根据 php.net 文档:

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. Furthermore the signatures of the methods must match, i.e. the type hints and the number of required arguments must be the same. For example, if the child class defines an optional argument, where the abstract method's signature does not, there is no conflict in the signature. This also applies to constructors as of PHP 5.4. Before 5.4 constructor signatures could differ.

在 php.net 中，他们展示了以下示例:

abstract class AbstractClass
{
    // 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 ConcreteClass1 extends AbstractClass
{
    protected function getValue() {
        return "ConcreteClass1";
    }

    public function prefixValue($prefix) {
        return "{$prefix}ConcreteClass1";
    }
}

class ConcreteClass2 extends AbstractClass
{
    public function getValue() {
        return "ConcreteClass2";
    }

    public function prefixValue($prefix) {
        return "{$prefix}ConcreteClass2";
    }
}

$class1 = new ConcreteClass1;
$class1->printOut();
echo $class1->prefixValue('FOO_') ."\n";

$class2 = new ConcreteClass2;
$class2->printOut();
echo $class2->prefixValue('FOO_') ."\n";

如果我运行它，我会得到以下输出:

ConcreteClass1 FOO_ConcreteClass1 ConcreteClass2 FOO_ConcreteClass2

阅读文档，我最初的理解是“如果子类被扩展，父类通常不能访问子类的方法”，这就是我们需要抽象类的原因。但是，当我稍作调整尝试上面的相同示例，删除所有抽象(如下所示)时，我看到与前面示例完全相同的输出。因此，为什么我们需要PHP中的抽象类。我发现的唯一用例是在父类中实现接口(interface)时；如果我不将父级声明为抽象的，我会收到错误消息。是否有其他情况我必须或强烈建议使用抽象类？

//abstract
class AbstractClass
{
    // 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 ConcreteClass1 extends AbstractClass
{
    protected function getValue() {
        return "ConcreteClass1";
    }

    public function prefixValue($prefix) {
        return "{$prefix}ConcreteClass1";
    }
}

class ConcreteClass2 extends AbstractClass
{
    public function getValue() {
        return "ConcreteClass2";
    }

    public function prefixValue($prefix) {
        return "{$prefix}ConcreteClass2";
    }
}

$class1 = new ConcreteClass1;
$class1->printOut();
echo $class1->prefixValue('FOO_') ."\n";

$class2 = new ConcreteClass2;
$class2->printOut();
echo $class2->prefixValue('FOO_') ."\n";

最佳答案

如果我有一组相似的东西，比如说家具。

class Chair extends Furniture {
    // define methods to handle being sat on
}
class Table extends Furniture {
    // define methods to handle holding things up
}

等等。但“家具”是一个抽象的概念。它本身不是“椅子”和“ table ”那样的事物。因此，最好定义:

abstract class Furniture {
    // define methods that apply to all kinds of furniture
}

将类视为“事物的类型”总是一个好主意。有些是具体的，如椅子和 table ，有些是抽象的，如家具。

重点是，在您的代码中使用 new Furniture() 是没有意义的，因为家具应该是特定种类的。使用 abstract class 不允许 new Furniture() 并充当完整性检查。

关于PHP:抽象类的用例是什么，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/32620608/