To assist Java programming educations, we have developed a Web-based Java Programming Learning Assistant System (JPLAS). JPLAS provides the element fill-in-blank problem to help novice students self-study Java programming by filling in blanked elements in a code. However, it is a pity that this problem can be solvable without reading the algorithm in the code, especially if students are familiar with grammar. In this paper, we propose the value trace problem to answer the changing values of important variables in a Java code that implements a fundamental data structure or algorithm , so as to improve the code reading capability. To verify the effectiveness, we generated five problems using Java codes for sorting and asked 10 students in our group to solve them.