当不应该循环时，while循环不断重复

Question

I am getting a user input and using a while loop to keep validating the input. However, no matter what type of input I enter that is supposed to be true, it keeps returning false and repeating the loop.

This is the section of the code that uses the loop:

String deletelName;

System.out.println("Type patient's last name to delete");
deletelName = cin.next();   

Patient removePatient = new Patient (deletelName.toLowerCase(),null,null,null,null);

while (!bst.contains(removePatient)) {
    System.out.println("Patient's last name does not exist. Type another last name : ");
    deletelName = cin.next();
}   

Part of the bst class:

public boolean contains(AnyType x)
{
    return contains(x, root);
}


private boolean contains(AnyType x, BinaryNode<AnyType> t)
{
    if (t == null)
        return false;

    int compareResult = x.compareTo(t.element);

    if(compareResult < 0)
        return contains(x, t.left);

    else if (compareResult > 0)
        return contains (x, t.right);
    else
        return true;
}

Answer 1

removePatient isn't changing, only deletelName. So in order to fix your problem, add in removePatient = new Patient (deletelName.toLowerCase(),null,null,null,null); at the end of your loop.

Answer 2

This will go on forever for a very obvious reason: you are not making a new patient each time because this line

Patient removePatient = new Patient (deletelName.toLowerCase(),null,null,null,null);

is not in the while loop, and therefore it always checks with the same Patient . The solution is to replace this:

Patient removePatient = new Patient (deletelName.toLowerCase(),null,null,null,null);

while (!bst.contains(removePatient)) {
    System.out.println("Patient's last name does not exist. Type another last name : ");
    deletelName = cin.next();
}

With something like this:

Patient removePatient = new Patient (deletelName.toLowerCase(),null,null,null,null);

while (!bst.contains(removePatient)) {
    System.out.println("Patient's last name does not exist. Type another last name : ");
    deletelName = cin.next();
    removePatient = new Patient (deletelName.toLowerCase(),null,null,null,null);

}