Fully functional

Added the String Calculator to Github

StringCalculator/src/session1/CalculateException.java

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+package session1;
+
+public class CalculateException extends RuntimeException {
+
+	private static final long serialVersionUID = 1L;
+
+	public CalculateException(String msg) {
+		super(msg);
+	}
+}

StringCalculator/src/session1/StringCalculator.java

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+package session1;
+
+public class StringCalculator {
+	public int add(String numbers) throws CalculateException {
+		// Did we get some input? Good! Lets calculate!
+		if (numbers != "") {
+			
+			// Look for negative numbers
+			if (numbers.contains("-")) {
+				throw new CalculateException("Negatives not allowed");
+			}
+
+			// Do we need another delimiter?
+			if (numbers.contains("//")) {
+				numbers = numbers.replace("\n", "");
+				String delimiter = String.valueOf(numbers.charAt(2));
+				String[] split = numbers.split(delimiter);
+				return Integer.parseInt(split[1]) + Integer.parseInt(split[2]);
+			}
+
+			// Replace all those \n with the standard delimiter
+			numbers = numbers.replace("\n", ",");
+
+			// Two delimiters? We can't have that
+			if (numbers.contains(",,")) {
+				throw new CalculateException("Two separators found.");
+			}
+
+			// A standard delimiter? Go ahead and calculate
+			if (numbers.contains(",")) {
+				String[] split = numbers.split(",");
+				return Integer.parseInt(split[0]) + Integer.parseInt(split[1]);
+			}
+			
+			// No delimiters? OK, you can have your number back them
+			else {
+				return Integer.parseInt(numbers);
+			}
+		}
+
+		// No input? Then I got nothing to do.
+		else {
+			return 0;
+		}
+	}
+}

StringCalculator/test/session1/StringCalculatorTest.java

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+package session1;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class StringCalculatorTest {
+	public StringCalculator calculator = new StringCalculator();
+
+	@Test
+	public void empty_String_Return_Zero() {
+		// Arrange
+		String numbers = "";
+
+		// Act
+		int result = calculator.add(numbers);
+
+		// Assert
+		assertEquals(0, result);
+	}
+
+	@Test
+	public void non_Empty_String_Return_3() throws Exception {
+		String numbers = "3";
+		
+		int result = calculator.add(numbers);
+		
+		assertEquals(3, result);
+	}
+	@Test
+	public void comma_Separated_Return_Sum() throws Exception {
+		String numbers = "2,3";
+		
+		int result = calculator.add(numbers);
+		
+		assertEquals(5, result);
+	}
+	
+	@Test
+	public void handle_Newlines_As_Commas() throws Exception {
+		String numbers = "4\n3";
+		
+		int result = calculator.add(numbers);
+		
+		assertEquals(7, result);
+	}
+	
+	@Test
+	public void double_Separators_Throws_Exception() throws Exception {
+		try {
+			calculator.add("4\n,5");
+			fail();
+		}catch (CalculateException e) {
+			assertEquals("Two separators found.", e.getMessage());
+		}
+	}
+	@Test
+	public void handle_Other_Delimiters() throws Exception {
+		String numbers = "//;\n5;6"; 
+		
+		int result = calculator.add(numbers);
+		
+		assertEquals(11, result);
+	}
+	@Test
+	public void no_Negatives_Allowed() throws Exception {
+		try {
+			calculator.add("3,-4");
+			fail();
+		}catch (CalculateException e) {
+			assertEquals("Negatives not allowed", e.getMessage());
+		}
+	}
+}