在 Java 中使用私有默认构造函数子类化 class

Question

Say I have class A with a private constructor, and class B that extends it:

public class A {
    private A() {}
}

public class B extends A {
    public B(){
        // error - there is no default constructor available in 'A'
    }
}

I know it is possible to call private constructors via Java Reflection, but how can I do it in the B constructor ? Thanks.

Answer 1

If class B extends A and A 's constructor is private, subclassing is not possible unless both classes are defined in the same file as inner classes (see Preventing Instantiation of a Class ). That's because the constructor of the subclass does an (either explicit or implicit) super() call. A super() call is basically just a call to the matching constructor and if that constructor is declared private , this call is not possible from some outer class (eg one defined in a different file).