字符串输入匹配条件后，while循环不断重复

Question

The code below is what I have written so far, so nothing has been implemented. However in the program it asks the user if the lowest grade is dropped. If the user replies by saying either "Yes","yes","No",or"no" the do loop should end and keep going through the rest of the code.

However even if i input those correct responses it keeps going through the loop. I'm pretty new a java, so apologies if this is really stupid.

Code:

import java.util.Scanner;
public class AvgGrade {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner input = new Scanner(System.in);
    int numTest=1;


    //Test Number Checker
    while(numTest<=1) {
        System.out.println("How many tests were given out");
        System.out.println("Must be more than 1");
        numTest=input.nextInt();
    }

    //Lowest Grade Dropped Checker
    boolean droppedLow=false;
    String dropAnswer="default";
    do{
        System.out.println("Is the lowest grade dropped?");
        System.out.println("Answer: Yes, yes, No, no");
        dropAnswer=input.next();
    }
    while(dropAnswer.compareTo("Yes")!=0||dropAnswer.compareTo("yes")!=0||
              dropAnswer.compareTo("No")!=0||dropAnswer.compareTo("no")!=0);

    if(dropAnswer.equals("Yes")||dropAnswer.equals("yes"))
        droppedLow=true;
    else if(dropAnswer.equals("No")||dropAnswer.equals("no"))
        droppedLow=false;




    System.out.println("----------------DEBUG----------------");
    System.out.println(numTest);
    System.out.println(dropAnswer);
    System.out.println(droppedLow);
}

}

Console/Output:

How many tests were given out
Must be more than 1
5
Is the lowest grade dropped?
Answer: Yes, yes, No, no
Yes
Is the lowest grade dropped?
Answer: Yes, yes, No, no
yes
Is the lowest grade dropped?
Answer: Yes, yes, No, no
no
Is the lowest grade dropped?
Answer: Yes, yes, No, no
No
Is the lowest grade dropped?
Answer: Yes, yes, No, no

Answer 1

This will always be true no matter what you type, so the loop will continue forever:

dropAnswer.compareTo("Yes")!=0||dropAnswer.compareTo("yes")!=0||
    dropAnswer.compareTo("No")!=0||dropAnswer.compareTo("no")!=0

Essentially, your condition means "loop if dropAnswer is unequal to 'Yes' OR it's unequal to 'yes' OR it's unequal to 'No' OR it's unequal to 'no.'" At least three of those conditions are always going to be true, since there's no string that's 'Yes', 'yes', 'No', and 'no' simultaneously.

I think you meant to use && (and) instead of || (or):

dropAnswer.compareTo("Yes") != 0 && dropAnswer.compareTo("yes") != 0 &&
    dropAnswer.compareTo("No") != 0 && dropAnswer.compareTo("no") != 0