JOptionPane 切换语句循环

Question

@MadProgrammer，switch-case 函数在一次选择后停止。我似乎无法让它回到 OnlineStore( )。我试过 do-while 语句。它没有用。无论输入 1 还是 2，它都会进入默认状态然后返回菜单。

        import javax.swing.JOptionPane;

        public class OnlineStore 
        {
            String[] ColorType = {"blue", "green", "black"}; 
            final int COLOURS = 3;    // t choices
            int[] Color = new int[COLOURS];
            int sum, mselect;

            public static int display_menu() // Not the main program but the main menu.
            {
                String input;
                int mselect;
                input = JOptionPane.showInputDialog("Welcome!" + "\n\n1. Add tshirt order\n2. Edit tshirt order\n3. View current order\n4. Checkout" + "\n\nPlease enter your choice: ");
                // return Integer.parseInt(input);
                mselect = Integer.parseInt(input);
                return 0;
            }

            public OnlineStore() // Switch-case program
            {
                do 
                {
                display_menu();
                switch (mselect)
                { 
                     case 1:
                        add_t();
                        break;
                    case 2:
                        edit_t();
                        break;
                    default:  // If an error is encountered.
                        JOptionPane.showMessageDialog(null, "Oh dear! Error!");
                        break;
                }
                } while (mselect < 3);
            }

            public final int add_t()
            {  
                for (int index = 0; index < ColorType.length; index++)
                {
        <output>
                }
                return Color.length;
            }

            public final int edit_t() 
            {
                for (int index = 0; index < ColorType.length; index++)
                {
        <output>
            }

            public static void main(String[] args) // Main program
            {
                new OnlineStore(); // Call out the program.
            }

        }

Answer 1

您似乎没有为 mselect 赋值。您可能想要做的是

        int sum;
        static int mselect = 0;

        public static int display_menu() // Not the main program but the main menu.
        {
            String input;
            input = JOptionPane.showInputDialog("Welcome!" + "\n\n1. Add tshirt order\n2. Edit tshirt order\n3. View current order\n4. Checkout" + "\n\nPlease enter your choice: ");
            // return Integer.parseInt(input);
            mselect = Integer.parseInt(input);
            return 0;
        }

Answer 2

您正在将输入分配给局部变量。它的范围只与方法有关。 local Variable scope

mselect = Integer.parseInt(input);
return mselect;

并分配

mselect = display_menu();

或将 mselect 设为静态并删除局部变量。

Answer 3

首先...

public static int display_menu() // Not the main program but the main menu.
{
    String input;
    int mselect;
    input = JOptionPane.showInputDialog("Welcome!" + "\n\n1. Add tshirt order\n2. Edit tshirt order\n3. View current order\n4. Checkout" + "\n\nPlease enter your choice: ");
    // return Integer.parseInt(input);
    mselect = Integer.parseInt(input);
    return 0;
}

您没有返回 mselect，而是返回 0。相反，您可能应该做一些更像...

public static int display_menu() // Not the main program but the main menu.
{
    String input;
    input = JOptionPane.showInputDialog("Welcome!" + "\n\n1. Add tshirt order\n2. Edit tshirt order\n3. View current order\n4. Checkout" + "\n\nPlease enter your choice: ");
    // return Integer.parseInt(input);
    return Integer.parseInt(input);
}

接下来，您正在使用 mselect，它没有任何价值可以签入您的 switch

public OnlineStore() // Switch-case program
{
    do {
        display_menu();
        switch (mselect) {
            case 1:
                add_t();
                break;
            case 2:
                edit_t();
                break;
            default:  // If an error is encountered.
                JOptionPane.showMessageDialog(null, "Oh dear! Error!");
                break;
        }
    } while (mselect < 3);
}

但是，您应该使用 display_menu()

的返回值

public OnlineStore() // Switch-case program
{
    do {
        switch (display_menu()) {
            case 1:
                add_t();
                break;
            case 2:
                edit_t();
                break;
            default:  // If an error is encountered.
                JOptionPane.showMessageDialog(null, "Oh dear! Error!");
                break;
        }
    } while (mselect < 3);
}

非常警惕 static，它不是你的朋友，很容易将一个不错的运行程序变成垃圾。

相反，您可以做更像...

public class OnlineStore {

    String[] ColorType = {"blue", "green", "black"};
    final int COLOURS = 3;    // t choices
    int[] Color = new int[COLOURS];
    int sum;

    public int display_menu() // Not the main program but the main menu.
    {
        String input;
        input = JOptionPane.showInputDialog("Welcome!" + "\n\n1. Add tshirt order\n2. Edit tshirt order\n3. View current order\n4. Checkout" + "\n\nPlease enter your choice: ");
        // return Integer.parseInt(input);
        return Integer.parseInt(input);
    }

    public OnlineStore() // Switch-case program
    {
        boolean exit = false;
        do {
            switch (display_menu()) {
                case 1:
                    add_t();
                    break;
                case 2:
                    edit_t();
                    break;
                case 4:
                    exit = true;
                    break;
                default:  // If an error is encountered.
                    JOptionPane.showMessageDialog(null, "Oh dear! Error!");
                    break;
            }
        } while (!exit);
    }

    public final int add_t() {
        return 0;
    }

    public final int edit_t() {
        return 0;
    }

    public static void main(String[] args) // Main program
    {
        new OnlineStore(); // Call out the program.
    }

}

JOptionPane 切换语句循环

JOptionPane switch statement loop

java

swing

joptionpane

switch-statement