Java Code Example: simple login

This Java program simulates a simple login system. It prompts the user for a username and password, checks these credentials against predefined values, and then displays whether the login is successful or not. The program utilizes a static method to perform the validation and uses the Scanner class to read input from the user.

Code Example

import java.util.Scanner;

public class LoginExample {
    static boolean checkUserInput(String username, String password) {
        String pw = "123456", name = "user";

        if (username.equals(name) && password.equals(pw)) {
            return true;
        } else {
            return false;
        }
    }

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String username, password;

        System.out.println("Enter username: ");
        username = scan.next().toLowerCase();
        System.out.println("Enter password: ");
        password = scan.next().toLowerCase();

        if (checkUserInput(username, password)) {
            System.out.print("Successfully logged in");
        } else {
            System.out.print("Wrong username or password");
        }
    }
}

Output first run

Enter username: 
user
Enter password: 
123456
Successfully logged in

Output second run

Enter username: 
jason
Enter password: 
3453
Wrong username or password

Code Explanation

Static Method: checkUserInput

static boolean checkUserInput(String username, String password) {
    String pw = "123456", name = "user";

    if (username.equals(name) && password.equals(pw)) {
        return true;
    } else {
        return false;
    }
}
static boolean checkUserInput(String username, String password) {
    String pw = "123456", name = "user";

    if (username.equals(name) && password.equals(pw)) {
        return true;
    } else {
        return false;
    }
}

Description

The checkUserInput method validates the provided username and password against predefined values.

Parameters

• username (String): The username entered by the user.
• password (String): The password entered by the user.

Implementation

• Step 1: Define local variables pw and name with predefined values "123456" and "user", respectively.
• Step 2: Check if the provided username equals name and password equals pw using the equals method.
• Step 3: Return true if both conditions are met; otherwise, return false.

Main Method

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String username, password;

    System.out.println("Enter username: ");
    username = scan.next().toLowerCase();
    System.out.println("Enter password: ");
    password = scan.next().toLowerCase();

    if (checkUserInput(username, password)) {
        System.out.print("Successfully logged in");
    } else {
        System.out.print("Wrong username or password");
    }
}

Description

The main method is the entry point of the program. It reads the username and password from the user, calls the checkUserInput method to validate the credentials, and displays the login result.

Implementation

• Step 1: Create a Scanner object to read input from the console.
• Step 2: Declare variables username and password to store the user’s input.
• Step 3: Prompt the user to enter the username and read the input using the next method, converting it to lowercase.
• Step 4: Prompt the user to enter the password and read the input using the next method, converting it to lowercase.
• Step 5: Call the checkUserInput method with username and password as arguments.
• Step 6: Print “Successfully logged in” if the method returns true; otherwise, print “Wrong username or password”.