java将数字输入转换为一年

Question

我的目标是通过输入一个整数来询问用户年份。例如，如果用户输入“05”或“87”或“2017”，则输出将为“2005”或“2087”或仅为“2017”。该程序只意味着在输入中占2和4个空格。例如，如果用户输入“123”，则输出为“123是无效年份”或“12345”，输出为“12345不是年份”。我在代码中遇到问题，不知道如何更正它

import java.util.Scanner;

public class Y2k
{
  public static void main( String [ ] args )
  {
    Scanner scan = new Scanner ( System.in );

    // establish string and number to be apply to input
    String year;
    int sand = 20;

    // ask for the year 
    System.out.println( "Enter a year: " );
    year = scan.next( );
    char ohTwo = year.charAt( 1 );

    // perform the year and print the result
    switch ( year )
    {
      case "05": 
        System.out.println( sand + year ); //output year and input
        break;
    }
  }
}

对于这件事上的任何帮助，提前谢谢你

Answer 1

要使用switch语句实际实现这一点，请执行以下操作：

import java.util.Scanner;

public class Y2k
{
  public static void main(String [] args)
  {
    Scanner scan = new Scanner (System.in);

    // establish string and number to be apply to input
    String year;
    int sand = 20;

    // ask for the year 
    System.out.println("Enter a year: ");
    year = scan.next();

    try {
      System.out.println(getYear(year)); //output year and input
    } catch (Exception e) {
      System.out.println(e.getMessage());
    }
  }

  public String getYear(String input) {
    String sand = "20"
    // Typically also check that input is in fact an integer, in a sane range, etc.
    switch (input.length()) {
      case 2: 
        return sand + input;
      case 4: 
        return input;
      default:
        throw new RuntimeException(input + " is an invalid year.");
    }
  }
}

Answer 2

如果要使用switch，请执行以下操作，而不是if-else语句：

    switch(year.length()){
            case 2:
                System.out.println(sand + year);
            break;
            case 4:
                System.out.println(year);
            break;
            default:
                System.out.println(year+" is an invalid year.");
            break;
        }

Answer 3

这是使用“if”语句实现的程序：

import java.util.Scanner;

public class Y2k{

    public static void main(String[]args){

        Scanner scan = new Scanner(System.in);

        // establish string and number to be apply to input
        String year;

        int sand = 20;


         // ask for the year 
         System.out.println( "Enter a year: ");
         year = scan.next();

        if(year.length() == 2){
            System.out.println(sand + year);
        } 
        else if(year.length() == 4){
            System.out.println(year);
        }
        else{
            System.out.println(year+" is an invalid year.");
        }

    }
}

此解决方案使用“if”语句。您可以将此作为使用case方法创建自己的代码的指南