Java: Accepts a string from the user and check whether the string is correct or not

Last update on May 13 2025 12:58:47 (UTC/GMT +8 hours)

Validate String for XYZ Rules

Write a Java program that accepts a string from the user and checks whether it is correct or not.

The conditions for getting the "correct answer" are:
a) There must be only three characters X, Y, and Z in the string, and no other characters.
b) Any string of any form such as aXYZa can get the "correct answer", where a is either an empty string or a string consisting only of the letter X;
c) If aXbZc is true, aXbYZca is also valid, where a, b, c are either empty strings or a string consisting only of the letter X.

Visual Presentation:

Sample Solution:

Java Code:

 // Importing necessary classes
import java.util.PriorityQueue;
import java.util.Scanner;

// Defining a class named "Main"
public class Main {
     
    // Static nested class "Dic" representing a pair of word and page number
    static class Dic implements Comparable{
        // Instance variables to store word and page number
        String moji;
        int page;
        
        // Parameterized constructor to initialize word and page number
        Dic(String moji, int page){
            this.moji=moji;
            this.page=page;
        }

        // Implementation of the compareTo method to define the natural order of Dic objects
        public int compareTo(Dic d) {
            if(this.moji.equals(d.moji)) {
                return this.page-d.page;
            }
            else {
                return this.moji.compareTo(d.moji);
            }
        }
    }
     
    // Main method, the entry point of the program
    public static void main(String[] args) {
        // Using the try-with-resources statement to automatically close the Scanner
        try(Scanner sc = new Scanner(System.in)){
            // Creating a PriorityQueue to store Dic objects
            PriorityQueue pq=new PriorityQueue<>();
            
            // Prompting the user to input pairs of a word and a page number
			System.out.println("Input pairs of a word and a page number:");
            
            // Reading input until there is no more input
            while(sc.hasNextLine()) {
                // Reading a line and splitting it into word and page number
                String str=sc.nextLine();
                String[] token=str.split(" ");
                String s=token[0];
                int n=Integer.parseInt(token[1]);
                
                // Creating a new Dic object and adding it to the PriorityQueue
                pq.add(new Dic(s, n));
            }
            
            // Initializing a variable to store the previous word
            String pre="";

            // Printing the word and page number in alphabetical order
            System.out.println("\nWord and page number in alphabetical order:"); 
            while(!pq.isEmpty()) {
                // Polling the smallest Dic object from the PriorityQueue
                Dic dic=pq.poll();

                // Checking if the current word is the same as the previous one
                if(dic.moji.equals(pre)) {
                    System.out.print(" "+dic.page);
                }
                else if(pre.equals("")) {
                    System.out.println(dic.moji);
                    System.out.print(dic.page);
                }
                else {
                    System.out.println();
                    System.out.println(dic.moji);
                    System.out.print(dic.page);
                }
                // Updating the previous word
                pre=dic.moji;
            }
            System.out.println();
        }
    }
}

Sample Output:

Input a string:
 XYZ
Correct format..

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to validate a string that contains only the characters X, Y, and Z following a strict pattern.
• Write a Java program to check if a string follows the pattern where any number of X's may be followed by Y's and ending with Z's.
• Write a Java program to validate strings composed solely of X, Y, and Z, ensuring at least one occurrence of each letter.
• Write a Java program to determine if a string with only X, Y, and Z is valid when its order is reversed.

Go to:

• Java Basic Part-II Programming Exercises Home ↩
• Java Exercises Home ↩

PREV : Pair Words with Page Numbers.
NEXT : Highest and Lowest Scores from Student Data.

Java Code Editor:

Contribute your code and comments through Disqus.