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AssessmentPartThree.java

+
+public class AssessmentPartThree {
+
+	// The simplest form of encryption is the rotation cipher (also known as Caeser's Cipher)
+	// An offset value is chosen to encrypt a message. Each letter is replaced by the
+	// letter that that number of places away from it.
+	// So if an offset value of 1 is chosen, each letter is replaced by the one after it
+	// - so a becomes b, b becomes c, etc
+	// If a value of -2 is chosen a becomes y, b becomes z and so on
+	
+	 public char enryptedCharacter(char theChar, int theOffset)
+	 {
+		 
+		 // 05 - encryptedCharacter
+		 // Complete this method so that it returns the encrypted character for
+		 // theChar when and offset of theOffset is used
+		 // So if theChar='m' and theOffset is 3 the method will return 'p'
+		 // Lower case characters remain lower case, upper case remain upper case
+		 // Any other characters are returned unchanged
+		 
+		 //this line of code creates an instance of a stringbuilder called sb(stringbuilder for short)
+		 StringBuilder sb = new StringBuilder();
+		 //this line of code creates a string that is equal to the value of the character
+		 String character = String.valueOf(theChar);
+		 
+		 //this line of code converts the string to an array of characters
+		 for (char i: character.toCharArray())
+		 {
+			 //this line of code checks whether the character is a letter, if it is then it runs the code
+			 if (Character.isLetter(i)) {
+				 //this checks whether the letter is uppercase
+	                if (Character.isUpperCase(i)) {
+	                	//this line of code works out the new character and then adds it to the stringbuilder
+	                    sb.append((char) ('A' + (i - 'A' + theOffset) % 26 ));
+	             //this section of code is executed if the letter is lowercase
+	                } else {
+	                	//this line of code works out the new character and then adds it to the stringbuilder
+	                    sb.append((char) ('a' + (i - 'a' + theOffset) % 26 ));
+	                }
+
+			 } 
+			 //this section of code is executed if the character is not a letter
+			 else {
+				 	//this adds the character to the string builder, without making any changes
+	                sb.append(i);
+	            }
+	        
+	        }
+		 //this creates a char type variable to represent the new encrypted character
+		 char encryptedChar = sb.charAt(0);
+		 //this returns the encrypted character
+		 return encryptedChar;
+	 }
+	 
+	 public String encryptedString(String theMessage, int theOffset)
+	 {
+		 // 06 - encryptedMessage
+		 // Complete this method so that it uses encryptedCharacter to 
+		 // return the encrypted version of theMessage using theOffset
+		 
+		 //creates an instance of a stringbuilder called sb
+		 StringBuilder sb = new StringBuilder();
+		 
+		 //creates a for loop that will iterate for the number of characters in the string theMessage
+		 for (int i=0; i < theMessage.length(); i++) {
+		
+			 //this divides the offset by 26 and then adds 26 after
+			 theOffset = theOffset % 26 + 26;
+		 	//this creates a character that is equal to the current character in the string
+			 char character = theMessage.charAt(i);
+		 	//this creates a variable to represent the encrypted character, using the method encryptedCharacter to work out what the encryption should be
+			 char encodedChar =	this.enryptedCharacter(character, theOffset);
+			 
+		 	//this adds the encoded character to the string
+			 sb.append(encodedChar);
+		 	}
+		 	//this returns the encrypted string
+		 return sb.toString();
+	 }
+	
+}

AssessmentPartThreeTest.java

+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+class AssessmentPartThreeTest {
+
+	public static AssessmentPartThree test;
+	
+	
+	@BeforeAll
+	static void setUpBeforeClass() throws Exception {
+		test = new AssessmentPartThree();
+	}
+
+	@ParameterizedTest
+	@DisplayName("Testing encryptedCharacter")
+	@CsvSource({
+					"a,5,f",
+					"q,-3,n",
+					"G,6,M",
+					"5,-3,5",
+					"T,-7,M"
+	})	
+	void testEnryptedCharacter(char theChar, int theOffset, char encChar) {
+		assertEquals(encChar,test.enryptedCharacter(theChar, theOffset));
+	}
+
+	@ParameterizedTest
+	@DisplayName("Testing encryptedString")
+	@CsvSource({
+					"hello,5,mjqqt",
+					"Java Coding,-3,Gxsx Zlafkd",
+					"dandelion,8,livlmtqwv",
+					"ktixevzout,-6,encryption"					
+	})
+	void testEncryptedString(String theMessage, int theOffset, String encMessage) {
+		assertEquals(encMessage, test.encryptedString(theMessage, theOffset));
+	}
+
+}