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Ace the AP Computer Science Exam for High Schoolers

Solution Review: Message Encryption

Explore how to implement message encryption in Java by applying string methods such as toLowerCase, substring, and replace. Understand the step-by-step process of modifying strings to create encrypted messages, which is essential for mastering Java string manipulation in the AP Computer Science course.

We'll cover the following...

Rubric criteria

Solution

Java
class RunEncryption 
{
    public static void main(String args[]) 
    {
        // Encrypting a String
        System.out.println(encrypt("hefOP830nskdd0qSW uIm", '0', '.', "tuy83AB9"));    
    }
    // Method to encrypt the string
    public static String encrypt(String stringToBeEncrypted, char oldChar, char newChar, String extraString)
    {
        String str = stringToBeEncrypted.toLowerCase();
        String update = str.substring(0, str.length()/2) + extraString + str.substring(str.length()/2);
        return update.replace(oldChar, newChar);
    }
}

Rubric-wise explanation

Point 1:

Look at line 10. We declare the header of the encrypt method: public static String encrypt(String str). It takes four parameters: ...