Instructions:

https://www.codewars.com/kata/57f14afa5f2f226d7d0000f4/train/java

Solution:

public class Kata{	private static final String first = "qwertyuiop";	private static final String second = "asdfghjkl";	private static final String third = "zxcvbnm,.";	private static Character lower(Character c) {		if (c == '<') {			return ',';		} else if (c == '>') {			return '.';		} else if (Character.isUpperCase(c)) {			return Character.toLowerCase(c);		} else {			return c;		}	}	private static Character upper(Character c) {		if (c == ',') {			return '<';		} else if (c == '.') {			return '>';		} else if (Character.isLowerCase(c)) {			return Character.toUpperCase(c);		} else {			return c;		}	}	private static Character rotate(final Character c, String key, int direction) {		Character lower = lower(c);		String region = null;		int index = -1;		if (first.indexOf(lower) != -1) {			index = 0;			region = first;		} else if (second.indexOf(lower) != -1) {			index = 1;			region = second;		} else if (third.indexOf(lower) != -1) {			index = 2;			region = third;		}		if (region == null) {			return c;		} else {			int pos = region.indexOf(lower);			int step = Integer.valueOf(String.valueOf(key.charAt(index)));			pos = pos + step * direction;			if (pos >= region.length()) {				pos = pos % region.length();			} else if (pos < 0) {				pos = region.length() + pos;			}			if (c == lower) {				return region.charAt(pos);			} else {				return upper(region.charAt(pos));			}		}	}	public static String encrypt(String text, int key) {		String strkey = String.format("%03d", key);		StringBuilder sb = new StringBuilder();		for (int i = 0; i < text.length(); i++) {			sb.append(rotate(text.charAt(i), strkey, 1));		}		return sb.toString();	}	public static String decrypt(String encryptedText, int key) {		String strkey = String.format("%03d", key);		StringBuilder sb = new StringBuilder();		for (int i = 0; i < encryptedText.length(); i++) {			sb.append(rotate(encryptedText.charAt(i), strkey, -1));		}		return sb.toString();	}}

Sample Tests:

import org.junit.Test;import static org.junit.Assert.assertEquals;import org.junit.runners.JUnit4;public class SolutionTest {    @Test    public void encryptExampleTests() {        assertEquals("S", Kata.encrypt("A", 111));        assertEquals("Smb", Kata.encrypt("Abc", 212));        assertEquals("Wave", Kata.encrypt("Wave", 0)); // -> 000        assertEquals("Tg.y", Kata.encrypt("Wave", 345));        assertEquals(">fdd", Kata.encrypt("Ball", 134));        assertEquals(">gff", Kata.encrypt("Ball", 444));            assertEquals("Iaqh qh g iyhi,", Kata.encrypt("This is a test.", 348));        assertEquals("Sr pgi jlpl Jr,lqlage Zlow Piapc I.skiaa dw. l.s ibnepizi.p ugi. de.se.f l arkwper.c", Kata.encrypt("Do the kata Kobayashi Maru Test. Endless fun and excitement when finding a solution.", 583));              }        @Test    public void decryptExampleTests() {        assertEquals("A", Kata.decrypt("S", 111));        assertEquals("Abc", Kata.decrypt("Smb", 212));        assertEquals("Wave", Kata.decrypt("Wave", 0)); // -> 000        assertEquals("Wave", Kata.decrypt("Tg.y", 345));        assertEquals("Ball", Kata.decrypt(">fdd", 134));        assertEquals("Ball", Kata.decrypt(">gff", 444));            assertEquals("This is a test.", Kata.decrypt("Iaqh qh g iyhi,", 348));        assertEquals("Do the kata Kobayashi Maru Test. Endless fun and excitement when finding a solution.", Kata.decrypt("Sr pgi jlpl Jr,lqlage Zlow Piapc I.skiaa dw. l.s ibnepizi.p ugi. de.se.f l arkwper.c", 583));    }}