parent’s class declaration must be defined by the child; additionally,these methods must be defined with the same (or a less restricted) visibility. For example,if the abstract method is defined as protected,the function implementation must be defined as either protected or public,but not private

<?php
abstract class test{
    // Force Extending class to define this method
    abstract protected function getValue();
    abstract protected function prefixValue($prefix);

    // Common method
    public function printOut() {
        print $this->getValue() . "n";
    }
}
class testabs extends test{

    protected function getValue()
    {

    }
    /**
    *   this method can be called from other methods with this class 
    *   or sub-classes,but not called directly by code outside of this       class
    **/
    protected function prefixValue($f)
    {

    }
}
$obj = new testabs();
// this method cannot be called here because its visibility is protected
$obj->prefixValues();// Fatal Error
?>

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