java - 用几个月切换语句

我的任务是打印格式化的String Month＃，是NNNN（其中＃号是字段monthNumber的值，而NNNN是字段monthName的值。问题是，当我单击getMonthName时，它显示为'空值'。

我该如何解决？

public class Month {
    // instance variables - replace the example below with your own
    private int monthNumber;
    private String monthName;
    private String newMonthName;

    /**
     * Constructor for objects of class Month
     */
    public Month(int input){
        if((input == 0) || (input > 12)){
            System.out.println("Error: Month number must be between 1 and 12");
        }
        else if(input < 0){
            System.out.println("Error: Month number must be positive");
        }
        else{ //the value of the input is valid
            System.out.println("Month number is VALID");
        }
        setMonthName(monthName);
        printMonth(input);
        monthNumber = input;
    }

    /**
     *
     */
    private void setMonthName(String monthName)
    {
        switch(monthNumber){
            case 1:
                monthName = "January";
                break;
            case 2:
                monthName = "February";
                break;
            case 3:
                monthName = "March";
                break;
            case 4:
                monthName = "April";
                break;
            case 5:
                monthName = "May";
                break;
            case 6:
                monthName = "June";
                break;
            case 7:
                monthName = "July";
                break;
            case 8:
                monthName = "August";
                break;
            case 9:
                monthName = "September";
                break;
            case 10:
                monthName = "October";
                break;
            case 11:
                monthName = "November";
                break;
            case 12:
                monthName = "December";
                break;
            default:
                monthName = "Invalid month";
                break;
        }
    }

    /**
     *
     */
    private void printMonth(int input)
    {
        switch(input){
            case 0:
                System.out.println("Month " + input + " is not a month");
                break;
            case 1:
                System.out.println("Month " + input + " is January");
                break;
            case 2:
                System.out.println("Month " + input + " is February");
                break;
            case 3:
                System.out.println("Month " + input + " is March");
                break;
            case 4:
                System.out.println("Month " + input + " is April");
                break;
            case 5:
                System.out.println("Month " + input + " is May");
                break;
            case 6:
                System.out.println("Month " + input + " is June");
                break;
            case 7:
                System.out.println("Month " + input + " is July");
                break;
            case 8:
                System.out.println("Month " + input + " is August");
                break;
            case 9:
                System.out.println("Month " + input + " is September");
                break;
            case 10:
                System.out.println("Month " + input + " is October");
                break;
            case 11:
                System.out.println("Month " + input + " is November");
                break;
            case 12:
                System.out.println("Month " + input + " is December");
                break;
            default:
                System.out.println("Month " + input + "is an invalid month");
                break;
        }
    }

    /**
     *
     */
    public int getMonthNumber()
    {
        return monthNumber;
    }

    /**
     *
     */
    public String getMonthName()
    {
        return monthName;
    }

}

最佳答案

抱歉，您似乎只在调用monthNumber之后才分配setMonthName()。

在您的构造函数中重新排列代码：

   monthNumber = input;
   setMonthName();
   printMonth(input);

同样，在setMonthName()中，您将分配给参数，由于具有相同的名称，该参数使该类中的字段蒙上了阴影。 （最好在IDE中打开该警告）。从setMonthName()中删除​​参数，然后您将在对象中实际设置该字段。

private void setMonthName()
{
    switch(monthNumber){
    [...]
    }
}

最后，与您提出的问题无关，我建议更改printMonth(int input)以使用对象中的字段，而不是从setMonthName()复制您的switch语句。

关于java - 用几个月切换语句，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/32876667/