To implement Java Programs using Strings

Explanation

This Java program is designed to determine if a smaller sequence of characters (a "substring") exists within a larger sequence of characters (a "main string"). It's a straightforward application that demonstrates basic string manipulation and user input handling in Java.

Here's a step-by-step breakdown of how the code works:

1. Import Scanner: The program starts by importing the Scanner class from Java's util package. The Scanner class is a utility that allows a program to read input from various sources, in this case, the standard input stream (keyboard).
2. Define Class: It defines a public class named SubStringExists. All Java code must reside within a class.
3. Main Method: Inside the class, there's a public static void main(String[] args) method. This is the entry point for any Java application. When you run the program, the Java Virtual Machine (JVM) starts execution from this method.
4. Create Scanner Object: An object of the Scanner class is created: Scanner input = new Scanner(System.in);. This input object is now ready to read data typed by the user into the console.
5. Prompt for Main String: The program displays a message "Enter the main string: " on the console, prompting the user to type the primary string.
6. Read Main String: It then uses input.nextLine() to read the entire line of text typed by the user (until they press Enter) and stores it in a String variable named mainString.
7. Prompt for Substring: Similarly, it prompts the user to "Enter the substring: ".
8. Read Substring: It reads the user's input for the substring using input.nextLine() and stores it in a String variable named subString.
9. Check for Substring: The core logic is in the if (mainString.contains(subString)) statement.
   • mainString.contains(subString) is a method call on the mainString object. This method checks if the subString is present anywhere within the mainString.
   • It returns true if subString is found, and false otherwise. This check is case-sensitive.
10. Display Result:
    • If contains() returns true, the program executes the code inside the if block, printing "Substring exists" to the console.
    • If contains() returns false, the program executes the code inside the else block, printing "Substring does not exist" to the console.
11. Close Scanner: Finally, input.close() is called. This is an important step for good programming practice; it releases the system resources associated with the Scanner object.

Algorithm

The algorithm used in this program can be described as follows:

1. Start: Begin the program execution.
2. Initialize Input Reader: Create an instance of the Scanner class to facilitate reading input from the console.
3. Get Main String:
   • Display a prompt asking the user to enter the main string.
   • Read the entire line of text entered by the user and store it in a string variable (e.g., mainString).
4. Get Substring:
   • Display a prompt asking the user to enter the substring to search for.
   • Read the entire line of text entered by the user and store it in a string variable (e.g., subString).
5. Check Existence:
   • Use the contains() method of the mainString to check if it includes the subString. This method performs a case-sensitive search.
6. Display Outcome:
   • If the contains() method returns true, print "Substring exists" to the console.
   • Otherwise (if contains() returns false), print "Substring does not exist" to the console.
7. Clean Up: Close the Scanner object to release system resources.
8. End: Terminate the program.