How to find Triplets whose sum is divisible by 9 from the given array of Integers ?

package pack1;

import java.util.List;

public interface TripletsSumDivBy9Intf {

	/* Define the functional interface with SAM 'ParseEachWord' */
	List<List<Integer>> ParseAnArrayInput(Integer arrVal[]);

	/* Define the static method 'displayMsg' */
	static void displayMsg(List<List<Integer>> tripletsList) {
		System.out.println(tripletsList);
	}
}

package pack1;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.function.Predicate;
import java.util.logging.Logger;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

class ArrayInput {

	private Integer[] arrIntVals;

	/* Declare the logger object for the class to display the log messages */
	static Logger logger = Logger.getLogger(ArrayInput.class.getName());

	public boolean validateInputs(Integer[] inputAnIntegerArray) {

		/* Fetch the class object's name from which this method is called */
		String cName = Thread.currentThread().getStackTrace()[2].getClassName();
		String mName = "validateInputs()";
		logger.info("This method '" + mName + "' called from the Class '" + cName + "'");

		/* Validating the function parameters using Optional Integer Array data type */
		Optional<Integer[]> arrInput = Optional.ofNullable(inputAnIntegerArray);

		/*
		 * Fetch the value of the Optional Integer Array parameters using 'isPresent'
		 * condition check. If the value is available use 'get' method otherwise simply
		 * return 'false' to stop the program execution without proceeding further.
		 */
		if (arrInput.isPresent()) {
			setArrIntVals(arrInput.get());
		} else {
			return false;
		}

		logger.info("The provided Input validated Successfully");
		return true;
	}

	/* Define getter and setters for arrIntVals Array variable */

	public Integer[] getArrIntVals() {
		return arrIntVals;
	}

	public void setArrIntVals(Integer[] arrIntVals) {
		this.arrIntVals = arrIntVals;
	}
}

class TripletsSumDivBy9_Using_Arrays extends ArrayInput implements TripletsSumDivBy9Intf {

	public List<List<Integer>> ParseAnArrayInput(Integer[] inpArr) {

		/* Fetch the class object's name from which this method is called */
		String cName = Thread.currentThread().getStackTrace()[2].getClassName();
		String mName = "ParseAnArrayInput";
		logger.info("This method '" + mName + "' called from the Class '" + cName + "'");

		/* Define an Array List of List of Integers */
		List<List<Integer>> allTripletsList = new ArrayList<List<Integer>>();

		if (validateInputs(inpArr)) {

			int sizeOfArr = getArrIntVals().length;
			System.out.println("The given input Array values are");
			/* Traversing an array to display the values */
			System.out.print("[ ");
			for (int i = 0; i < getArrIntVals().length; i++)
				System.out.print(getArrIntVals()[i] + " ");
			System.out.println("]");
			/*
			 * Traverse through an array using nested for loop, and check whether the sum of
			 * the any three successive numbers divisible by 9
			 */
			for (int i = 0; i < sizeOfArr; i++) {
				for (int j = i + 1; j < sizeOfArr; j++) {
					for (int k = j + 1; k < sizeOfArr; k++) {
						int sum = getArrIntVals()[i] + getArrIntVals()[j] + getArrIntVals()[k];
						if (sum % 9 == 0)
							allTripletsList.add(new ArrayList<Integer>(
									Arrays.asList(getArrIntVals()[i], getArrIntVals()[j], getArrIntVals()[k])));
					}
				}
			}
		} else
			logger.info("The given Input Array is null");

		TripletsSumDivBy9Intf.displayMsg(allTripletsList);
		return allTripletsList;
	}
}

class TripletsSumDivBy9_Using_Predicates extends ArrayInput implements TripletsSumDivBy9Intf {

	public List<List<Integer>> ParseAnArrayInput(Integer[] inpArr) {

		/* Fetch the class object's name from which this method is called */
		String cName = Thread.currentThread().getStackTrace()[2].getClassName();
		String mName = "ParseAnArrayInput";
		logger.info("This method '" + mName + "' called from the Class '" + cName + "'");
		/*
		 * Define the Predicate which returns true/false if the provided number
		 * divisible by 9
		 */
		Predicate<Integer> div9 = (i) -> i % 9 == 0;

		/* Define an Array List of List of Integers */
		List<List<Integer>> allTripletsList = new ArrayList<List<Integer>>();

		if (validateInputs(inpArr)) {

			int sizeOfArr = getArrIntVals().length;
			System.out.println("The given input Array values are");
			/* Traversing an array to display the values */
			System.out.print("[ ");
			for (int i = 0; i < inpArr.length; i++)
				System.out.print(inpArr[i] + " ");
			System.out.println("]");
			/*
			 * Traverse through an array using nested for loop, and check whether the sum of
			 * the any three successive numbers divisible by 9
			 */
			for (int i = 0; i < sizeOfArr; i++) {
				for (int j = i + 1; j < sizeOfArr; j++) {
					for (int k = j + 1; k < sizeOfArr; k++) {
						if (div9.test(getArrIntVals()[i] + getArrIntVals()[j] + getArrIntVals()[k]))
							allTripletsList.add(new ArrayList<Integer>(
									Arrays.asList(getArrIntVals()[i], getArrIntVals()[j], getArrIntVals()[k])));
					}
				}
			}
		} else
			logger.info("The given Input Array is null");

		TripletsSumDivBy9Intf.displayMsg(allTripletsList);
		return allTripletsList;
	}
}

class TripletsSumDivBy9_Using_Stream_and_Predicates extends ArrayInput implements TripletsSumDivBy9Intf {

	public List<List<Integer>> ParseAnArrayInput(Integer[] inpArr) {

		/* Fetch the class object's name from which this method is called */
		String cName = Thread.currentThread().getStackTrace()[2].getClassName();
		String mName = "ParseAnArrayInput";
		logger.info("This method '" + mName + "' called from the Class '" + cName + "'");
		/*
		 * Define the Predicate which returns true/false if the provided number
		 * divisible by 9
		 */
		Predicate<Integer> div9 = (i) -> i % 9 == 0;

		/* Define an Array List of List of Integers */
		List<List<Integer>> allTripletsList = new ArrayList<List<Integer>>();

		if (validateInputs(inpArr)) {

			int sizeOfArr = getArrIntVals().length;
			System.out.println("The given input Array values are");
			/* Traversing the array to display the values */
			Arrays.stream(inpArr).forEach(x -> System.out.print(x + " "));
			System.out.println("\nThe triplets of numbers which are divisible by 9");
			/*
			 * Using the nested IntStream (3 levels), flatMap, and filter return list
			 * objects as triplets, the criteria is sum of each triplet is divisible by 9
			 */
			allTripletsList = IntStream.range(0, sizeOfArr).boxed().flatMap(i -> IntStream.range(i + 1, sizeOfArr)
					.boxed()
					.flatMap(j -> IntStream.range(j + 1, sizeOfArr)
							.filter(k -> div9.test(getArrIntVals()[i] + getArrIntVals()[j] + getArrIntVals()[k]))
							.mapToObj(k -> Arrays.asList(getArrIntVals()[i], getArrIntVals()[j], getArrIntVals()[k]))))
					.collect(Collectors.toList());
		} else
			logger.info("The given Input Array is null");

		TripletsSumDivBy9Intf.displayMsg(allTripletsList);
		return allTripletsList;
	}
}

public class TripletsSumDivBy9J8 {

	public static void main(String args[]) {

		/*
		 * create the class object TripletsSumDivBy9_Using_Arrays, and call the method
		 * ParseAnArrayInput
		 */
		TripletsSumDivBy9_Using_Arrays TSDBUA = new TripletsSumDivBy9_Using_Arrays();
		Integer[] intArr = { 14, 20, 11, 5, 29, 17, 58 };
		TSDBUA.ParseAnArrayInput(intArr);
		TSDBUA.ParseAnArrayInput(null);
		/*
		 * create the class object TripletsSumDivBy9_Using_Predicates, and call the
		 * method ParseAnArrayInput
		 */
		TripletsSumDivBy9_Using_Predicates TSDBUP = new TripletsSumDivBy9_Using_Predicates();
		TSDBUP.ParseAnArrayInput(new Integer[] { 90, 9, 0, 54, 32, 51 });
		TSDBUP.ParseAnArrayInput(null);

		/*
		 * create the class object TripletsSumDivBy9_Using_Stream_and_Predicates, and
		 * call the method ParseAnArrayInput
		 */
		TripletsSumDivBy9_Using_Stream_and_Predicates TSDBUSP = new TripletsSumDivBy9_Using_Stream_and_Predicates();
		TSDBUSP.ParseAnArrayInput(new Integer[] { 4, 13, 10, 15, 2, 37, 8 });
		TSDBUSP.ParseAnArrayInput(null);
	}
}