如何解决 Java 中缺少抽象字段的问题?

问题描述

假设，我们有一个抽象类 A 并且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，因为我们不能定义抽象字段.

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价值的方法.

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

abstract class A {
  abstract int getA();
}

缺点:每个子类都必须为我们想要的每个抽象字段实现一个方法.这会导致许多方法实现.

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

优点:我们可以在抽象类中使用方法getA，并在A中使用它来实现方法，而无需在每个子类中实现它们.但是方法后面的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: 通过强制子类为抽象类提供值来模拟抽象字段.

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)时，超级构造函数调用会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.

优点:我们可以在抽象类中使用字段a，并在A中使用它来实现方法，而无需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?也许有比上面更好的?

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.

如果您有太多字段，您可能需要在 POJO 中重新组合这些字段(如果新概念合适).

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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