BowlingKataTests.java

package kata.bowling;

import static org.junit.Assert.*;

import org.junit.Before;
import org.junit.Test;


public class BowlingTests {

	Series series;
	
	@Before
	public void setUp() {
		series = new Series();
	}
	
	@Test
	public void testAllGutters() {
		for(int i=0;i<20;i++) series.roll(0);
		assertEquals(0, series.score());
		
		
	}

	@Test
	public void testAllStrikes() {
		for(int i=0;i<12;i++) series.roll(10);
		assertEquals(300, series.score());
	}
	
	@Test
	public void testAllOnes() {
		for(int i=0; i< 20; i++) {
			series.roll(1);
		}
		assertEquals(20, series.score());
	}
}

Series.java

package kata.bowling;

public class Series {
	
	int[] rolls = new int[21];
	int currentRoll = 0;
	
	public void roll(int pins) {
		rolls[currentRoll++] = pins;
		if (pins == 10 && currentRoll < 19) currentRoll++;
	}
	
	public int score() {
		int result = 0;
		for(int i=0;i<20;i+=2) {
			if (isStrike(i)) {
				result += 10;
				result += strikeBonus(i);
			}
			else if (isSpare(i)) {
				result += 10;
				result += rolls[i+2];
			}
			else result += rolls[i] + rolls[i+1];
		} 
		return result;
	}
	
	private int strikeBonus(int rollIndex) {
		if (lastFrame(rollIndex)) return rolls[rollIndex+1] + rolls[rollIndex+2];
		else if (nextToLastFrame(rollIndex)) return rolls[rollIndex+2] + rolls[rollIndex+3];
		
		int result = rolls[rollIndex+2];
		if (isStrike(rollIndex+2)) result += rolls[rollIndex+4];
		else result += rolls[rollIndex+3];
		return result;
	}
	
	private boolean lastFrame(int rollIndex) {
		return rollIndex == 18;
	}
	
	private boolean nextToLastFrame(int rollIndex) {
		return rollIndex == 16;
	}
	private boolean isSpare(int rollIndex) {
		return ! isStrike(rollIndex) && rolls[rollIndex] + rolls[rollIndex+1] == 10;
	}
	
	private boolean isStrike(int rollIndex) {
		return rolls[rollIndex] == 10;
	}
}