Guard Clauses

Part of the Logic & Flow section of Coddy's Java journey — lesson 38 of 59.

Guard clauses are conditional statements at the beginning of a method that check for invalid conditions and return early. They help make code cleaner and more readable by handling edge cases first.

Let's see a method without guard clauses:

public int divide(int num, int den) {
   if (den != 0) {
       if (num >= 0) {
           return num / den;
       } else {
           return -1;
       }
   } else {
       return -1;
   }
}

The same method with guard clauses:

public int divide(int num, int den) {
   if (den == 0) return -1;
   if (num < 0) return -1;
   return num / den;
}

After executing either code with divide(10, 2), the result is:

5

Challenge

Easy

Create a method named validatePassword that takes one argument:

A String (password) to validate

The method should use guard clauses to validate the password and return a message string based on these rules:

If password is null: return "Password cannot be null"
If password is empty: return "Password cannot be empty"
If password length is less than 8: return "Password must be at least 8 characters"
If password contains spaces: return "Password cannot contain spaces"
If all checks pass: return "Valid password"

Cheat sheet

Guard clauses are conditional statements at the beginning of a method that check for invalid conditions and return early, making code cleaner and more readable.

Without guard clauses:

public int divide(int num, int den) {
   if (den != 0) {
       if (num >= 0) {
           return num / den;
       } else {
           return -1;
       }
   } else {
       return -1;
   }
}

With guard clauses:

public int divide(int num, int den) {
   if (den == 0) return -1;
   if (num < 0) return -1;
   return num / den;
}

Try it yourself

import java.util.Scanner;

public class Main {
    public static String validatePassword(String password) {
        // Write your code here
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String password = scanner.nextLine();
        if (password.equals("null")) {
            password = null;
        }
        System.out.println(validatePassword(password));
    }
}