Logical Operators: Combining Conditions

Sometimes, making a decision requires checking more than one thing at a time. For example, to go for a drive, you need both a car and a license. In Java, we use Logical Operators to connect multiple conditions.

1. The Big Three Operators

There are three main operators you will use to build complex logic:

2. Short-Circuit Evaluation

Java is efficient. It uses "Short-Circuiting" to save time:

• With &&: If the first part is False, Java doesn't even look at the second part (because the whole thing is already doomed to be false).
• With ||: If the first part is True, Java skips the second part (because the condition is already satisfied).

3. Practical Examples

Using AND (&&)

Perfect for checking if a number falls within a specific range.

int score = 85;
if (score >= 80 && score <= 90) {
    System.out.println("You got a B!");
}

Using OR (||)

Great for flexible requirements.

boolean isHacker = true;
boolean isDeveloper = false;

if (isHacker || isDeveloper) {
    System.out.println("Access to the terminal granted.");
}

Using NOT (!)

Used to check if something is not happening.

boolean isRaining = false;

if (!isRaining) {
    System.out.println("Let's go for a walk.");
}

💻 Full Practical Example: The Loan Eligibility Checker

Copy this code to see how multiple logical operators can work together to handle a complex decision:

import java.util.Scanner;

public class LoanChecker {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter your age: ");
        int age = input.nextInt();

        System.out.print("Enter your monthly income: $");
        double income = input.nextDouble();

        System.out.print("Do you have unpaid debts? (true/false): ");
        boolean hasDebt = input.nextBoolean();

        // Condition: Age must be 18+ AND income > 2000 AND must NOT have debt
        if (age >= 18 && income > 2000 && !hasDebt) {
            System.out.println("Congratulations! You are eligible .");
        } else if (hasDebt) {
            System.out.println("denied: Please clear your debts first.");
        } else {
            System.out.println("denied: You do not meet the income or age requirements.");
        }

        input.close();
    }
}

⚠️ Order of Precedence

Just like math, logic has an order of operations:

1. ! (Highest)
2. &&
3. || (Lowest)

Pro Tip: Always use Parentheses () to make your logic clear, even if they aren't strictly required. It makes your code much easier for others (and you) to read!

💡 Challenge: The Ultimate Login

Write a program that asks the user for a Username and a Password.

1. Create a "Super User" check.
2. The user gets access if:
   • (Username is "admin" AND Password is "1234") OR (Username is "root" AND Password is "java77")
3. Print "Access Granted" or "Invalid Credentials".