A Web-based Java Programming Learning Assistant System (JPLAS) has been developed to help novice students studying Java programming through self-learning. As one function, JPLAS provides the fill-in-blank problem that requests filling in the blank elements in a given code with several blanks. Currently, reserved words, identifiers, or control symbols can be blanked to have unique correct answers, which may be solved without reading the code carefully. In this paper, we propose to additionally blank operators in conditional expressions of core statements in the code so that students can understand the structure to realize the specification. For preliminary evaluations, we generated six operator fill-in-blank problems, and assigned them to students where the number of answer submissions per blank has increased from that of conventional problems.