用于创建对象的用户输入

Question

如果它与用户输入的值匹配，我正在尝试编写代码来创建特定对象。

例如：

假设我有 Person 类和 Car 类

public class Person
{
    private int x, y ,z;
    private String str;

    //Constructors etc
} 
public class Car
{
    private int x,y,z;
    private double doub;

    //Constructors etc
}

要求用户输入 4 个不同的值。 Person 和 Car 的前三个字段相同，但如果第 4 个值是 String 或 double，则程序应创建匹配对象。

public class Input
{
     public static void main (String args[])
     {
         int x,y,z;
         ?? other; //how do i declare if its either a double or string

         Scanner input = new SCanner(System.in);
         x = input.nextInt();
         // y, z input
         other = input.??? //String or double

         //Create matching object
     }
}

我该怎么办？

Answer 1

您可以使用matches 来检查您的输入是双精度还是字符串，例如：

Scanner input = new Scanner(System.in);
String other = input.nextLine();
if (other.matches("\\d+\\.\\d+")) {
    //your input is double
    Double d = Double.parseDouble(other);
    System.out.println("double = " + d);

} else {
    //your intput is a Strings
    System.out.println(other);
}

Answer 2

您可以使用object 输入类型并使用instanceof 进行检查

Scanner input = new SCanner(System.in);
x = input.nextInt();
// y, z input
string other = input.next();
Double d = null;
try {
  d = Double.parseDouble(other);
} catch (NumberFormatException e) {

}

Answer 3

您可以将 other 声明为全局字符串，然后检查它是否为双精度，您可以将其保存在双精度变量中。

     Scanner input = new SCanner(System.in);
     x = input.nextInt();
     // y, z input
     string other = input.next()

Answer 4

使用 instanceof 关键字试试这个。

        System.out.println("Enter value");
        String userIn = new Scanner(System.in).nextLine();

        try {
            if ((Double) Double.parseDouble(userIn) instanceof Double) {
                System.out.println("Double value is entered.");
                //Write your code here if it is double
            } else if (userIn instanceof String) {
                System.out.println("String is entered");
                //Write your code here if it is String
            }
        } catch (NumberFormatException ex) {
            System.out.println("String is entered");
            //Write your code here if it is String
        }

Answer 5

首先创建一个简单的String 来捕获用户输入，然后尝试将其解析为double。如果它可以解析它，则意味着输入了一个有效的 double 并且不会抛出异常，换句话说，它将执行 try 块中的代码。如果它无法解析（抛出异常），它将执行catch 块中的代码。

示例：

public static void main(String[] args) {

    Scanner kbd = new Scanner(System.in);
    System.out.println("Enter something...");
    String userInput = kbd.next();
    Car car = null; // create empty Car object to be able to use it outside of the try/catch block
    Person person = null; // create empty Person object to be able to use it outside of the try/catch block

    try {
        double d = Double.parseDouble(userInput);
        car = new Car();
    } catch (NumberFormatException e) {
        person = new Person();
    }

    // Ask user for new input and assign it to either Car or Person object as you develop your program...

}

Answer 6

另一种验证输入的方法是使用简单的try-catch，例如：

Scanner input = new Scanner(System.in);
String other = input.nextLine();
Car car = null;
Person person = null;

try {
    // Is your input double
    Double d = Double.parseDouble(other);
    System.out.println("double = " + d);

    car = new Car();
    // ******* Write your statements to handle Car here *******

} catch (NumberFormatExaception nfe) {
    //your intput is a String
    System.out.println(other);

    person = new Person();
    // ******* Write your statements to handle Person here *******

}