Creating output of given names in order that each name is followed by other with starting letter same with preceding one.

ChainOfNames.java

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.HashMap;
import java.util.Map;

public class ChainOfNames {

	public static void main(String[] args) {
		String[] names = new String[] { "Raymond", "Nora", "Daniel", "Louie", "Peter", "Esteban" };
		String chainOfNames = createChain(names);
		System.out.println(chainOfNames);
		// outputs: Peter,Raymond,Daniel,Louie,Esteban,Nora
	}

	private static String createChain(String[] names) {

		Map<String, String> firstCharacterIndex = new HashMap<>();
		Map<String, String> lastCharacterIndex = new HashMap<>();
		for (int i = 0; i < names.length; i++) {
			String name = names[i];
			String firstCharacter = getFirstCharacter(name);
			String lastCharacter = getLastCharacter(name);
			firstCharacterIndex.put(firstCharacter, name);
			lastCharacterIndex.put(lastCharacter, name);
		}

		Deque<String> nameChain = new ArrayDeque<>();
		String head = names[0];
		String tail = names[0];
		nameChain.add(names[0]);
		while (nameChain.size() < names.length) {

			String lastCharacter = getLastCharacter(tail);
			if (firstCharacterIndex.containsKey(lastCharacter)) {
				String nextName = firstCharacterIndex.get(lastCharacter);
				nameChain.addLast(nextName);
				tail = nextName;
			} else {
				String firstCharacter = getFirstCharacter(head);
				if (lastCharacterIndex.containsKey(firstCharacter)) {
					String nextName = lastCharacterIndex.get(firstCharacter);
					nameChain.addFirst(nextName);
					head = nextName;
				}
			}
		}

		return String.join(",", nameChain);
	}

	private static String getFirstCharacter(String name) {
		return name.substring(0, 1).toLowerCase();
	}

	private static String getLastCharacter(String name) {
		int nameLength = name.length();
		return name.substring(nameLength - 1, nameLength).toLowerCase();
	}

}