demo.java

import java.util.ArrayList;
import java.util.List;

public class Test {

    public static void main(String[] args) {
        String input = "the quick brown fox jumps over the lazy dog\n" +
                "Mi nombre es Salvador Montiel";
        String input2 = "the quick brownred fox jumps over the lazy dog\n";
        wordWrapping(input, 15).forEach(line -> {
            System.out.println("Line " + line.number + ": " + line.rawLine);
            line.chunks.forEach(chunk -> System.out.println("> " + chunk));
        });

        System.out.println("------------------------------------------------------------------------------------");

        wordWrapping(input2, 15).forEach(line -> {
            System.out.println("Line " + line.number + ": " + line.rawLine);
            line.chunks.forEach(chunk -> System.out.println("> " + chunk));
        });
    }

    public static List<Line> wordWrapping(String inputText, int length) {
        String[] lines = inputText.split("\n");
        List<Line> list = new ArrayList<>();

        int counter = 0;
        for (String line : lines) {
            int len = line.length();
            if (len > length) {
                List<String> chunks = getChunksFromLine(line, length);
                list.add(new Line(line, chunks, counter + 1));
            } else {
                list.add(new Line(line, new ArrayList<>(), counter + 1));
            }

            counter++;
        }

        return list;
    }

    private static List<String> getChunksFromLine(String line, int numChars) {
        List<String> list = new ArrayList<>();
        String[] words = line.split(" ");
        StringBuilder str = new StringBuilder();

        int counter = 0;
        for (String a : words) {
            // Number one represents the whitespace between str and a
            if (str.length() + 1 + a.length() <= numChars) {
                str.append(counter > 0 ? " " : "").append(a);
            } else if (str.length() <= numChars) {
                list.add(str.toString());
                str = new StringBuilder(a);
            }
            if (counter == words.length - 1) {
                list.add(str.toString());
            }

            counter++;
        }

        return list;
    }

    public static class Line {
        public final String rawLine;
        public final List<String> chunks;
        public final int number;

        public Line(String rawLine, List<String> chunks, int number) {
            this.rawLine = rawLine;
            this.chunks = chunks;
            this.number = number;
        }

        @Override
        public String toString() {
            return "Line{" +
                    "rawLine='" + rawLine + '\'' +
                    ", chunks=" + chunks +
                    ", number=" + number +
                    '}';
        }
    }

    private static List<String> _getChunksFrom(String item, int numChars) {
        String temp = item;
        List<String> list = new ArrayList<>();
        while (temp.length() >= numChars) {
            list.add(temp.substring(0, numChars));
            temp = temp.substring(numChars);
        }
        if (temp.length() > 0) list.add(temp);

        return list;
    }
}