java - 为什么我没有收到正确的返回消息？

Question

这个问题已经有答案了:

How do I compare strings in Java? (23 个回答)

已关闭 10 年前。

下面有一段我无法工作的代码。我在主方法中获取输入，然后将该输入传递到另一个方法中以检查验证。但它并没有真正检查正确。如果我输入99对于 month和day我希望它能给我消息 Check Month 。

相反，我得到: THIS
THIS

如果我输入02月份和 99今天，我希望它给我消息:Check day 。相反，我得到 THIS THIS

如果我输入02对于这两者，我希望它能够运行并继续运行其他方法。相反，我得到 THIS THIS .

public class Date {

private Calendar parsedDate;

public static void main(String[] args) 
{
    Date main = new Date();
        System.out.println("Enter a date (use the format -> (MM/DD/YYYY)");

    //declare Scanner
    Scanner in = new Scanner (System.in);

    System.out.println("Enter a month (MM): ");
    String month = in.nextLine();

    System.out.println("Enter a day (DD): ");
    String day = in.nextLine();

    System.out.println("Enter a year (YYYY): ");
    String year = in.nextLine();

    if (main.isValidDate(month, day, year) == true) 
    {
        main.newFormat(month, day, year);
        main.isLeapYear(year);
        main.dayNumber(month, day);
    }
    else if (main.isValidDate(month, day, year) == false)
    {
        System.out.println("Invalid Input");
    }
}//end of main

private boolean isValidDate(String month, String day, String year) 
{
    //check month       
    if(month == "01" || month == "03" || month == "04" ||
       month == "05" || month == "06" || month == "07" || month == "08" ||
       month == "09" || month == "10" || month == "11" || month == "12")
    { 
        //check day
        if(day == "01" || day == "02" || day == "03" || day == "04" ||
           day == "05" || day == "06" || day == "07" || day == "08" ||
           day == "09" || day == "10" || day == "11" || day == "12" ||
           day == "13" || day == "14" || day == "15" || day == "16" ||
           day == "17" || day == "18" || day == "19" || day == "20" ||
           day == "21" || day == "22" || day == "23" || day == "24" ||
           day == "25" || day == "26" || day == "27" || day == "28" ||
           day == "29" || day == "30" || day == "31")
        {
            return true;
        }
        else
        {
            System.out.println("Check Day");
            return false;
        }
    }//end of check month
    else if (month == "02")
    {
        if (day == "28" || day == "29")
        {
            return true;
        }
    }//end of month 2
    else
    {
        System.out.println("THIS");
        return false;
    }

    parsedDate = null;// if it's valid set the parsed Calendar object up.
    return true;
}//end of isValidDate

Answer 1

您应该使用 equals 方法来比较字符串。使用 == 运算符时，您比较的是字符串的地址，而不是它们的内容。