Solve this multiple-choice question and choose the correct option.

In Java, which of the following statements about extending classes and implementing interfaces is valid according to the language rules?

Difficulty: Easy

A class can extend any number of classes simultaneously.
A class can implement only one interface at a time.
A class can either extend a class or implement interfaces, but it cannot do both at the same time.
None of the above statements is valid in Java.
A class cannot extend another class if it already implements at least one interface.

Correct Answer: None of the above statements is valid in Java.

Explanation:

Introduction / Context:

Java uses single inheritance for classes and multiple inheritance for interfaces. Understanding these rules is essential when designing class hierarchies and answering interview questions about extends and implements. This question checks which informal statement matches the real language rules.

Given Data / Assumptions:

A Java class can have at most one direct superclass.
A Java class can implement one or more interfaces.
A class header can combine both extends and implements.

Concept / Approach:

The correct rule is that a class may extend exactly one other class (except for java.lang.Object, which has no superclass) and may implement zero or more interfaces. It is perfectly legal for a class to both extend a superclass and implement several interfaces in a single declaration, such as:

class MyService extends BaseService implements Runnable, AutoCloseable

Any statement that contradicts these facts is invalid.

Step-by-Step Solution:

Step 1: Evaluate option A, which claims that a class can extend many classes at once; this is false because Java does not support multiple class inheritance. Step 2: Evaluate option B, which restricts a class to only one interface; this is false because a class can implement several interfaces. Step 3: Evaluate option C, which claims that a class cannot extend and implement at the same time; this is false because the combined form is common. Step 4: Because A, B, and C are all false, option D, which states that none of the preceding statements is valid, becomes correct. Step 5: Confirm that option E is also false, since extending a class and implementing interfaces together is allowed.

Verification / Alternative check:

Compiling a class like class Demo extends Object implements Runnable, AutoCloseable shows that the compiler accepts this pattern, which disproves options B, C, and E. Trying to compile a class that extends two different superclasses results in a compilation error, which disproves option A.

Why Other Options Are Wrong:

Option A is wrong because Java restricts a class to one direct superclass. Option B is wrong because classes routinely implement multiple interfaces such as Serializable, Cloneable, and Comparable together. Option C is wrong because combining extends and implements in one header is fully supported. Option E is wrong because implementing an interface does not prevent a class from extending a superclass.

Common Pitfalls:

Many learners confuse Java with languages that allow full multiple inheritance for classes. Others mistakenly believe that implementing multiple interfaces is dangerous or not allowed. It is important to remember that Java chose single inheritance for classes to simplify the type system while still allowing flexible behavior composition through many interfaces.

Final Answer:

The correct choice is None of the above statements is valid in Java. because all the specific claims in the earlier options contradict the real inheritance and interface rules of the language.

Discussion & Comments

No comments yet. Be the first to comment!

In Java, which of the following statements about extending classes and implementing interfaces is valid according to the language rules?

More Questions from Technology

Discussion & Comments