如何解决Java中缺少抽象字段的问题？ [英] How to get around the lack of abstract fields in Java?

问题描述

假设我们有一个抽象类 A ，我们想强制所有子类都有一个特定的字段。这在Java中是不可能的，因为我们无法定义抽象字段。

Assume, we have an abstract class A and we want to force all subclasses to have a certain field. This is not possible in Java, because we can not define abstract fields.

解决方法1：强制子类实现提供所需的方法值。

Workaround 1: Force subclasses to implement a method which delivers the wanted value.

abstract class A {
  abstract int getA();
}

缺点：每个子类都必须实现一个方法对于我们想要的每个抽象字段。这可以导致许多方法实现。

Drawback: Each subclass has to implement a method for each abstract field we want to have. This can lead to many method implementations.

Advantage ：我们可以使用方法 getA 在抽象类中实现方法，并在 A 中实现它们，而不在每个子类中实现它们。但是方法背后的价值不能被抽象类覆盖。

Advantage: We can use the method getA in the abstract class and implement methods with it in A without implementing them in each subclass. But the value behind the method can not be overwritten by the abstract class.

解决方法2：通过强制子类给出来模拟抽象字段抽象类一个值。

Workaround 2: Simulate the abstract field by forcing the subclass to give the abstract class a value.

abstract class A {
  int a;

  public A(int a) {
    this.a = a;
  }
}

缺点：当我们有多个字段（> 10），超级构造函数调用看起来有点难看和混乱。

Drawback: When we have multiple fields (> 10), the super constructor call will look a bit ugly and confusing.

Advantage ：我们可以使用字段<抽象类中的code> a ，并在 A 中实现方法，而不在每个子类中实现它们。另外，值 a 可以被抽象类覆盖。

Advantage: We can use the field a in the abstract class and implement methods with it in A without implementing them in each subclass. Plus, the value a can be overwritten by the abstract class.

问题：哪种解决方法是实现目标的常用方法？也许有一个比上面的更好？

Question: Which workaround is the common way to reach the goal ? Maybe there is a better one than the above ones ?

推荐答案

抽象方法可能是最面向对象的。

The abstract method is probably the most object oriented.

如果你有太多的字段，你可能想要重新组合POJO（如果一个新的概念是合适的）。

If you have too many fields, you may want to regroup those in a POJO (if a new concept is appropriate).

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