Unit 3: Boolean Expressions & if Statements

AP Computer Science A

What you'll master in this unit

The flow of control

java
int score = 85;

if (score >= 90) {
    System.out.println("A");          // skipped
} else if (score >= 80) {
    System.out.println("B");          // THIS runs
} else if (score >= 70) {
    System.out.println("C");          // skipped
} else {
    System.out.println("Below C");    // skipped
}

Key patterns at a glance

Logical operators

java
// AND — both must be true
if (age >= 16 && hasPermit) { ... }

// OR — at least one must be true
if (day.equals("Saturday") || day.equals("Sunday")) { ... }

// NOT — reverses the condition
if (!isRaining) { ... }

De Morgan's Laws

java
// These pairs are equivalent:
!(a && b)  ==  (!a || !b)
!(a || b)  ==  (!a && !b)

Why Unit 3 matters