To answer this question, we need to understand the purpose and behavior of each method in the context of a servlet.
Option A) doPost() - This method is used to handle HTTP POST requests in a servlet. It is a standard method that can be overridden to provide custom functionality. Calling this method does not cause unpredictable results.
Option B) doGet() - This method is used to handle HTTP GET requests in a servlet. It is also a standard method that can be overridden. Calling this method does not cause unpredictable results.
Option C) System.out.println() - This method is used to print output to the console. It is not specific to servlets and does not cause unpredictable results in the context of a servlet.
Option D) System.exit(0) - This method is used to terminate the Java Virtual Machine (JVM) and exit the program. Calling this method within a servlet can cause unpredictable results because it abruptly terminates the execution of the servlet container, which may impact the ongoing processing of other requests and lead to unexpected behavior.
Therefore, the correct answer is D) System.exit(0). This option is correct because calling this method within a servlet can cause unpredictable results.