Module 3: Boolean Logic, Conditionals, and Enums

Key Concepts Explained

Boolean logic and enums are fundamental concepts in Java programming that help us express conditions and define fixed sets of values.

Boolean Expressions

Boolean expressions evaluate to either true or false. They form the basis for conditional logic in Java.

// Simple boolean expressions
boolean isAdult = age >= 18;
boolean hasPermission = user.isAdmin() || user.hasAccess("resource");
            

Compound Boolean Expressions

Compound expressions combine multiple boolean expressions using logical operators:

• && (AND): true only if both operands are true
• || (OR): true if at least one operand is true
• ! (NOT): inverts the value of its operand

// Compound expression with AND and OR
boolean canAccessFile = isAuthenticated && (isOwner || hasReadPermission);
            

Short-Circuit Evaluation

In Java, logical operators && and || use short-circuit evaluation. This means the second operand is only evaluated if necessary.

// Short-circuit to avoid NullPointerException
if (user != null && user.hasPermission("admin")) {
    // Second part only evaluated if user is not null
    performAdminAction();
}
            

Object Comparison with equals()

When comparing objects, use the equals() method rather than == which compares references, not content.

String name1 = "John";
String name2 = new String("John");

// Incorrect: compares references
boolean isSameReference = (name1 == name2); // false

// Correct: compares content
boolean isSameContent = name1.equals(name2); // true
            

Conditional Statements

Conditional statements use boolean expressions to control program flow:

// Simple if statement
if (temperature > 30) {
    System.out.println("It's hot outside!");
}

// if-else statement
if (score >= 70) {
    System.out.println("Passed");
} else {
    System.out.println("Failed");
}

// Nested conditionals
if (temperature > 30) {
    if (isRaining) {
        System.out.println("Hot and rainy");
    } else {
        System.out.println("Hot and dry");
    }
}
            

Enums

Enums provide a way to define a fixed set of constants, making code more readable and type-safe.

// Defining an enum
public enum DayOfWeek {
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}

// Using an enum
public class Schedule {
    public void setMeeting(String title, DayOfWeek day) {
        switch (day) {
            case MONDAY:
                System.out.println("Meeting scheduled for Monday: " + title);
                break;
            case FRIDAY:
                System.out.println("Meeting scheduled for Friday: " + title);
                break;
            default:
                System.out.println("Meeting scheduled for " + day + ": " + title);
        }
    }
}