Java — Identify which class-level (non-local) variable declarations will not compile

Introduction / Context:
This question tests knowledge of valid modifiers for class-level (non-local) variables in Java. Some modifiers are allowed for variables, while others are only valid for methods.

Given Data / Assumptions:

• Scope: class-level variables, not local or method-level.
• Keywords in play: protected, transient, synchronized, volatile.

Concept / Approach:
For variables:

• Access modifiers (public, protected, private) are valid.
• transient and volatile are valid modifiers for variables.
• synchronized is not valid for variables; it only applies to methods or blocks.

Step-by-Step Reasoning:

Why Other Options Are Wrong:
All except synchronized are legal modifiers for variables.

Common Pitfalls:
Confusing synchronized with volatile; synchronized is only for methods/blocks, not variables.

Final Answer:
private synchronized int e;