Java confusion with hh:mm

Question

my project prompts the user for a string in form hh:mm. Then i need to separate the hh:mm into hours and minutes which i think i did

String Hour = string.substring(0,2);
String Minutes = string.substring(3,5);

Now i need to make sure that the hour is from 5<= hour < 22. But I can't do equality with a string so i used parseInt to convert it to an int and do the equality with that. But it drops leading zeroes which i need to keep in my code.

How do i go about doing this

Answer 1

Try looking at Simple Date Format

String input= "05:00";
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm");
Date date = sdf.parse(input);

Answer 2

As you asked for parseInt try

    String line = "23:59";

    String arr [] = line.split(":");
    if (Integer.parseInt(arr[0]) < 5 || Integer.parseInt(arr[0]) >= 22) {
        System.out.println("wrong hour");
    }

Answer 3

String::split

Generally, for splitting strings into parts, use the String::split command. See the Question How to split a string in Java for much discussion.

String[] parts = "07:11".split( ":" );

Arrays.toString( parts ): [07, 11]

But I do not recommend this approach in your case. Read on.

LocalTime

Java offers a purpose-built class for you: LocalTime. This class represents a time-of-day without a date and without a time zone. The clock is a single generic 24-hour day that ignores anomalies such as Daylight Saving Time (DST).

Your input such as 07:11 happens to comply with the standard ISO 8601 formats. The java.time classes use these formats by default when parsing or generating strings representing date-time values. So no need to specify a formatting pattern.

LocalTime localTime = LocalTime.parse( "07:11" );

From there you may interrogate for the hour portion or the minute portion.

int hourOfDay = localTime.getHour();
int minuteOfHour = localTime.getMinute();

But your real goal is to compare the time to see if it is between 5 AM and 10 PM. For example, is this true: 5 AM < 07:11 < 10 PM. So no need to tear apart the time into pieces. Instead, make your comparison more directly, and in a more self-documenting way, using the LocalTime class.

LocalTime start = LocalTime.of( 5 , 0 );  //  5 AM = 05:00.
LocalTime stop = LocalTime.of( 22 , 0 );  // 10 PM = 22:00.

Boolean isBetween = 
    ( ! localTime.isBefore( start ) ) 
    && 
    localTime.isBefore( stop ) 
;

See this code run live at IdeOne.com.

About that comparison statement:

• The first part asks “Is our target either exactly on the start or after the start?”. A shorter way to ask that is, “Is our target not before the start?”. If “not before” then logically it must either be exactly on or after.
• The second part asks if our target is before the stop rather than “is equal to or before”. This means we are using the Half-Open approach to defining a span of time. In Half-Open, the beginning is inclusive while the ending is exclusive. This is commonly used in date-time work. I believe using it consistently throughout your code base and business logic removes much of the confusion and ambiguity that arises from spans of time.