Java — Which of the following are legal method declarations?

Introduction / Context:
This evaluates knowledge of valid method declarations and combinations of modifiers in Java.

Concept / Approach:
All provided combinations are syntactically legal:

• protected abstract → valid for abstract classes.
• static final → legal (cannot be overridden, final ensures this).
• synchronized public final → legal combination, just unusual.
• private native → legal; native methods are often private.

Step-by-Step:
All four compile correctly, though not all are meaningful in all contexts.

Final Answer:
All of them are legal declarations.