Java Program to Print an Integer (Entered by the User)

Introduction

Java is a robust programming language widely used for building enterprise-scale applications, Android apps, and much more. One fundamental concept in any programming language is handling user inputs and displaying outputs. This forms the foundation of interactive applications.

In this article, you will learn how to create a Java program that prompts the user to enter an integer and then prints it. Explore different examples illustrating how to implement this simple but essential task using various Java methods.

Using Scanner for User Input

Basic Integer Input and Output

1. Import the Scanner class which is used to read data entered by the user.

2. Create an instance of Scanner.

3. Prompt the user to enter an integer.

4. Use the nextInt() method to read the integer.

5. Print the integer entered by the user.

   java Copy

   import java.util.Scanner;
   
   public class IntegerPrinter {
       public static void main(String[] args) {
           Scanner scanner = new Scanner(System.in);
           System.out.println("Enter an integer: ");
           int number = scanner.nextInt();
           System.out.println("You entered: " + number);
       }
   }
   

   This code snippet creates a Scanner object that reads integers from the standard input (keyboard). The program then uses System.out.println to display the integer that the user entered.

Handling Input Exceptions

1. Implement error handling to manage non-integer inputs.

2. Use a try block to attempt reading an integer.

3. Catch a potential InputMismatchException if a non-integer is entered.

4. Prompt the user again for an integer.

   java Copy

   import java.util.InputMismatchException;
   import java.util.Scanner;
   
   public class IntegerPrinter {
       public static void main(String[] args) {
           Scanner scanner = new Scanner(System.in);
           System.out.println("Enter an integer: ");
           try {
               int number = scanner.nextInt();
               System.out.println("You entered: " + number);
           } catch (InputMismatchException e) {
               System.out.println("That's not an integer. Please enter an integer.");
           }
       }
   }
   

   This enhanced version of the program includes exception handling. If the user inputs something that isn’t an integer, the InputMismatchException is caught, and a relevant message is displayed.

Using JOptionPane for Graphical User Input

Using JOptionPane for Input and Output

1. Import the JOptionPane class for using GUI elements.

2. Use JOptionPane.showInputDialog() to get user input through a dialog box.

3. Parse the input string to an integer.

4. Display the integer using JOptionPane.showMessageDialog().

   java Copy

   import javax.swing.JOptionPane;
   
   public class IntegerPrinterGUI {
       public static void main(String[] args) {
           String input = JOptionPane.showInputDialog(null, "Enter an integer:");
           try {
               int number = Integer.parseInt(input);
               JOptionPane.showMessageDialog(null, "You entered: " + number);
           } catch (NumberFormatException e) {
               JOptionPane.showMessageDialog(null, "That's not an integer. Please enter an integer.");
           }
       }
   }
   

   This version uses the JOptionPane class to create graphical dialogs for both input and output. It's a more user-friendly way and suitable for GUI applications but requires the javax.swing library.

Conclusion

Creating a Java program to print an integer entered by a user demonstrates the basic skills of handling inputs and outputs in Java. Starting with the console-based input using Scanner and advancing to graphical input with JOptionPane provides you with the flexibility to implement user interaction in both console applications and GUIs. By mastering these methods, you ensure your Java applications can interact effectively with users, enhancing both functionality and user experience.