In a lot of universities, Java is educated as the first object-oriented programming (OOP) language due to its importance in industries and foundations to advanced ones. To support its self-study, we have developed Java Programming Learning Assistant System (JPLAS). JPLAS offers several types of exercise problems that have different learning goals and difficulty levels. Among them, Code Writing Problem (CWP) requests a student to write a source code that will pass a given test code on JUnit. In this study, we analyze 183 answer source codes from 61 students for the three problems in a 135min quiz at a Java programming course in Okayama University, Japan, in terms of the test code pass rate and the code similarity. The results show that the average pass rate is 73.9% and the average similarity is 45.28%. Unfortunately, many students could not complete correct codes and some students submitted identical codes.