相关疑难解决方法(0)

由于只有狗可以玩"获取",这个例子是好还是坏？由于使用了instanceof,我怀疑这是一个非常糟糕的主意,但我不完全确定原因.

class Animal {
    var $name;
    function __construct($name) {
        $this->name = $name;
    }
}

class Dog extends Animal {
    function speak() {
        return "Woof, woof!";
    }

    function playFetch() {
        return 'getting the stick';
    }
}

class Cat extends Animal {
    function speak() {
        return "Meow...";
    }
}

$animals = array(new Dog('Skip'), new Cat('Snowball'));

foreach($animals as $animal) {
    print $animal->name . " says: " . $animal->speak() . '<br>';
    if ($animal instanceof Dog) echo $animal->playFetch();
}

另一个例子.由于我不断创建具有ID的数据对象,我想我也可以从基类扩展它们以避免代码重复.再次,这是不对的？由于椅子没有名字,狗没有轮子.但它们都是数据对象,因此非常令人困惑.

class Data_Object { …

Alrite,我会直接跳到代码:

public interface Visitor {

public void visitInventory(); 
public void visitMaxCount();
public void visitCountry();
public void visitSomethingElse();
public void complete();
//the idea of this visitor is that when a validator would visit it, it would validate data
//when a persister visits it, it would persist data, etc, etc.
// not sure if I making sense here...
}

public interface Visitable {
public void accept(Visitor visitor); 
}

这是一个基础实现:

public class StoreValidator implements Visitor {
private List <ValidationError> storeValidationErrors = new ArrayList<ValidationError>(); …

以下是使用泛型的访问者模式的java实现,一般是否有用？(我想是的).

它能以某种方式得到改善吗？使用匿名类轻松调用很重要.谢谢.

(使用示例):

Vector<Number> numbers = new Vector<Number>();

        numbers.add(new Double(1.2));
        numbers.add(new Float(-1.2));
        numbers.add(new Double(4.8));
        numbers.add(new Float(-3.4));
        numbers.add(new Long(123456));
        numbers.add(new Short("14"));

        For.each(numbers, new Visitor<Number>() {
            public void doIt(Double n) {
                System.out.println("doIt() for double: " + n);
            }
            public void doIt(Float n) {
                System.out.println("doIt() for float: " + n);
            }
            public void doIt(Number n) {
                System.out.println("doIt() for Number: " + n);
            }
        });

        Visitor<Number> visi =  new Visitor<Number>() {
            private StringBuffer  all = new StringBuffer ();
            public void doIt(Number n) {
                System.out.println("doIt() …