diff --git a/bin/StringCalculator.class b/bin/StringCalculator.class
index a937b0c..c1acb1c 100644
Binary files a/bin/StringCalculator.class and b/bin/StringCalculator.class differ
diff --git a/bin/StringCalculatorTest.class b/bin/StringCalculatorTest.class
index d44b83f..3012e26 100644
Binary files a/bin/StringCalculatorTest.class and b/bin/StringCalculatorTest.class differ
diff --git a/src/StringCalculator.java b/src/StringCalculator.java
index 487916b..0c26689 100644
--- a/src/StringCalculator.java
+++ b/src/StringCalculator.java
@@ -1,9 +1,74 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
 
 public class StringCalculator {
 	public int add(String numbersStr) {
 		// Returns the sum of the numbers given in numbersStr
+		ArrayList<String> stringArray = new ArrayList<String>();
+		ArrayList<Integer> integerArray = new ArrayList<Integer>();
+		int result; 
+		
+		stringArray = getArrayFromString(numbersStr); 
+		try {
+			integerArray = convertArrayList(stringArray);
+		} catch (StringCalculatorException e) {
+			// TODO Auto-generated catch block
+			e.printStackTrace();
+		} 
+		result = calculateSum(integerArray);
 		
 		// not yet implemented
-		return 0;
+		return result;
+	}
+	
+	public ArrayList<String> getArrayFromString(String numbersStr){ 
+		
+		if(numbersStr == "")
+			return new ArrayList<String>(Arrays.asList("0")); 
+		
+		String[] numbers = numbersStr.split(",|\\n", -1); 
+		ArrayList<String> stringArray = new ArrayList<String>(Arrays.asList(numbers)); 
+		
+		return stringArray; 
+	}
+	
+	public ArrayList<Integer> convertArrayList(ArrayList<String> stringArray) throws StringCalculatorException{
+		
+		ArrayList<Integer> integerArray = new ArrayList<Integer>();
+		
+		boolean numeric = true;
+		int number = 0; 
+		
+		for(String stringValue : stringArray) {
+			
+			try {
+				number = Integer.parseInt(stringValue); 
+				integerArray.add(number); 
+			}catch(Exception e) {
+				numeric = false; 
+			}
+			
+			if(numeric == false) {
+				throw new StringCalculatorException(); 
+			}else if(number < 0) {
+				throw new StringCalculatorException(); 
+			}
+			
+		}
+		
+		return integerArray; 
+	}
+	
+	public int calculateSum(ArrayList<Integer> integerArray) {
+		
+		int sum = 0; 
+		
+		for(int number : integerArray) {
+			sum += number; 
+		}
+		return sum; 
 	}
+	
+	
 }
diff --git a/tests/StringCalculatorTest.java b/tests/StringCalculatorTest.java
index 4ec9afe..ea3a064 100644
--- a/tests/StringCalculatorTest.java
+++ b/tests/StringCalculatorTest.java
@@ -1,12 +1,246 @@
 import static org.junit.Assert.*;
 
+import java.util.ArrayList;
+
 import org.junit.Test;
 
 public class StringCalculatorTest {
 
+	/*
 	@Test
 	public void test() {
 		fail("Not yet implemented");
 	}
+	*/
+	
+	@Test
+	public void testGetArrayFromString_0_1() {
+		//Arrange 
+		String numbersStr = "0,1";
+		ArrayList<String> numbers = new ArrayList<String>();
+		StringCalculator calc = new StringCalculator(); 
+		String[] expectedOutput = {"0", "1"}; 
+		
+		//Act 
+		numbers = calc.getArrayFromString(numbersStr); 
+		
+		//Assert
+		assertArrayEquals(expectedOutput, numbers.toArray());
+	}
+	
+	@Test
+	public void testGetArrayFromString_1() {
+		//Arrange 
+		String numbersStr = "1";
+		ArrayList<String> numbers = new ArrayList<String>();
+		StringCalculator calc = new StringCalculator(); 
+		String[] expectedOutput = {"1"}; 
+		
+		//Act 
+		numbers = calc.getArrayFromString(numbersStr); 
+		
+		//Assert
+		assertArrayEquals(expectedOutput, numbers.toArray());
+	}
+	
+	@Test
+	public void testGetArrayFromString_EmptyString() {
+		//Arrange 
+		String numbersStr = "";
+		ArrayList<String> numbers = new ArrayList<String>();
+		StringCalculator calc = new StringCalculator(); 
+		String[] expectedOutput = {"0"}; 
+		
+		//Act 
+		numbers = calc.getArrayFromString(numbersStr); 
+		
+		//Assert
+		assertArrayEquals(expectedOutput, numbers.toArray());
+	}
+	
+	@Test
+	public void testGetArrayFromString_0_1_2_3_4_5_6() {
+		//Arrange 
+		String numbersStr = "0,1,2,3,4,5,6";
+		ArrayList<String> numbers = new ArrayList<String>();
+		StringCalculator calc = new StringCalculator(); 
+		String[] expectedOutput = {"0", "1", "2", "3", "4", "5", "6"}; 
+		
+		//Act 
+		numbers = calc.getArrayFromString(numbersStr); 
+		
+		//Assert
+		assertArrayEquals(expectedOutput, numbers.toArray());
+	}
+	
+	@Test
+	public void testConvertArray_0_1() {
+		//Arrange 
+		ArrayList<String> stringArray = new ArrayList<String>();
+		stringArray.add("0"); 
+		stringArray.add("1");
+		
+		StringCalculator calc = new StringCalculator(); 
+		
+		ArrayList<Integer> integerArray = new ArrayList<Integer>();
+		
+		ArrayList<Integer> expectedOutput = new ArrayList<Integer>(); 
+		expectedOutput.add(0); 
+		expectedOutput.add(1);
+		
+		
+		//Act 
+		try {
+			integerArray = calc.convertArrayList(stringArray);
+		} catch (StringCalculatorException e) {
+			// TODO Auto-generated catch block
+			e.printStackTrace();
+		} 
+		
+		//Assert
+		assertArrayEquals(expectedOutput.toArray(), integerArray.toArray());
+	}
+	
+	@Test
+	public void testCalculateSum_3_4() {
+		//Arrange 
+		ArrayList<Integer> integerArray = new ArrayList<Integer>(); 
+		integerArray.add(3); 
+		integerArray.add(4);
+		
+		StringCalculator calc = new StringCalculator(); 
+		
+		int expectedSum = 7;
+		
+		//Act 
+		int result = calc.calculateSum(integerArray); 
+		
+		//Assert
+		assertEquals(expectedSum, result);
+	}
+	
+	@Test
+	public void testCalculateSum_0_0() {
+		//Arrange 
+		ArrayList<Integer> integerArray = new ArrayList<Integer>(); 
+		integerArray.add(0); 
+		integerArray.add(0);
+		
+		StringCalculator calc = new StringCalculator(); 
+		
+		int expectedSum = 0;
+		
+		//Act 
+		int result = calc.calculateSum(integerArray); 
+		
+		//Assert
+		assertEquals(expectedSum, result);
+	}
+	
+	
+	@Test
+	public void testGetArrayFromString_NewLine() {
+		//Arrange 
+		String numbersStr = "1\n2,3";
+		ArrayList<String> numbers = new ArrayList<String>();
+		StringCalculator calc = new StringCalculator(); 
+		String[] expectedOutput = {"1", "2", "3"}; 
+		
+		//Act 
+		numbers = calc.getArrayFromString(numbersStr); 
+		
+		//Assert
+		assertArrayEquals(expectedOutput, numbers.toArray());
+	}
+	
+	@Test(expected = StringCalculatorException.class)
+	public void testConvertArray_Letter_StringCalculatorException() throws StringCalculatorException {
+		//Arrange 
+		ArrayList<String> stringArray = new ArrayList<String>();
+		stringArray.add("0"); 
+		stringArray.add("a");
+		
+		StringCalculator calc = new StringCalculator(); 
+		
+		ArrayList<Integer> integerArray = new ArrayList<Integer>();
+		
+		//Act 
+		integerArray = calc.convertArrayList(stringArray);
+	}
+	
+	@Test(expected = StringCalculatorException.class)
+	public void testConvertArray_DoubleValue_StringCalculatorException() throws StringCalculatorException {
+		//Arrange 
+		ArrayList<String> stringArray = new ArrayList<String>();
+		stringArray.add("0"); 
+		stringArray.add("2.34");
+		
+		StringCalculator calc = new StringCalculator(); 
+		
+		ArrayList<Integer> integerArray = new ArrayList<Integer>();
+		
+		//Act 
+		integerArray = calc.convertArrayList(stringArray);
+	}
+	
+	
+	@Test(expected = StringCalculatorException.class)
+	public void testConvertArray_NegativeNumber_StringCalculatorException() throws StringCalculatorException {
+		//Arrange 
+		ArrayList<String> stringArray = new ArrayList<String>();
+		stringArray.add("0"); 
+		stringArray.add("-1");
+		
+		StringCalculator calc = new StringCalculator(); 
+		
+		ArrayList<Integer> integerArray = new ArrayList<Integer>();
+		
+		//Act 
+		integerArray = calc.convertArrayList(stringArray);
+	}
+	
+	@Test (expected = StringCalculatorException.class)
+	public void testInvalidInput_Comma_NewLine() throws StringCalculatorException{
+		//Arrange 
+		String numbersStr = "1,\n";
+		ArrayList<String> stringArray = new ArrayList<String>();
+		StringCalculator calc = new StringCalculator(); 
+		ArrayList<Integer> integerArray = new ArrayList<Integer>();
+		
+		//Act 
+		stringArray = calc.getArrayFromString(numbersStr); 
+		integerArray = calc.convertArrayList(stringArray); 
+	}
+	
+	@Test 
+	public void testAdd_1_5_6_1_0() {
+		//Arrange
+		String numbersStr = "1,5,6,1,0"; 
+		int result; 
+		StringCalculator calc = new StringCalculator(); 
+		
+		//Act
+		result = calc.add(numbersStr); 
+		
+		//Assert
+		assertEquals(13, result); 
+	}
+	
+	@Test 
+	public void testAdd_EmptyString() {
+		//Arrange
+		String numbersStr = ""; 
+		int result; 
+		StringCalculator calc = new StringCalculator(); 
+		
+		//Act
+		result = calc.add(numbersStr); 
+		
+		//Assert
+		assertEquals(0, result); 
+	}
+	
+	
+	
 
 }