Question

As part of my homework, I need to make a program that requires user input. For now I’m sticking with the console, however I’d like to avoid a crash due to newline characters.

This is a test, it acts similarly to what I’m trying to do and crashes due to even one newline character

public void testRead() {

    Scanner input = new Scanner(System.in);

    String s1 = "", s2 = "", s3 = "", s4 = "", s5 = "";

    while (s1 == "" || s1 =="\n") 
        if (input.hasNext()) {
            s1 = input.nextLine();
        }
    while (s2 == "" || s2 =="\n") 
        if (input.hasNext()) {
            s2 = input.nextLine();
        }
    while (s3 == "" || s3 == "\n") 
        if (input.hasNext()) {
            s3 = input.nextLine();
        }
    while (s4 == "" || s4 == "\n") 
        if (input.hasNext()) {
            s4 = input.nextLine();
        }
    while (s5 == "" || s5 == "\n") 
        if (input.hasNext()) {
            s5 = input.nextLine();
        }
        // Here is why it might crash
    if (input.hasNextInt()) // even though it should not pass this if
            // However the if is not the issue. 
            // This input may even be in another function
           int crash = input.nextLine();

    System.out.println("s1: " + s1);
    System.out.println("s2: " + s2);
    System.out.println("s3: " + s3);
    System.out.println("s4: " + s4);
    System.out.println("s5: " + s5);
}

}

I hoped the while statement would solve it, but it does not.

I could solve the crash, but that would not fix the problem since I would still have empty strings and what not.

Example

This is the first string
This is the second string
                                          <- pressed enter again, by mistake or not
This is the third string
This is the fourth string

Output

s1: This is the first string
s2: This is the second string
s3:
s4: This is the third string
s5: This is the fourth string

// now crash. Again, the crash can be avoided, but I still have a problem where string 3 has not been read or contains …. something I don’t want.

Is there an easy way of solving this issue ? if there is no easy way, I would rather ignore it and finish my homework fast, but I would still like to know the long answer for future reference.

Answer 1

you cannot use == for string contents equality, try this for ex:

 while (s1.equals("") || s1.equals("\n")) 
        if (input.hasNext()) {
            s1 = input.nextLine();
        }
    while (s2.equals("") || s2.equals("\n")) 
        if (input.hasNext()) {
            s2 = input.nextLine();
        }
    while (s3.equals("") || s3.equals("\n")) 
        if (input.hasNext()) {
            s3 = input.nextLine();
        }
    while (s4.equals("") || s4.equals("\n")) 
        if (input.hasNext()) {
            s4 = input.nextLine();
        }
    while (s5.equals("") || s5.equals("\n")) 
        if (input.hasNext()) {
            s5 = input.nextLine();
        }