Java 中是否可以混合组合和继承?首先,我有一些通用类是 HAS-A(或 HAS-MANY)关系(组合)。
通用类:
Structure、TypeA、TypeB、TypeC 等,其中 Structure 与 TypeA、TypeB 和 TypeC 是 HAS-A 关系。
但是我也有几组子类,它们从泛型类继承(继承)并且具有相同的关系。
子类集:
设置 1:
Structure1、TypeA1、TypeB1、TypeC1 等,其中 Structure1 与 TypeA1、TypeB1 和 TypeC1 具有相同的 HAS-A 关系,就像泛型类一样。
并且:Structure1 扩展 Structure,TypeA1 扩展 TypeA,...,TypeC1 扩展 TypeC,等等
...直到设置 X:
StructureX、TypeAX、TypeBX、TypeCX 等
每个特殊结构都有一个特定的子类型A、子类型B和子类型C等。通用类定义了一些我希望在处理特殊结构时重用的代码(属性和方法)。 下面的代码可以最好地解释我面临的问题。 (我不知道这是否可以通过 Java“泛型”以某种方式解决,但我认为不能。)
/***********************************************************************************************
/ Generic Structure of Structure-Class with Instances of Generic other classes (Composition)
/***********************************************************************************************/
class Structure {
// Substructures
TypeA instanceA;
TypeB instanceB;
// Defining many methods using the instances of other generic classes like TypeA
void setGenericAttributeOfA(int value) {
instanceA.genericAttribute = value;
}
void setGenericAttributeOfB(int value) {
instanceB.genericAttribute = value;
}
}
class TypeA {
int genericAttribute;
}
class TypeB {
int genericAttribute;
}
/***********************************************************************************************
/ Specific implementation of a Structure-Class with specific implementation of the other classes (Inheritance)
/***********************************************************************************************/
// In the specific implementations I want to use the generic methods, because I do not want to
// rewrite the code for each and every specific implementation. But they should
class Structure1 extends Structure {
// This will create an additional attribute instanceA of specific TypeA1, so I will end up with two instances:
// (1) TypeA super.instanceA and (2) TypeA1 this.instanceA. But what I would like is to have only
// one instanceA of type TypeA1 that can also be used by the global methods of the generic Structure.
TypeA1 instanceA;
Structure1() {
// This creates an instance of type TypeA1, but it cannot be used in the generic methods
// because it is hold in a separate "local" variable that is not known to the generic Structure methods
instanceA = new TypeA1();
// This creates an instance of type TypeB1, but it cannot access the "local" specific attributes,
// because it is hold in a varable which is statically types as TypeB
instanceB = new TypeB1();
}
void specificMethod() {
setGenericAttributeOfA(42); // would fail, because instanceA of type generic TypeA is null
instanceA.specificAttribute = 13; // works only for "local" specific attributes
setGenericAttributeOfB(42); // works only for generic attributes
instanceB.specificAttribute = 13; // would fail, because instanceB is statically typed as generic TypeB which does not have this attribute
((TypeB1)instanceB).specificAttribute = 13; // works but is an ugly work-around and over-complicated if to be used many times
}
}
class TypeA1 extends TypeA {
int specificAttribute;
}
class TypeB1 extends TypeB {
int specificAttribute;
}
最佳答案
也许Generics可以帮忙吗?
将结构
声明为通用:
class Structure<T1 extends TypeA, T2 extends TypeB, T3 extends TypeC> {
T1 instanceA;
T2 instanceB;
T3 instanceC;
}
并且您的特定结构将通过指定类型参数从通用 Structure
继承:
class Structure1 extends Structure<TypeA1, TypeB1, TypeC1> {
// here instanceA will be of type TypeA1, instanceB will be TypeB1 etc.
}
关于java - 在 Java 中混合组合和继承,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/50048195/