Practical Applications of String Methods

Putting methods into practice

Now, let's dive into code examples for each of these methods. You'll quickly grasp their functionality:

Main


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package com.example;

public class Main {
    public static void main(String[] args) {
        String string = "Hello world";
        System.out.println("string length = " + string.length());
        System.out.println("char at 0s position is " + string.charAt(0));
        System.out.println("substring from third position = " + string.substring(3));
        System.out.println("substring from third to seventh position = " + string.substring(3, 7));
        System.out.println("string in lower case = " + string.toLowerCase());
        System.out.println("string in upper case = " + string.toUpperCase());
        System.out.println("checking if string contains 'ell' = " + string.contains("ell"));
        System.out.println("replacing all the 'l' characters to 'b' = " + string.replace('l', 'b'));
        char[] chars = string.toCharArray();

        System.out.println("as we can see, after all of this " +
                "operations our string hasn't changed, it is still " + string);
    }
}

We just used many methods on a single string, but in the end, its value remained unchanged. That's exactly what I mentioned in the previous chapter. The value of a string doesn't alter without creating a new object in memory.

Now, let's explore a few practical applications of these methods through the following example tasks:

Task 1

Create a program to securely encode a message. Display the encrypted message on the console.

We will write our own encryption method that shifts each character in the original string 3 positions forward in the ASCII table to encrypt the message.

Main


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package com.example;

public class Main {
    public static void main(String[] args) {
        String secretMessage = "hello world"; // Original message
        char[] codedMessage = secretMessage.toCharArray(); // Convert message to a char array
        
        // Loop through each character and shift by 3 positions in the ASCII table to encrypt
        for (int i = 0; i < codedMessage.length; i++) {
            // Encrypt character
            codedMessage[i] = (char) (codedMessage[i] + 3);
        }
        // Print the encrypted message
        System.out.println(new String(codedMessage));
    }
}

This code demonstrates a simple encryption method for a password or secret message. The string hello world is converted into a character array, and each character is shifted forward by 3 positions in the ASCII table using (char) (codedMessage[i] + 3). The encrypted message is then printed to the console.

Task 2

You upload a document title, and it needs to be converted to uppercase with underscores _ added between words to create a system-friendly filename.

Main


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package com.example;

public class Main {
    public static void main(String[] args) {
        String documentTitle = "Quarterly financial report"; // Document title
        String systemFileName = documentTitle.toUpperCase().replace(" ", "_");
        
        System.out.println(systemFileName); // Output
    }
}

This code processes a document title to create a system-friendly filename. It uses toUpperCase() to convert all letters to uppercase and replace(" ", "_") to replace spaces with underscores, ensuring consistency and compatibility for file storage. The result is then displayed on the console.

1. What will be printed to the console?

2. What will be printed to the console?

3. What will be printed to the console?

Everything was clear?

Thanks for your feedback!

Section 5. Chapter 3