ChallengeOne.java

import java.util.List;
import java.util.Arrays;
class Challenge {
  
    private static Integer[] input;
	private static int inputLength;
	private static String concatBinary;
	private static int resultantValue;

	
	public static Integer arrayPacking(List<Integer> integers)
	{
		//Initialise values
        input = null;
        inputLength = 0;
        concatBinary = "";
        resultantValue = 0;
        
        //First ensure numbers are between 0 and 255, if not prevent further execution
		if(checkNumberBoundaries(integers))
		{
			input = new Integer[integers.size()];
			input = integers.toArray(input);
			inputLength = input.length;
			
			concatBinary = createConcatenatedBinaryString();
			
			resultantValue = binaryToDecimal(concatBinary);
			System.out.println("Result: " + resultantValue);
			
			return resultantValue;
		}
		else
		{
			System.out.println("Input numbers are not between 0 and 255");
			return -1; //Indicates error
		}
	}
	
	/*
	 * Convert decimal value into binary representation
	 * @param int input - integer with decimal value to convert
	 * @return String outString - binary representation of integer parameter
	 */
	public static String decimalToBinary(int input)
	{
		String outString = Integer.toBinaryString(input);
		
		//Concatenates a 0 onto the beginning of the string whilst the binary string's length is less than 8
		while(outString.length() < 8)
		{
			outString = "0" + outString;
		}
		
		System.out.println("Output: " + outString);
		
		return outString;
	}
	
	/*
	 * Create long binary string from concatenated binary strings
	 * @param - none
	 * @return - Long concatenated binary string
	 */
	public static String createConcatenatedBinaryString()
	{
		
		//For loop used in reverse to ensure correct placement of binary strings
		for(int i = inputLength-1; i >= 0; i--)
		{
			String binaryStr = decimalToBinary(input[i]);
			concatBinary = concatBinary + binaryStr; 
		}
		
		System.out.println("Long binary string: " + concatBinary);
		
		return concatBinary;
	}
	
	/*
	 * Convert binary string back to decimal value
	 * @Param String input - String holding value of binary string to be converted to decimal
	 * @Return int decVal - integer representation of binary string parameter
	 */
	public static int binaryToDecimal(String input)
	{
		int decVal = Integer.parseInt(input, 2);
		return decVal;
	}
	
	/*
	 * Ensures numbers held in input List are between 0-255
	 * @Param List<Integer> input - List holding input integers
	 * @Return boolean inputOkay - boolean determining if List contents are legal
	 */
	public static boolean checkNumberBoundaries(List<Integer> input)
	{
		boolean inputOkay = true;
		
		for(Integer n : input)
		{
			if(n > 255 || n < 0)
			{
				inputOkay = false;
			}
		}
		
		return inputOkay;
	}