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

In Java, consider the invalid class header written as \"X implements Y extends Z\". What actually happens if you attempt to compile a class declaration that uses implements before extends in this way?

Difficulty: Medium

X can be a class and Y and Z must both be interfaces, so the code compiles successfully.
X must be an interface and Y and Z must be classes, so the code compiles successfully.
X and Y must be classes and Z must be an interface, so the code compiles successfully.
The compiler reports an error because in Java a class must extend a superclass before it implements interfaces in the header.
The code compiles successfully, but the interfaces specified after implements are ignored by the JVM.

Correct Answer: The compiler reports an error because in Java a class must extend a superclass before it implements interfaces in the header.

Explanation:

Introduction / Context:

Java has a strict syntax for class declarations that combine inheritance and interface implementation. Interview questions often test whether candidates know the correct ordering of extends and implements in a class header and what happens when that order is violated, as in the expression \"X implements Y extends Z\".

Given Data / Assumptions:

An ordinary Java class can extend at most one direct superclass.
That same class can implement one or more interfaces.
The language grammar defines a fixed order for these clauses.

Concept / Approach:

The valid form of a Java class header that uses both inheritance and interfaces is:

class X extends Z implements Y1, Y2, ...

First the class may extend a single superclass using the extends keyword. After that, the class may implement one or more interfaces using the implements keyword. Reversing the order to \"implements ... extends ...\" does not match the Java grammar, so the compiler cannot parse it as a valid declaration and must report a compilation error.

Step-by-Step Solution:

Step 1: Rewrite the expression in a realistic form, such as class X implements Y extends Z. Step 2: Compare it with the correct pattern class X extends Z implements Y. Step 3: Notice that implements appears before extends, which violates the Java grammar. Step 4: Recognize that the compiler will fail to parse this header correctly. Step 5: Conclude that the result is a compilation error rather than a valid type declaration.

Verification / Alternative check:

If a developer copies such a header into a Java source file and attempts to compile it with javac, the compiler issues an error message indicating a syntax problem near the implements or extends keyword. Changing the order to \"extends Z implements Y\" immediately resolves the error, confirming that ordering is mandatory.

Why Other Options Are Wrong:

Option A is wrong because even if X, Y, and Z have valid roles, the syntax order is still invalid. Option B is wrong because X cannot be both an interface and use that class style header. Option C is wrong because Java does not interpret the sequence in a way that makes this combination valid. Option E is wrong because the code does not compile at all, so there is nothing for the JVM to ignore or execute.

Common Pitfalls:

A common mistake is to assume that the compiler may reorder extends and implements automatically, which it does not. Another pitfall is confusing the syntax rules for classes with those for interfaces, where multiple inheritance of interfaces is allowed but still uses a consistent grammar.

Final Answer:

The correct choice is The compiler reports an error because in Java a class must extend a superclass before it implements interfaces in the header. because it reflects the strict ordering rules of the Java class declaration syntax.

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In Java, consider the invalid class header written as \"X implements Y extends Z\". What actually happens if you attempt to compile a class declaration that uses implements before extends in this way?

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