Time Conversion 12H to 24H

Question

I wrote this code to convert 12H time to 24H time but with an input:

07:05:45pm

I get output as:

07:05:45

Here's the code

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Demo
{
static String timeConversion(String s)
{
    // Complete this function
    char a = 'a';
    char l = 0, m = 0;
    int l1 = 0, m1 = 0;
    final int RADIX = 10;
    char p = 'p';
    String str = new String();
    char t1 = 0;
    int t2 = 0;
    char arr[] = new char[10];
    arr = s.toCharArray();
    int a1 = Character.getNumericValue(arr[0]);
    int a2 = Character.getNumericValue(arr[1]);
    int t = (10*a1)+(a2);
    char _1 = '1', _2 = '2';
    if(arr[8]==p)
    {
        if((arr[0]==(_1))&&(arr[1]==(_2)))
        {
            char arr1[] = new char[8];
            for(int i = 0; i < 8; i++)
                arr1[i] = arr[i];
            str=String.copyValueOf(arr1);
        }
        else
        {
            t2 = t + 12;
            l1 = (t2%10);
            t2/=10;
            m1 = (t2%10);
            m = Character.forDigit(m1, RADIX);
            l = Character.forDigit(l1, RADIX);
            arr[1] = l;
            arr[0] = m;
            char arr1[] = new char[8];
            for(int i = 0; i < 8; i++)
                arr1[i] = arr[i];
            str=String.copyValueOf(arr1);
        }
    }
    else
        {
            char arr1[] = new char[8];
            for(int i = 0; i < 8; i++)
                arr1[i] = arr[i];
            str=String.copyValueOf(arr1);
        }
    return str;

}

public static void main(String[] args)
{
    //Scanner in = new Scanner(System.in);
    //String s = in.next();
    String s = "07:05:45PM";
    String result = timeConversion(s);
    System.out.println(result);
}
}    

As you can see I've hard coded the input becuse intellij won't allow me to pass command line arguments so I would also like to know how to pass command line argumnets in intellij.

Also, it would be really helpful if you would suggest me some good coding habits after looking at my code.

Answer 1

I wrote this code to convert 12H time to 24H time but with an input:

The fist thing I would check for you is in the condition arr[8]==p; here p='p' from a previous line, but in the string this array index is passing 'P' which is a separate char due to capitalization.

Also, it would be really helpful if you would suggest me some good coding habits after looking at my code.

As to you second point about suggesting habits, comment, comment, comment. Comments will help in explaining what you are doing to another end user and, perhaps more importantly, yourself. It's a bit like Rubber Duck Debugging. Secondly, give your variables more intuitive names; your variable names are all very generic and it takes time to refer back to declarations to see what is going on.

Answer 2

import java.text.SimpleDateFormat;
import java.util.Date;

public class HelloWorld
{
    public static void main(String [] args) throws Exception
    { 
        SimpleDateFormat displayFormat = new SimpleDateFormat("HH:mm");
        SimpleDateFormat parseFormat = new SimpleDateFormat("hh:mm a"); 
        System.out.println(displayFormat.format(parseFormat.parse("07:05 PM")));
    }
}

Answer 3

tl;dr

LocalTime
    .parse("07:05:45PM", DateTimeFormatter.ofPattern("hh:mm:ssa"))
    .toString()

---

Java new Date/Time API

One alternative is to use the built-in date/time API's.

If you're using Java 8, consider using the new java.time API. It's easier, less bugged and less error-prone than the old APIs.

If you're using Java <= 7, you can use the ThreeTen Backport, a great backport for Java 8's new date/time classes. And for Android, you'll also need the ThreeTenABP (more on how to use it here).

The code below works for both. The only difference is the package names (in Java 8 is java.time and in ThreeTen Backport (or Android's ThreeTenABP) is org.threeten.bp), but the classes and methods names are the same.

As we're dealing with times only (hour/minute/second), you can use a LocalTime. You'll also need a DateTimeFormatter with the specified format to parse it:

String s = "07:05:45PM";
// formatter with format "hour:minute:second" followed by "AM/PM"
DateTimeFormatter fmt = DateTimeFormatter.ofPattern("hh:mm:ssa");
// parse and get the result as a String
String result = LocalTime.parse(s, fmt).toString();
System.out.println(result);

The output will be:

19:05:45

---

It's much better to use the built-in API's than to reinvent the wheel (unless you're coding only for learning purposes).

If you want the output in a different format, just create another DateTimeFormatter with the desired pattern and use the format method. Check the javadoc for more info about all the available patterns.

Answer 4

You are providing String s = "07:05:45PM"; but considering use with char p = 'p', you should consider upper as well lower case meaning both 'p' and 'P'. Also, you have not considered 12:XX am time. e.g. 12:05 AM should show 00:05.

For providing argument to inteliJ idea, refer this.

Windows, Linux, some Macs:

ALT+SHIFT+F10, Right, E, Enter, Tab, enter your command line parameters, Enter