Analyze the following code: _____public class A extends B {}class B { public B(String s) { }}A. The program has a compile error because A does not have a default constructor.B. The program has a compile error because the default constructor of A invokes the default constructor of B, but B does not have a default constructor.C. The program would compile fine if you add the following constructor into A: A(String s) { }D. The program would compile fine if you add the following constructor into A: A(String s) { super(s); }
Question
Analyze the following code: _____public class A extends B {}class B { public B(String s) { }}A. The program has a compile error because A does not have a default constructor.B. The program has a compile error because the default constructor of A invokes the default constructor of B, but B does not have a default constructor.C. The program would compile fine if you add the following constructor into A: A(String s) { }D. The program would compile fine if you add the following constructor into A: A(String s) { super(s); }
Solution
The correct answer is B. The program has a compile error because the default constructor of A invokes the default constructor of B, but B does not have a default constructor.
Here's why:
In Java, when you create a subclass (A) of a superclass (B), the subclass inherits the properties and methods of the superclass. When you create an object of the subclass, it automatically calls the default constructor of the superclass (B) before it calls the constructor of the subclass (A).
In this case, class B does not have a default constructor because a parameterized constructor is defined. Java does not provide a default constructor if you have defined any constructor in your class.
So, when you create an object of class A, it tries to call the default constructor of class B, but it doesn't exist, hence the compile error.
Option C and D are incorrect because adding a constructor in class A does not solve the problem. The problem is with class B not having a default constructor, not class A.
So, to fix the error, you need to add a default constructor in class B or modify class A to call the existing constructor of class B using the super keyword.
Similar Questions
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