I'm trying to find a way to force the user that will implement an interface or will extend a class to create several constructors. I thought that a way to do that would be to create an abstract constructor in an abstract class, but I figured out that I can't do that.
How can I solve this issue? Is there some method to force the user to create a specific constructor?
Thanks!
You can't create an abstract constructor, but here's a workaround that you can do:
Implement an abstract class with all the constructors you want the user to implement. In each of them, you will have a single statement that refers to an abstract method from this class, which implementations will be in the subclass. This way you will force the user to provide a body for the constructor, via the abstract method implementation. For example:
public abstract class MyAbstractClass {
public MyAbstractClass(int param) {
method1(param);
}
public MyAbstractClass(int param, int anotherParam) {
method2(param, anotherParam);
}
protected abstract void method1(int param);
protected abstract void method2(int param, int anotherParam);
}
In the implementation, you will be forced to provide implementation of these two methods, which can represent the bodies of the two constructors:
public class MyClass extends MyAbstractClass {
public MyClass(int param) {
super(param);
}
public MyClass(int param, int anotherParam) {
super(param, anotherParam);
}
public void method1(int param) {
//do something with the parameter
}
public void method2(int param, int anotherParam) {
//do something with the parameters
}
}
No. But, as Constructors are often substituted by factorymethods anyway, you could implement abstract factorymethods or just other patterns like the builderpattern.
No there isn't.
However you could build a unit test framework that exploits reflection to ensure that the correct constructors are present.
