Why does my ArrayList input loop add extra entries and display blank lines?

Courses
1

Hey everyone, I’m working on a Java project for my class and I’m stuck. I’m trying to create a program that asks the user how many courses they want to add, then lets them input the course IDs. But I’m running into a couple of issues:

  1. When I run the program, it shows ‘Enter Course:’ twice at the start. Why is this happening?
  2. When I print out the list, there’s a blank line at the beginning. What’s causing this?

Here’s a snippet of my code:

ArrayList<String> courseList = new ArrayList<>();
Scanner input = new Scanner(System.in);
System.out.println("How many courses do you want to add?");
int count = input.nextInt();
System.out.println("Enter the course IDs:");
while(count > 0) {
    System.out.println("Course ID:");
    String course = input.nextLine();
    courseList.add(course);
    count--;
}

for (String course : courseList) {
    System.out.println(course);
}

Can anyone spot what I’m doing wrong? I’m really confused and could use some help. Thanks!

2

I’ve encountered this issue before in my Java projects. The problem stems from how Scanner handles input streams. After nextInt(), the newline character remains in the buffer, causing nextLine() to read an empty string.

To fix this, add an extra input.nextLine() after nextInt() to consume the leftover newline:

int count = input.nextInt();
input.nextLine(); // Consume newline

This should resolve both the double prompt and blank line issues. Also, consider using a do-while loop instead of a while loop for a more natural flow:

do {
    System.out.println('Course ID:');
    String course = input.nextLine();
    courseList.add(course);
    count--;
} while (count > 0);

This approach ensures the prompt appears the correct number of times and eliminates the need for an initial prompt outside the loop.

3

hey surfingwave, i ran into this too. scanner’s nextInt() doesn’t consume the newline so your nextLine() grabs an empty one. try calling input.nextLine() right after nextInt() and it should fix the dup prompt and blank line. lmk if it works!

4

Hey SurfingWave! :ocean:

I totally get your frustration - I’ve been there too! Let me take a stab at explaining what might be going on.

So, about that double ‘Enter Course:’ prompt… It’s probably because of how Scanner handles the newline character after you enter the number of courses. When you use nextInt(), it doesn’t consume the newline, so the first nextLine() call is actually reading that empty line. Sneaky, right?

And that blank line at the beginning of your output? It’s likely coming from that same issue - you’re adding an empty string as the first course.

Have you tried adding a input.nextLine() right after the nextInt() to clear out that pesky newline? Something like this:

int count = input.nextInt();
input.nextLine(); // Add this line to consume the newline

Give that a shot and see if it helps! If you’re still stuck, let me know and we can brainstorm some more. What other cool features are you adding to your course management system?