In a Java interface, given that interface fields are implicitly public, static, and final, which of the following declarations of X are equivalent?

Introduction / Context:
This question focuses on how Java treats fields declared inside an interface. It tests your knowledge of default modifiers for interface variables and whether different looking declarations actually become the same at compile time. Understanding this is useful for reading and writing clean interface definitions.

Given Data / Assumptions:

• We have an interface with an int field X declared in three ways.
• The declarations are: 1) int X = 10, 2) public int X = 10, and 3) public static final int X = 10.
• The question assumes standard Java language rules for interface fields.
• We want to know which of these declarations are effectively the same.

Concept / Approach:
In Java, any variable declared inside an interface is implicitly public, static, and final. This means that even if you do not write these modifiers explicitly, the compiler treats the field as a constant that belongs to the interface type itself. As a result, int X = 10 inside an interface is automatically transformed into public static final int X = 10. Adding public explicitly does not change this behaviour, and writing all three modifiers only repeats what the language already assumes.

Step-by-Step Solution:
Step 1: Consider the simple interface declaration interface A { int X = 10; }.Step 2: The compiler treats this as if you wrote public static final int X = 10, even though you did not type those modifiers.Step 3: If you write public int X = 10, the compiler still adds static and final, resulting in the same compiled form.Step 4: If you write public static final int X = 10, you explicitly specify what was implicit in the previous two declarations.Step 5: Therefore declarations 1, 2, and 3 are all equivalent in an interface context, so the correct option is that all are equal.

Verification / Alternative check:
To verify, you can compile code that uses the different declarations and then use reflection or a decompiler to inspect the generated bytecode. You will see that in all three cases the field is marked as public, static, and final in the compiled class file. You can also try to assign to X from code that implements the interface and see that the assignment fails because X is final regardless of how it was declared in the interface source.

Why Other Options Are Wrong:
Option A and option B assume that only some pairs of declarations are equal, ignoring the fact that the compiler adds missing modifiers in every case. Option C claims all are unequal, which contradicts Java specification rules for interface fields. Only option D correctly reflects that all three declarations compile to the same public static final constant.

Common Pitfalls:
Developers sometimes forget that interface fields are constants and attempt to change their values at runtime, which results in compilation errors. Another pitfall is repeating modifiers unnecessarily and making the code verbose. Knowing that int X = 10 is sufficient and that it already implies public static final helps you write cleaner, more idiomatic interface definitions.

Final Answer:
All three declarations are equivalent inside a Java interface, so the correct choice is that all are equal.