What signs indicate that Java code cannot be successfully compiled?

Signs that Java code cannot be successfully compiled include:

• Syntax errors, such as missing semicolons, incorrect use of keywords.
• Type mismatches, such as attempting to assign a value of one type to a variable of another type without explicit conversion.
• Missing declared classes, methods, or variables that are referenced.
• Access rule violations (e.g., trying to access a private member from another class).
• Method signature mismatches during overriding.

The Java compiler will produce error messages indicating the line and reason, which helps quickly identify and fix the problem.