Given: class Top { public Top(String s) { System.out.print("B"); } } public class Bottom2 extends Top { public Bottom2(String s) { System.out.print("D"); } public static void main(String [] args) { new Bottom2("C"); System.out.println(" "); } } What is the result?

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  1. BD

  2. DB

  3. BDC

  4. DBC

  5. Compilation fails

Show answer
Correct Option: E

AI Explanation

To answer this question, we need to understand the concept of inheritance and constructor chaining in Java.

In the given code, we have two classes: Top and Bottom2. The Bottom2 class extends the Top class, which means that Bottom2 inherits from Top. When a class extends another class, it inherits all the fields and methods of the parent class.

The Top class has a constructor that takes a String parameter and prints "B" when called. The Bottom2 class also has a constructor that takes a String parameter and prints "D" when called.

In the main method of the Bottom2 class, we create a new Bottom2 object and pass the string "C" as a parameter to the constructor. This will invoke the Bottom2 constructor. However, before the Bottom2 constructor is called, the parent Top constructor is called implicitly.

Here's the constructor chaining that occurs:

  1. The Bottom2 constructor is called.
  2. Since Bottom2 extends Top, the parent Top constructor is called first.
  3. The Top constructor prints "B".
  4. Then, the Bottom2 constructor prints "D".

Therefore, the output will be "BD". However, the correct answer is E - Compilation fails.

The reason for this is that the code does not provide an explicit call to the parent constructor in the Bottom2 constructor. Since the Top class does not have a default constructor (a constructor with no parameters), the Java compiler will not generate a default call to the parent constructor. Therefore, if you try to compile this code as is, it will result in a compilation error.

To fix this error, you can add an explicit call to the parent constructor using the super keyword in the Bottom2 constructor. Here's an example of how you can modify the code to compile successfully:

public Bottom2(String s) {
   super(s); // explicit call to the parent constructor
   System.out.print("D");
}

With this modification, the output will be "BD".

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