Question

我想实现一个验证，它将接受来自textfield的数字（String），然后将其传递给double变量（如果是Int或double），否则抛出新的异常。

我已经实现了一个仅适用于Int数字的代码。你可以给我一个提示吗？

protected double validateDiameter() {
    try {
        if (stringDiameter != null) {
     //Checking stringDiameter if its a number by creating a for loop 
            //that check each character of the string. 
            //If the string contains only numbers 
            //the program will continue, if not an exception is thrown.

            int lengthofdiameter = stringDiameter.length();

            int DiameterCount = 0;

            for (int i = 0; i <= lengthofdiameter - 1; i++) {
                char t = stringDiameter.charAt(i);
                if (Character.isDigit(t)) {
                    DiameterCount++;
                }
            }

            if (lengthofdiameter == DiameterCount) {
                Diameter = Double.parseDouble(stringDiameter);
                if (Diameter <= 0 && Diameter >= 9) {
                    throw new Exception("");
                }

            } else {
                throw new Exception("");
            }
        }
    } catch (Exception e) {
        Diameter = 0.0;

        JOptionPane.showMessageDialog(null,
                "Wrong value on the input area.Please use number." + "\n" + "Check diameter input.",
                "Error message!",
                JOptionPane.ERROR_MESSAGE);
    }

    return Diameter;
}

谢谢

更新：

感谢大家的帮助。对此，我真的非常感激。对我有用的解决方案是：

protected double validateDiameter() {
    try {
        if (stringDiameter != null) {
            if (stringDiameter.matches("-?\\d+(\\.\\d+)?")) {
                Diameter = Double.parseDouble(stringDiameter);
            } else {
                throw new Exception("");
            }
            if (Diameter <= 0 || Diameter > 8) {
                throw new Exception("");
            }
        } else {
            throw new Exception("");
        }
    } catch (Exception e) {
        Diameter = 0.0;

        JOptionPane.showMessageDialog(null,
                "Wrong value on the input area.Please use number." + "\n" + 
                        "Check diameter input.",
                "Error message!",
                JOptionPane.ERROR_MESSAGE);
    }
    return Diameter;
}

Answer 1

我的是stringDiameter;基本上首先你尝试将输入解析为Integer;如果这不起作用你可以尝试加倍，如果这仍然不起作用，它意味着没有一个

    String s = "10.2";
    try {
        int i = Integer.parseInt(s);
        //int routine
        System.out.println(i);
    } catch (NumberFormatException e) {
        if (s.matches("-?\\d+(\\.\\d+)?")) {
            double d = Double.parseDouble(s);
            //double routine
            System.out.println(d);
        } else {
            // "Wrong value on the input area.Please use number." + "\n" + "Check                       //diameter input.", "Error message!",
            System.out.println("Wrong");
            throw new IllegalArgumentException();
        }
    }

Answer 2

boolean isDouble(String str) {
    try {
        Double.parseDouble(str);
        return true;
    } catch (NumberFormatException e) {
        return false;
    }
}

boolean isInteger(String s) {
    try { 
        Integer.parseInt(s); 
        return true;
    } catch(NumberFormatException e) { 
        return false; 
}

}

我必须承认我有点困惑你真正想要的东西。上面的代码检查给定的字符串是否为double，是您要查找的内容？

Answer 3

Ben和user1121883的答案均使用异常处理。如果在不使用异常的情况下需要解决方案（在检查时），那么我建议您在这里查看这些答案（以及以下答案）：

https://stackoverflow.com/a/5439547/1282908

https://stackoverflow.com/a/1102916/1282908

仅在Java中验证Int和双数

3 个答案: