String result =                                       // Text representing the value of our date-time object.
    LocalTime.parse(                                  // Class representing a time-of-day value without a date and without a time zone.
        "03:30 PM" ,                                  // Your `String` input text.
        DateTimeFormatter.ofPattern(                  // Define a formatting pattern to match your input text.
            "hh:mm a" ,
            Locale.US                                 // `Locale` determines the human language and cultural norms used in localization. Needed here to translate the `AM` & `PM` value.
        )                                             // Returns a `DateTimeFormatter` object.
    )                                                 // Return a `LocalTime` object.
    .format( DateTimeFormatter.ofPattern("HH:mm") )   // Generate text in a specific format. Returns a `String` object.
;

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

public class Main {
   public static void main(String [] args) throws Exception {
       SimpleDateFormat displayFormat = new SimpleDateFormat("HH:mm");
       SimpleDateFormat parseFormat = new SimpleDateFormat("hh:mm a");
       Date date = parseFormat.parse("10:30 PM");
       System.out.println(parseFormat.format(date) + " = " + displayFormat.format(date));
   }
}