Mastering Java: The Ultimate Quiz for 'Thinking in Java' 2025 - Free Java Programming Practice Questions and Study Guide

Calling a derived-class method that manipulates members not yet initialized can lead to undefined behavior because the members have not been initialized yet. This can result in unpredictable output and potentially cause unexpected results in the program. It is important to ensure that all members are properly initialized before accessing or manipulating them in methods. Options A and B, runtime error and compiler error, respectively, may also occur in this scenario depending on the specific implementation. Option D, correct output, is not likely as the members are not yet initialized.