Chapter 8, Problem 17E

 Creation of the class “ShuffleCipher”:

 Filename: ShuffleCipher.java

 The creation of the class “ShuffleCipher” derived from the “MessageEncoder” interface is given below:

• • Declare the “n” integer variable.
• • Define the constructor along with a parameter “n”.
  • ○ Set the value to the declared variable.
• • The “encode” method is used to encode the given plain text.
  • ○ Declare and assign the value to the variable.
  • ○ The “for” loop iterate till “n” numbers.
    • ■ Call the “shuffle” method with an argument.
      • ○ Return the encoded text.
• • The “shuffle” method is used to shuffle the text.
  • ○ Declare the “m” variable.
  • ○ Find the midterm of the given plain text for splitting into two halves.
  • ○ Declare the “a”, and “b” variables.
  • ○ Call the “substring” with the arguments and stored it “a” variable.
  • ○ Call the “substring” with the argument and stored it “b” variable.
  • ○ The “for” loop is used to append the two substrings.
  • ○ Finally return the string.

 Filename: Demo.java

 The “Demo” contains main method, it is used to get the plain text, and number of iteration from the user.

 Then create an object for the “ShuffleCipher” class.

 Call the “encode” method with the use of “ShuffleCipher” class object.

 Finally display the encoded text on the output screen.

 Filename: MessageEncoder.java

• • Declare the “encode” method along with the parameter “plainText”.
  • ○ This method take the string variable as plain text, then encodes and returns it as encoded message.

 Program:

 Filename: ShuffleCipher.java

//definition of "ShuffleCipher" class

public class ShuffleCipher implements MessageEncoder

{

    //declare the integer variable

    private int n;

    //definition of constructor

    public ShuffleCipher (int n)

    {

        //set the value

        this.n = n;

    }

    //definition of "encode" method

    public String encode(String plainText)

    {

        //declare and assign the value to the variable

        String encodedText = plainText;

        //check the condition

        for(int i = 0; i < n; i++)

        {

            //call the method

            encodedText = shuffle(encodedText);

        }

        //return the value

        return encodedText;

    }

    //definition of "shuffle" method

    private String shuffle(String t)

    {

        //declare the variable

        int m;

        //check the condition

        if (t...