为什么Java中同一个类中不能有抽象方法和静态方法

发布于 2024-12-25 16:15:28 字数 400 浏览 1 评论 0原文

我有以下课程：

public abstract class A
{
  public abstract String doSomething(String X, String Y);
  public static String doSomething(String X, String Y){return X + Y;}
  ...
}

我遇到的问题是静态和抽象 doSomething() 方法似乎因重复而发生冲突。我认为这应该没问题，因为静态方法属于类，而不是类的实例，所以我打算使用抽象方法在所有子类上强制执行该方法，并将静态方法作为辅助方法，这样我就可以很好地因式分解的代码。

我知道我可能可以在组合中添加一个接口，但我真的不明白同一个类上存在的抽象方法和静态方法有什么问题。这有什么问题吗？

原文

I have the following class:

public abstract class A
{
  public abstract String doSomething(String X, String Y);
  public static String doSomething(String X, String Y){return X + Y;}
  ...
}

The issue I have is that the static and abstract doSomething() methods seem to clash as duplicates. I thought this should be fine because the static method belongs to the class, not an instance of the class, so I was going to use the abstract method to enforce the method on all subclasses and the static method as a helper so that I have nicely factored code.

I know I could probably add an interface into the mix, but I don't really understand what's wrong with my abstract and static methods existing on the same class. What's wrong with this?

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幽蝶幻影 2025-01-01 16:15:28

在 Java 中，从对象实例而不是类名调用静态方法是有效的（尽管会产生误导和混淆）（尽管许多编译器会生成警告）。

System.out.println(String.valueOf(true)); // Prints "true".
System.out.println("".valueOf(true)); // Prints "true", unfortunately.

因此，以下看似有效的代码将不知道要调用这些方法中的哪一个：

A a = getInstanceOfConcreteSubclassOfA();
a.doSomething(null, null); // Compiler can't decide which method to call...

不幸的是，它只是 Java 语言中为数不多的丑陋角落之一。

In Java it is valid (despite being misleading and confusing) to call a static method from an object instance rather than the class name (despite warnings generated by many compilers).

System.out.println(String.valueOf(true)); // Prints "true".
System.out.println("".valueOf(true)); // Prints "true", unfortunately.

So the following seemingly valid code wouldn't know which of those methods to call:

A a = getInstanceOfConcreteSubclassOfA();
a.doSomething(null, null); // Compiler can't decide which method to call...

Unfortunately, it's just one of the few ugly corners of the Java language.

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等你爱我 2025-01-01 16:15:28

它并不特定于抽象方法；一般来说，Java 不允许您拥有两种具有相同参数类型的方法，但一种是静态的，另一种不是。像这样的事情：

public String doSomething(String X, String Y){return X + Y;}
public static String doSomething(String X, String Y){return X + Y;}

也是非法的。

（当您认为您可以在实际实例“上”调用静态方法，或者就此而言，在适当类型的任何表达式上调用静态方法时，这是有意义的。编译器会翻译 ((A)null)。 staticMethod() 到 A.staticMethod()。）

It's not specific to abstract methods; in general, Java doesn't let you have two methods with the same parameter-types but one being static and one not. Something like this:

public String doSomething(String X, String Y){return X + Y;}
public static String doSomething(String X, String Y){return X + Y;}

would also be illegal.

(This makes sense when you consider that you're allowed to call a static method "on" an actual instance, or for that matter, on any expression of the appropriate type. The compiler translates ((A)null).staticMethod() to A.staticMethod().)

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