如何逃避while循环

Question

I wrote the following method, which boolean-return type is again assigned to another boolean in another method in which I call this method.

    private boolean answer() {

    Scanner input = new Scanner(System.in);
    boolean b = false;
    String answer = input.nextLine();

    while(answer != "y" || answer != "n") {
        System.out.println("Answer with y (yes) or n (no)");
        answer = input.nextLine();
    }
    if (answer == "y") {
        b = true;
    }
    return b;

}

But no matter what I type in (y, n, or any other letter), I always end up in the while-loop again.

Answer 1

It's because you have an or rather than and on your test.

As it's currently coded you are saying:

while the answer isn't "y" or it isn't "n", loop.

which will always be the case.

What you want is:

while the answer isn't "y" and it isn't "n", loop.

which is coded as:

while (answer != "y" && answer != "n") (

Answer 2

更改为： while(answer != "y" && answer != "n") ，您的代码将按预期工作。

Answer 3

I suspect your problem lies here: while(answer != "y" || answer != "n")

When your answer = "y" it isn't = "n" so the loop continues and vice verse.

Probably you want this: while(answer != "y" && answer != "n")

Answer 4

I changed your code a bit to accept a char instead.

Here is the code:

private boolean answer() {

    Scanner input = new Scanner(System.in);
    boolean b = false;

    char answer = input.nextLine().toLowerCase().charAt(0);

    while(answer != 'y' || answer != 'n' ) {
        System.out.println("Answer with y (yes) or n (no)");
        //lower case so that it will get y or n, no matter what the casing is
        answer = input.nextLine().toLowerCase().charAt(0);
    }
    if (answer == 'y') {
        b = true;
    }
    return b;

}

or if you really want a string

private boolean answer() {

    Scanner input = new Scanner(System.in);
    boolean b = false;
    String answer = input.nextLine();

    while( !(answer.equalsIgnoreCase("y") || answer.equalsIgnoreCase("n")) ) {
        System.out.println("Answer with y (yes) or n (no)");
        answer = input.nextLine();
    }
    if (answer.equalsIgnoreCase("y")) {
        b = true;
    }
    return b;
}

Remember to use .equals() or .equalsIgnoreCase() when comparing two Strings