Question

如何访问变量＆＃39; user_input＆＃39; ＆安培;实例＆＃39; c1＆＃39;？根据我的理解，它们在if-else语句@ choice 1的范围之外是不可访问的。

请参阅以下内容：

 public static void main (String [] args)
{
    int choice;
    int user_input;

    Scanner in = new Scanner (System.in);

    do
    {
        System.out.println ("==== Circle Computation =========");
        System.out.println ("| 1. Create a new circle\t|");
        System.out.println ("| 2. Print area\t\t\t|");
        System.out.println ("| 3. Print circumference\t|");
        System.out.println ("| 4. Quit\t\t\t|");

        System.out.println ("Choose option (1 - 3): ");
        choice = in.nextInt();

        if (choice == 1)
        {
            System.out.println ("Enter the radius to compute the area & circumference:");
            user_input = in.nextInt();              

            Circle c1 = new Circle(user_input);     //refer to prob @ choice '2'
            System.out.println ("A new circle is created.\n");
        }

        if (choice == 2)
        {           
            //Prob - instance 'c1' & var 'user_input' @ choice '1' not visible in other if-else statements?
            //http://stackoverflow.com/questions/11685023/creating-an-instance-of-an-object-within-an-if-in-c-sharp
            System.out.println ("Area of circle:");
            System.out.println ("Radius: " + c1.getRadius());
            System.out.println ("Area: " + c1.area());
        }

Answer 1

Circle c1在if语句中定义，因此只能在那里访问。

user_input在while循环之外定义，因此可以在整个循环中访问

每个变量都有definition scope。当块中定义的变量c（在{和}之间）时，它仅限于该范围，这意味着它只能在该范围内引用。

Answer 2

变量user_input在if条件下均可访问，因为其范围为main方法

声明

if (choice == 1)
{
    System.out.println ("Enter the radius to compute the area & circumference:");
    user_input = in.nextInt();              

    Circle c1 = new Circle(user_input);     //refer to prob @ choice '2'
    System.out.println ("A new circle is created.\n");
}

c1的范围是括号，如果条件。如果您希望在其他if循环中访问它，那么您可能希望将c1移出如下所示。我已将c1的范围更改为main方法，以便它符合您的逻辑。

    Circle c1 = null;
    do
    {
        System.out.println ("==== Circle Computation =========");
        System.out.println ("| 1. Create a new circle\t|");
        System.out.println ("| 2. Print area\t\t\t|");
        System.out.println ("| 3. Print circumference\t|");
        System.out.println ("| 4. Quit\t\t\t|");

        System.out.println ("Choose option (1 - 3): ");
        choice = in.nextInt();
        if (choice == 1)
        {
            System.out.println ("Enter the radius to compute the area & circumference:");
            user_input = in.nextInt();              

            c1 = new Circle(user_input);     //refer to prob @ choice '2'
            System.out.println ("A new circle is created.\n");
        }

        if (choice == 2)
        {           
            //Prob - instance 'c1' & var 'user_input' @ choice '1' not visible in other if-else statements?
            //http://stackoverflow.com/questions/11685023/creating-an-instance-of-an-object-within-an-if-in-c-sharp
            System.out.println ("Area of circle:");
            System.out.println ("Radius: " + c1.getRadius());
            System.out.println ("Area: " + c1.area());
        }           
    }

Answer 3

user_input 变量创建到主方法块
中所以它可以访问if或else阻止。但 C1 无法访问，因为它是IF块的本地变量/实例

Answer 4

User_input可以在整个方法中使用。

C1不能用于第二部分

如何访问实例＆amp; if else语句中的变量

4 个答案: