Java variable not initialized in loops?

March 15, 2023

I’m doing a course management system using java, and I want to check if a course if already enrolled.

Here is my code

boolean duplicateCheck;

for (int i=0; i<enrolledCourses.size(); i++) {
    if (enrolledCourses.get(i) == searchResult.get(Integer.parseInt(userInput)-1)) {
        duplicateCheck = true;
        break;
    } else {
        duplicateCheck = false;
}

if (duplicateCheck) {
    System.out.println("You've already enrolled in this course!");
} else {
...
}

But in the second if statement it says

The local variable duplicateCheck may not have been initialized

What’s wrong with my code? What should I do to fix it?

>Solution :

Variables must be initialized before use！

Definite Assignment

Do you think that when statement if (duplicateCheck) is executed, duplicateCheck is already assigned?

But you overlooked one point, enrolledCourses.size() may be equal to zero, in this case, the for loop will not be entered, and duplicateCheck will not be assigned