Question

Analyze the following code:

public class Test extends A {
public static void main(String[] args) {
Test t = new Test();
t.print();
}
}

class A {
String s;

A(String s) {
this.s = s;
}

public void print() {
System.out.println(s);
}
}

(Choose more than one)

A. The program does not compile because Test does not have a default constructor Test().
B. The program has an implicit default constructor Test(), but it cannot be compiled because its superclass does not have a default constructor. The program would compile if the constructor in class A were removed.
C. The program would compile if a default constructor A(){ } is added to class A explicitly.
D. The program compiles, but it has a runtime error due to the conflict on the method name print.

Answer 1

The code will not compile because class A does not have a default constructor, which is required when its subclass Test does not include an explicit call to a superclass constructor. Correcting this issue by adding a default constructor to class A or removing the existing constructor will allow the code to compile. There is no method name conflict that would cause a runtime error once the constructor issue is resolved.

Step-by-step explanation:

Analyzing the given code, we can see that class Test is extending class A. Class A contains a parameterized constructor but does not provide a default constructor. In Java, if a class has any constructors explicitly defined and it lacks a no-argument constructor, then Java does not provide a default constructor automatically. Class Test automatically inherits this situation from class A and requires an explicit default constructor or a matching constructor that calls super with the appropriate arguments to compile correctly.

Let's analyze the options given:

• A: This statement is incorrect because Java can indeed provide a default constructor, but the issue here is with class A not having a default constructor, which is required when creating an instance of class Test.
• B: This statement is correct. The program has a default constructor for Test, but it can't be compiled because class A lacks a default constructor. Furthermore, the claim is right about the program compiling if the constructor in class A is removed or a no-argument constructor is added.
• C: This statement is accurate. Adding a default constructor to class A explicitly would enable class Test to instantiate objects without runtime issues as it can then use the inherited default constructor.
• D: This option is incorrect. If the program were to compile (after fixing the constructor issue), it would not have a runtime error due to method name conflicts as method override is a common practice in object-oriented programming.

In conclusion, the correct answers are B and C: The program will compile if either class A's parameterized constructor is removed so that Java's default constructor can be implicitly used, or a default constructor for class A is explicitly added.

Answer 2

The program has an implicit default constructor Test(), but it cannot be compiled because its superclass does not have a default constructor. The program would compile if the constructor in class A were removed. The correct option is B.

Step-by-step explanation:

The code defines a class Test that extends another class A. The superclass A has a parameterized constructor, and since there is no default constructor, Java does not provide an implicit default constructor for class Test. In the main method of Test, an object of Test is created, but the absence of a default constructor in A results in a compilation error. Removing the constructor in class A would resolve this issue, allowing the program to compile successfully.

Option B is the answer.