Can you give a specific example of an error occurring during development or execution of a program?

One common case of error in Java is NullPointerException. For example, when trying to call a method on an object that has not been initialized (i.e., is null):

String text = null;
int length = text.length(); // this will throw NullPointerException

This error occurs at runtime and indicates that we are trying to access a method or field on a non-existent object. To avoid this, you should check objects for null before using them or use modern constructs like Optional.