Question

我不知道它是否在任何地方，但我只是想知道是否有任何解决方法，int无法解除引用错误。这就是我到目前为止所拥有的

int ch;
    JOptionPane.showMessageDialog (null, "1=+ 2=- 3=x 4=/ Please Choose Operation"); // Shows what numbers will do what operation when input
    ch = Integer.parseInt (JOptionPane.showInputDialog("Please Choose Operation")); // Prompts user to input a number 1-4 for the operation they want to do
    switch (ch) {
        case 1:
            JOptionPane.showMessageDialog(null,"You Chose Additon"); // Adds up all ten integers from above
            JOptionPane.showMessageDialog(null, one + two + three + four + five + six + seven + eight + nine + ten);
            break;
        case 2:
            JOptionPane.showMessageDialog(null,"You Chose Subtraction"); // Subtracts all 10 numbers, resulting answer can be negative
            JOptionPane.showMessageDialog(null, one - two - three - four - five - six - seven - eight - nine - ten);
            break;
        case 3:
            JOptionPane.showMessageDialog(null, "You Chose Multiplication Do not use zeroes");  // Multiplies all 10 integers, cannot use 0's since answer would be 0
            JOptionPane.showMessageDialog(null, one * two * three * four * five * six * seven * eight * nine * ten);
            break;
        case 4:
            JOptionPane.showMessageDialog(null,"You Chose Division Can't Divide by 0"); // Divdes all numbers, cannot use 0's because no dividing by 0
            JOptionPane.showMessageDialog(null, one / two / three / four / five / six / seven / eight / nine / ten);
            break;
        default:
            JOptionPane.showMessageDialog(null,"You have to choose an operation"); // If no operation is chosen, Program ceases and closes
            break;

我想知道是否有任何办法可以强制你输入操作。我试着做了

    boolean validInput2 = false;
        while (!validInput){
            if (ch.endswith(" "));

但是这看起来不起作用（我知道这不是整个代码，我只是一直陷入取消引用错误）是否有什么我可以做的来解决这个错误并仍然有代码工作？

Answer 1

它为我提供了一些小修复。

int ch;
        JOptionPane.showMessageDialog (null, "1=+ 2=- 3=x 4=/ Please Choose Operation"); // Shows what numbers will do what operation when input
        ch = (int)JOptionPane.showInputDialog("Please Choose Operation").charAt(0); // Prompts user to input a number 1-4 for the operation they want to do
        switch (ch) {
            case 1:
                JOptionPane.showMessageDialog(null,"You Chose Additon"); // Adds up all ten integers from above
                JOptionPane.showMessageDialog(null, one + two + three + four + five + six + seven + eight + nine + ten);
                break;
            case 45:
                JOptionPane.showMessageDialog(null,"You Chose Subtraction"); // Subtracts all 10 numbers, resulting answer can be negative
                JOptionPane.showMessageDialog(null, one - two - three - four - five - six - seven - eight - nine - ten);
                break;
            case 3:
                JOptionPane.showMessageDialog(null, "You Chose Multiplication Do not use zeroes");  // Multiplies all 10 integers, cannot use 0's since answer would be 0
                JOptionPane.showMessageDialog(null, one * two * three * four * five * six * seven * eight * nine * ten);
                break;
            case 4:
                JOptionPane.showMessageDialog(null,"You Chose Division Can't Divide by 0"); // Divdes all numbers, cannot use 0's because no dividing by 0
                JOptionPane.showMessageDialog(null, one / two / three / four / five / six / seven / eight / nine / ten);
                break;
            default:
                JOptionPane.showMessageDialog(null,"You have to choose an operation"); // If no operation is chosen, Program ceases and closes
                break;
    }

如果你想用int切换，你需要切换字符的ascii代码，就像我对' - '字符所做的那样。你也可以像这样切换字符本身：

 char ch = JOptionPane.showInputDialog("Please Choose Operation").charAt(0);

然后像这样切换

switch (ch) {
            case '+':

有了这个，你必须输入字符+ - * /才能使程序正常工作。我希望我能告诉你的是可以理解的，我希望你能找到它。

你可以强制用户输入这样的字符：

char ch = 0;
JOptionPane.showMessageDialog (null, "1=+ 2=- 3=x 4=/ Please Choose Operation");
        while(ch!='+'&&ch!='-'&&ch!='*'&&ch!='/'){
            ch = JOptionPane.showInputDialog("Please Choose Operation").charAt(0);
        }

- ＆gt; switch-statement追逐while-loop

Answer 2

另一种选择是创建从操作到消息的映射，然后从地图中立即生成结果。

    HashMap<Integer, String> map = new HashMap<>();
    map.put(43, "You chose Addition" + (1+2+4));
    map.put(45, "You chose Subtraction" + (1-2-4));
    map.put(47, "You chose Division" + (1/2));
    map.put(42, "You chose Multiplication" + (1*2*4));

    String operations  =Arrays.toString(map.keySet().stream().map(k -> (char)(int)k).toArray());
    int val = JOptionPane.showInputDialog(null,"enter operation: "+ operations).charAt(0);
    JOptionPane.showMessageDialog(null, map.get(val));

更新为了避免计算结果，我们可以使用Callable：

    HashMap<Integer, Callable<String>> map = new HashMap<>();
    map.put(43, () -> {
        System.out.println("hello");
        return "You choose Addition" + (1+2+3);
    });
    map.put(45, () -> "You chose Subtraction" + (1-2-4));
    map.put(47, ()->"You chose Division" + (1/2));
    map.put(42, () -> "You chose Multiplication" + (1*2*4));

    String operations  =Arrays.toString(map.keySet().stream().map(k -> (char)(int)k).toArray());
    int val = JOptionPane.showInputDialog(null,"enter operation: "+ operations).charAt(0);
    JOptionPane.showMessageDialog(null, map.get(val).call());

Int无法解除引用

2 个答案: