Java Program to enter a string and extract its Substring

In this program, we are asked to enter a string and two integer values as indexes. Using these indexes, we will extract a substring from the string. The substring will be formed by iterating through the string from the starting index to the ending index - 1 and concatenating the characters onto a new string.

The logic for this process is as follows:

• Prompt the user to enter a string and two integer indexes.
• Validate the indexes to ensure they are within the bounds of the string. If the indexes are invalid, display an error message and exit the program.
• Initialize an empty string variable to hold the extracted substring.
• Iterate through the string from the starting index to the ending index - 1, adding each character to the substring variable.
• Display the extracted substring to the user.

Code:

import java.util.*;

class SubString {
  public static void main() {
    Scanner inp = new Scanner(System.in);
    System.out.print("\n Enter String: ");
    String s = inp.nextLine();
    System.out.print("\n Enter Starting Index: ");
    int st = inp.nextInt();
    System.out.print("\n Enter Ending Index: ");
    int en = inp.nextInt();

    if (st < 0 || en > (s.length())) {
      System.out.println("Invalid Index");
      System.exit(0);
    }

    int i, k = s.length();
    String z = "";
    char c;
    for (i = st; i < en; i++) {
      c = s.charAt(i);
      z = z + c;
    }

    System.out.println("Extracted Substring: " + z);
  }
}

Output:

  Enter String: ALMOST
  Enter Starting Index: 2
  Enter Ending Index: 5
  Extracted Substring: MOS