PHP 추상 클래스 기능 예제에 대한 자세한 설명

abstract class AbstractClass{
 // 强制要求子类定义这些方法
    abstract protected function getValue();
    abstract protected function prefixValue($prefix);

    // 普通方法（非抽象方法）
    public function printOut() {
        print $this->getValue() . "\n";
    }
class ConcreteClass1 extends AbstractClass{   //父类定义了俩个抽象方法，如子类只实现了其中一个，则报如下错误//Fatal error: Class ConcreteClass1 contains 1 abstract //method and must therefore be declared abstract or //implement the remaining methods //(AbstractClass::prefixValue)
    protected function getValue() {
        return "ConcreteClass1";
    } 
   // 且子类的访问权限不能低于父类，如果将如下子类的访问方式改为private则会报如下错误
    //Fatal error: Access level to //ConcreteClass1::prefixValue() must be protected (as in //class AbstractClass) or weaker
    public function prefixValue($prefix) {
        return "{$prefix}ConcreteClass1";
    }

}

//当实例化一个抽象类时，Fatal error: Cannot instantiate //abstract class AbstractClass
//$obj = new AbstractClass();
// 但是我们可以这么使用##########################################################
abstract class Foo{
     static function bar()
     {
         echo "test\n";
     }
 }

Foo::bar();##########################################################
$obj = new ConcreteClass1();
echo $obj->getValue();

abstract class AbstractClass{
    // 我们的抽象方法仅需要定义需要的参数
    abstract protected function prefixName($name);
}

class ConcreteClass extends AbstractClass
{

    // 我们的子类可以定义父类签名中不存在的可选参数
    // 如果这里的$separator没有默认值，则会报Fatal error: 、、//Declaration of ConcreteClass::prefixName() must be //compatible with that of AbstractClass::prefixName()
    public function prefixName($name, $separator = ".") {
        if ($name == "Pacman") {            $prefix = "Mr";
        } elseif ($name == "Pacwoman") {            $prefix = "Mrs";
        } else {            $prefix = "";
        }        return "{$prefix}{$separator} {$name}";
    }
}

$class = new ConcreteClass;
echo $class->prefixName("Pacman"), "\n";
echo $class->prefixName("Pacwoman"), "\n";

abstract class A{
     public function show(){
         echo 'A';
     }
 } class B extends A{
     public function hello(){
         echo 'B';         
         parent::show();
     }
 } 
 $obj = new B; 
 $obj->hello(); // BA

// 正确的定义顺序
abstract class horse extends animal {
     public function get_breed() { return "Jersey"; }
 } 
 class cart extends horse {
     public function get_breed() { return "Wood"; }
 }
 // 错误的定义顺序，将会导致horse类找不到
 class cart extends horse {
     public function get_breed() { return "Wood"; }
 } 
 abstract class horse extends animal {
     public function get_breed() { return "Jersey"; }
 }

abstract class FOO
{
     abstract static function dump();
 } 
 class BAR extends FOO{
     static function dump(){var_dump("BAR");}
 }
BAR::dump(); // string(3) "BAR"