[英]Class Hierarchy design for optional attribute
At the moment my application has the following class hierarchy: 目前,我的应用程序具有以下类层次结构:
At the moment, "Class A" has an attribute called "Attribute D" which is mandatory for "Class B" but optional in "Class C". 目前,“A类”具有称为“属性D”的属性,对于“B类”是强制性的,但在“C类”中是可选的。
May I know the best way to represent this data structure? 我可以知道表示此数据结构的最佳方法吗? such that rather than letting others referencing ClassA.getAttributeD without checking if it is NULL, we force them to use Class B and Class C to reference the field
这样,我们强制他们使用Class B和Class C引用该字段,而不是让其他人引用ClassA.getAttributeD而不检查它是否为NULL。
Add a constructor in Class B
with Attribute D
. 使用
Attribute D
在Class B
添加构造函数。 In Class C
there is just a setter for this attribute. 在
Class C
,只有这个属性的setter。
abstract class A {
Object attributeD;
void setAttributeD(Object attributeD) { this.attributeD = attributeD; }
Object getAttributeD() { return attributeD; }
}
class B extends A {
B(Object attributeD) { this.attributeD = attributeD; }
}
class C extends A {
}
Don't overuse inheritance. 不要过度使用继承。 Often it makes things more complicated as necessary.
通常它会使事情变得更加复杂。 You can see this already in your question.
您可以在问题中看到这一点。
Take a look at this: 看看这个:
Class A {
private int d = 1;
protected int getD() {
return d;
}
}
Class B extends A {
public void doStuff() {
B b = new B();
System.out.println(b.getD());
}
}
Class C extends A {
public void doStuff() {
C c = new C();
System.out.println(c.getD());
}
}
Your main problem is to avoid users accessing attribute D
. 您的主要问题是避免用户访问
attribute D
You can do so by setting attribute D
to be private, then declare protected methods to access the attribute. 您可以通过将
attribute D
设置为私有来执行此操作,然后声明受保护的方法以访问该属性。 This way, the subclasses will be able to access the attribute. 这样,子类就能够访问该属性。
Make the field in A protected, or keep it private and make its accessor protected. 使A中的字段受到保护,或将其保密,并使其访问者受到保护。
Thus, users of the class A cannot access the field, but class B and C can use it, and can make accessors public for it. 因此,A类用户无法访问该字段,但B类和C类可以使用它,并且可以为其公开访问者。
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