Java - Deleting previous console inputs out of System.in - Why does 1 version of my Code work and not the other version?

The diffrence in the code is in the deleteInput()-Method. Everything else is the same. The question is at the end, because it's about the console output.

The code:

public class DeletePreviousInputs {
    static Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) throws InterruptedException, IOException {
        System.out.println("write something in the console");
        /*
        * What I wrote:
        1 <enter> 2 <enter> 3 <enter> 4 <enter>
        */
        Thread.currentThread();
        Thread.sleep(8000); //simulates delay
        deleteInput();
        System.out.println("after input should be deleted");
        System.out.println(scanner.nextLine());
        System.out.println(scanner.nextLine());
        System.out.println(scanner.nextLine());
    }

    //Version 1 of the deleteInput()-Method:
    private static void deleteInput() throws InterruptedException {
        try {
            while (System.in.available() > 0) {
                //This is the part, where the code will differ in Version 2
                scanner.nextLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //Version 2 of the deleteInput()-Method:
    private static void deleteInput() throws InterruptedException {
        try {
            while (System.in.available() > 0) {
                //This is the part, where the code differs
                Scanner dummyScanner = new Scanner(System.in);
                dummyScanner.nextLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output version 1:

write something in the console
1
2
3
after input should be deleted
2
3

Output version 2:

write something in the console
1
2
3
after input should be deleted

Why does version 1 not delete/skip all of the previous input? Why does version 2 work perfectly?

I tried to delete all previous input of System.in so that only the latest/newest would be recognized by the Scanner. I didn't expect to see a diffrence in the functionality between the two deleteInput()-Methods. I do not understand why one version works and the other does not work.

Update:

@Sash (I can't answer to your comment for some reason, so I update here) I tried it and changed only the deleteInput()-method to this:

System.out.println("deleteInput()-method has started");
while (scanner.hasNextLine()) {
    scanner.nextLine();
}
System.out.println("deleteInput()-method has ended");

But that creates a loop and the method is never left. Here is the output I get:

write something in the console
1
2
3
deleteInput()-method has started

If I replace scanner.nextLine() with:

if(scanner.nextLine().isEmpty()) {
    break;
}

it also does not leave the method.

Version 1 of deleteInput

• scanner.nextLine() returns one line, but consumes the whole available input
• Therefore next System.out.println(scanner.nextLine()) has something to print,

Additional note: System.in.available() returns 0 after a single call to scanner.nextLine(), because whole input is consumed by scanner

---

Version 2 of deleteInput

• dummyScanner consumes the whole available input.
• Because of this, the original scanner.nextLine() has nothing to read
• Therefore, System.out.println(scanner.nextLine()) outputs nothing

---

Code to illustrate this behavior:

System.out.println("Input 3 lines");

Thread.currentThread();
Thread.sleep(8000);

System.out.println("After sleep");

Scanner scanner1 = new Scanner(System.in);
Scanner scanner2 = new Scanner(System.in);

System.out.println("scanner1.nextLine() - " + scanner1.nextLine());

if (System.in.available() > 0) {
    System.out.println("scanner2.nextLine() - " + scanner2.nextLine());
} else {
    System.out.println("No input available");
}

System.out.println("scanner1.nextLine() - " + scanner1.nextLine());
System.out.println("scanner1.nextLine() - " + scanner1.nextLine());

On input:

1
2
3

Output is:

After sleep
scanner1.nextLine() - 1
No input available
scanner1.nextLine() - 2
scanner1.nextLine() - 3