在java中将美国日期转换为EU日期

Question

Without using a "dateformat" or something along those lines, I am trying to change a string of US date "mm/dd/yyyy" to an EU format "dd/mm/yyyy". I am to do this using strings and string methods. I feel like I am very close to this but cannot quite figure it out. This is my code:

import java.util.Scanner;

public class DateChange {

    public static void main(String[] args) {
        Scanner kbd = new Scanner(System.in);
        String usDate, euDate, day, month;
        int year;
        System.out.println("Enter a date in the form month/day/year:");
        usDate = kbd.nextLine();
        month = usDate.substring(0, '/');
        day = usDate.substring('/', '/');
        year = usDate.lastIndexOf('/');
        euDate = day + "." + month + "." + year;
        System.out.println("Your date in European form is:");
        System.out.println(euDate);
    }

}

This is the error I am getting:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 47
    at java.lang.String.substring(String.java:1963)
    at DateChange.main(DateChange.java:12)

Answer 1

Why not split the input string using '/' as separator using the method String.split . It returns an array of strings. Just swap the first two elements of the array.

String usdate = "12/27/2015";
String[] arr = usdate.split("/");
String eudate = arr[1] + "/" + arr[0] + "/" + arr[2];

Answer 2

The problem is that java.String.substring takes two int values, not char values. The int value of ' / ' is 47, so substring is taking 47 as an input, not the indexOf ' / '.

If you want to solve this without using the java library, use the following code:

import java.util.*;

public class DateChange {
    public static void main(String[] args) {
        Scanner kbd = new Scanner(System.in);
        String usDate, euDate, day = "", month = "", year = "";
        System.out.println("Enter a date in the form month/day/year:");
        usDate = kbd.nextLine();
        kbd.close();
        month = usDate.substring(0, usDate.indexOf("/"));
        day = usDate.substring(usDate.indexOf("/")+1, usDate.lastIndexOf("/"));
        year = usDate.substring(usDate.lastIndexOf("/")+1, usDate.length());
        euDate = day + "." + month + "." + year;
        System.out.println("Your date in European form is:");
        System.out.println(euDate);
    }
}

Answer 3

Scanner kbd = new Scanner(System.in);
        String usString = kbd.nextLine();
        String[] stringArray = usString.split("(\\/|\\.)");
        String month = stringArray[0];
        String day = stringArray[1];
        String year = stringArray[2];
        System.out.println("m"+month+"d"+day+"y"+year);

This code shows how to use RegEx to split the sting into a string array which can then be re assembled into EU format without the DateFormat class.