Java Date Class

I am looking at a website to learn Java and this is one of the exercises.

Write a program that will show different time and date information based on what number you send it. The codes are:

0 - number of milliseconds since January 1, 1970

1 - number of seconds since January 1, 1970

2 - number of days since January 1, 1970

3 - current date and time

So if I type: java prob 2
I want to see: days since January 1, 1970: 10727

I started it and used a switch statement. I am pretty sure I need to use the Date class in some way but I do not know how to put it together. If someone can show me how to do one, that would be very helpful.

public class prob4
 {
    public static void main(String args[])
    {
      String ArgumentFromCommandLine = args[0];
	  int time = Integer.parseInt(ArgumentFromCommandLine);    

        switch ( time )
    {
        case 0:
            ???;
            break;
        case 1:
            ???;
            break;
        case 2:
            ???;
            break;
        case 3:
            ???;
            break;
        default:
            System.out.println("Invalid");
    }
	
    }

}

Probably best to save 0 for invalid. No need to create a string variable before parse to int. Best check how parse handles non numeric. Start by reading the methods of Date, avoiding the SQL Date. Date (Java Platform SE 8 )

The one desired result is in the listed methods. Fill that in.

Integer.parseInt has a funny side effect though. It will convert 000 to 0, 03 to 3 and so on.

import java.util.Date; // mandatory only for the "current date and time" part

public class prob4
 {
    public static void main(String args[])
    {

    String ArgumentFromCommandLine = "";
    int time = 0;

    // exit program if the supplied argument is not an integer OR
    // if no or too many arguments were supplied
    if (args.length == 1) {
        try {
        ArgumentFromCommandLine = args[0];
            time = Integer.parseInt(ArgumentFromCommandLine);
        } catch (NumberFormatException e) {
            System.err.println("Argument " + args[0] + " must be an integer.");
            System.exit(1);
        }
    }
    else {
        System.err.println("No or too many arguments were supplied.");
            System.exit(1);
    }

    // collect all values
    Long utms = System.currentTimeMillis(); // UNIX time in milliseconds
    Long uts = utms / 1000; // UNIX time in seconds
    Long utd = uts / 86400; // UNIX time in days
    Date dateandtime = new Date(); // Current date and time, default format

    // print requested value
        switch ( time )
    {
        case 0:
            System.out.println("Milliseconds since 1970: " + utms);
            break;
        case 1:
            System.out.println("Seconds since 1970: " + uts);
            break;
        case 2:
            System.out.println("Days since 1970: " + utd);
            break;
        case 3:
            System.out.println("Current date and time: " + dateandtime);
            break;
        default:
            System.out.println("Invalid");
    }

    }

}

Oh, thank you so much! That really helps me a lot.

Well, in the land of int there are just leading bits that everyone ignores, no leading decimal zeroes.

Integer.parseInt() does not tolerate white space, just -\{0,1\}[0-9]\(1,n\} where the value must fit in 32 bits, signed. The value of n here is variable, as you can have leading zeroes in any quantity. Minus zero does not bother it, is just zero. Integer (Java Platform SE 6), int)

Looks like it blows up:

$
$ cat -n ParseInteger.java
     1  public class ParseInteger {
     2      public static void main (String[] args) {
     3          if (args.length == 1) {
     4              String strParam = args[0];
     5              System.out.println("Input string parameter                  = [" + strParam + "]");
     6              System.out.print  ("Integer value of input string parameter = ");
     7              System.out.println(Integer.parseInt(strParam));
     8          }
     9      }
    10  }
$
$ javac ParseInteger.java
$
$ java ParseInteger "-000456"
Input string parameter                  = [-000456]
Integer value of input string parameter = -456
$
$ java ParseInteger "-00"
Input string parameter                  = [-00]
Integer value of input string parameter = 0
$
$ java ParseInteger "+00"
Input string parameter                  = [+00]
Integer value of input string parameter = 0
$
$ java ParseInteger "000"
Input string parameter                  = [000]
Integer value of input string parameter = 0
$
$ java ParseInteger "1234"
Input string parameter                  = [1234]
Integer value of input string parameter = 1234
$
$ java ParseInteger "+123"
Input string parameter                  = [+123]
Integer value of input string parameter = 123
$
$ java ParseInteger ""
Input string parameter                  = []
Integer value of input string parameter = Exception in thread "main" java.lang.NumberFormatException: For input string: ""
        at java.lang.NumberFormatException.forInputString(Unknown Source)
        at java.lang.Integer.parseInt(Unknown Source)
        at java.lang.Integer.parseInt(Unknown Source)
        at ParseInteger.main(ParseInteger.java:7)
$
$
 

Yes, I meant to remove that, the API spec is very specific. Have to link wrapper it:

[Integer (Java Platform SE 6)](http://docs.oracle.com/javase/6/docs/api/java/lang/Integer.html\#parseInt\(java.lang.String, int))