Java子类中的构造函数不正确

Question

Can someone please help me understand why (in Java) class B is correct, while class C throws a compiling error?

class A {
    int x = 1;
    A(int x) { this.x = x; }
}

class B extends A {
    B() { super(2); }
    B(int x) { super.x = x; } //Error
}

class C extends A {
    C() { super.x = 2; }      //Error
    C(int x) { super.x = x; } //Error
}

Answer 1

Because in the Constructor C() the Constructor A() is called - implicitly. You cannot prevent that, except by calling another constructor. But the constructor A() does not exist, just A(int) , thus error. (The default constructor only exists implicitly if you didn't write ANY other constructor - as soon as you have another constructor, you must add the default constructor or it won't exist).