java while循环如何在循环中仅显示用户选择，而不是所有用户选项

Question

Hello I am working on this menu loop, but I am new to Java and eclipse and I have a few questions. My main issue is that when the user enters their selection, the program doesn't just output the user's selection, but also outputs all selections in the menu before the user's selection.

For example if the user enters g the program will read:

you have selected to quit 
you have selected the coin toss simulator 
you have selected the grade estimator

• Does anyone know how I can make it so it outputs only the user's selection?

Also, would you recommend I nest this loop under each selection and create a new loop that runs the user's selcetion, for example grade estimator when they select g ?

Any help would be appreciated, I've been stuck on this for a while!

{        
    Scanner anotherScanner = new Scanner(System.in);

    boolean usersSelection = false;

    String c = "againAgain";
    String upper = c.toUpperCase();
    while (!usersSelection)
    {
        System.out.println("" + "Selection: ");

        if (anotherScanner.hasNext("q"))
            c = anotherScanner.next();

        {
            usersSelection = true;

            System.out.println("you have selected to quit");
            ;
        }

        if (anotherScanner.hasNext("t"))
            c = anotherScanner.next();

        { 
            usersSelection = true;
            System.out.println("you have selected the coin toss estimator");
            ;
        }

        if (anotherScanner.hasNext("g"))
        {
            {
                c = anotherScanner.next();
                {
                    usersSelection = true;
                    System.out.println("you have selected the grade estimator");
                }
            }
        if (anotherScanner.hasNext("C"))
        {
             c = anotherScanner.next();

             {usersSelection = true;}

             System.out.print("You have selected color Challenge");
        }

        else
              break;

    }

    // { { System.out.print("Selection");}
}
}}}

Answer 1

Update if for q and t condition bracket like below :

if (anotherScanner.hasNext("q"))
        {     
          c = anotherScanner.next();
          usersSelection = true;
          System.out.println("you have selected to quit");
        }

The if condition not containing bracket due to which all the lines get executed

Answer 2

I'm not the greatest, but I'm bored so I'll give this a shot! First off I would suggest picking up some good books or doing a marathon of tutorials! There are a lot of good video tutorials out there :)

Your main problem here is scope.. ie) The problem is your braces. Please look at the following links!

http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html http://mindprod.com/jgloss/scope.html

Imagine a case where the scope is inside if(SomeBool)

1 - consider the following code:

{
...
    if(SomeBool)
    {
        int x = 5;
        x += 4;
        System.out.println(x)
    }
...
}

2 - It would have the same result as if I wrote

 {
    ...
        if(SomeBool)
        {
            int x = 5;
            {
                x += 4;
            }
            System.out.println(x)
        }
    ...
 }  

3 - However it would crash if I wrote

{
...
    if(SomeBool)
    int x = 5;
    x += 4;
...
}  

In case one, all the code is in the same scope and thus can access x .

In case two x += 4; is in a new level of scope, but x is contained in parent scope, so it is accessible by this new nested scope.

In case three x is declared within the different scope as the x += 4; statement. If you leave out brackets for an if(SomeBool) it will only act out the proceeding statement.

Case three is equivalent to:

{
...
    if(SomeBool)
    { // Enter scope
        int x = 5; // x created
    } // Leave scope x deleted

    x += 4;  // There is no x here
    System.out.println(x) // No x here either
...
}  

When we finish the code associated with our if(SomeBool) , x will be deleted because we are no longer in that scope and it is no longer referenced.

So try cleaning up your code with proper indents and braces. Then repost, because it is currently the equivalent of:

{        
    Scanner anotherScanner = new Scanner(System.in);
    boolean usersSelection = false;

    String c = "againAgain";
    String upper = c.toUpperCase();
    while (!usersSelection)
    {
        System.out.println("" + "Selection: ");

        if (anotherScanner.hasNext("q"))
        {
            c = anotherScanner.next();
        }

        usersSelection = true; 
        System.out.println("you have selected to quit");

        if (anotherScanner.hasNext("t"))
        {
            c = anotherScanner.next();
        }

        usersSelection = true;
        System.out.println("you have selected the coin toss estimator");

        if (anotherScanner.hasNext("g"))
        {
            c = anotherScanner.next();
            usersSelection = true;
            System.out.println("you have selected the grade estimator");
            if (anotherScanner.hasNext("C"))
            {
                c = anotherScanner.next();
                usersSelection = true;
                System.out.print("You have selected color Challenge");
            }
            else
            {
                break;
            }
        }

    }
}

Hope this sheds some light!