英文:
Is it right to use extend and implement in the same class?
问题
interface A {
void someMethod();
}
class B implements A {
void someMethod() {
//do something
}
}
class C extends B implements A {
void someMethod() {
super.someMethod();
//do something
}
}
我在我的代码中使用了上述的设计。它运行得很好。我在这里的整个目的是使用类B的默认实现，并在类C中执行额外操作。 这是使用实现的正确方式吗？还有其他更好的设计模式可以考虑吗？
因为如果我将我的类C定义如下，仍然一切都可以正常工作。但这忽略了使用实现的整个目的（强制类C实现接口A的方法）。
class C extends B implements A {}
英文:
interface A {
void someMethod();
}
class B implements A {
void someMethod() {
//do something
}
}
class C extends B implements A {
void someMethod() {
super.someMethod();
//do something
}
}
I'm using the above design in one of my codes. It is working fine. My whole purpose here is to use the default implementation of class B and do something extra in class C. Is this the correct way to use the implementation? Is there any better design patter to be looked at?
Because If I define my class C as below, still everything works fine. But this neglects the whole purpose of using implementation (to force class C to implement methods of interface A).
class C extends B implements A {}
答案1
得分: 0
是的，在同一类上进行扩展和实现都是完全可以的。
事实上，如果你看一下 HashMap（以及许多其他类），那就正是它的做法：
public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable
英文:
Yes, it's perfectly fine to both extend and implement on the same classes.
in fact, if you'll look at HashMap (and many others), that's exactly what it does:
public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable
答案2
得分: 0
因为当您扩展B时，它会随之附带一种someMethod的实现，从而满足契约，所以它仍然能够正常工作。
英文:
It still works fine because when you extend B that comes along with an implementation of someMethod, thus fulfilling the contract.
答案3
得分: 0
请理解，class C extends B implements A 与 class C extends B 完全相等，除了快速文档说明的目的。
尝试从 class C 中移除对 someMethod() 的定义，然后看看你的代码是否能够编译。它将能够编译通过。原因是，一旦你让 C 扩展了 B，C 默认会获得在 B 中定义的所有方法，其中也包括了 someMethod() 的实现。这违背了你明确的约定的初衷。
如果你真的想要强制 C 提供对 someMethod() 的定义，那么尝试以下代码：
interface A {
void someMethod();
}
abstract class B implements A {
protected void someUtilMethod() {
//做一些通用/默认的定义
}
}
class C extends B {
void someMethod() {
someUtilMethod();
//做一些额外的操作
}
}
英文:
Please understand that
class C extends B implements A is exactly equal to class C extends B other than the quick documentation purpose.
Try removing the defination of someMethod() from class C and see if your code compiles or not. It will compile. The reason is, the moment you made C extend B, C by default gets all the methods defined in B which includes an impementation of someMethod() as well. Defying the whole purpose of your explicit contract.
If you really want to force C to give a defination of someMethod() then try the following code:
interface A {
void someMethod();
}
abstract class B implements A {
protected void someUtilMethod() {
//do common/default defination
}
}
class C extends B {
void someMethod() {
someUtilMethod();
//do extra something
}
}
专注分享java语言的经验与见解，让所有开发者获益！
评论