control flow

Making Decisions in Code

Control flow statements let your program choose different paths depending on conditions. Java offers if, if-else, else if, and switch for this.

The if Statement

int age = 20;

if (age >= 18) {
    System.out.println("You are an adult.");
}

The code inside the curly braces {} only runs if the condition evaluates to true.

The if-else Statement

int age = 15;

if (age >= 18) {
    System.out.println("You are an adult.");
} else {
    System.out.println("You are a minor.");
}

Chaining with else if

int score = 75;

if (score >= 90) {
    System.out.println("Grade: A");
} else if (score >= 75) {
    System.out.println("Grade: B");
} else if (score >= 60) {
    System.out.println("Grade: C");
} else {
    System.out.println("Grade: F");
}

Java checks each condition top to bottom and stops at the first one that is true. In this example, since score is 75, it prints "Grade: B" and skips the rest.

Nested Conditionals

You can place an if statement inside another one to check multiple layers of conditions:

int age = 20;
boolean hasLicense = true;

if (age >= 18) {
    if (hasLicense) {
        System.out.println("You can drive.");
    } else {
        System.out.println("You need a license first.");
    }
} else {
    System.out.println("You are too young to drive.");
}

The Ternary Operator

For simple if-else logic that just assigns a value, the ternary operator is a compact alternative:

int age = 20;
String status = (age >= 18) ? "Adult" : "Minor";

The format is: condition ? valueIfTrue : valueIfFalse.

The switch Statement

When you're comparing one variable against many possible fixed values, switch is often cleaner than a long else if chain.

int day = 3;
String dayName;

switch (day) {
    case 1:
        dayName = "Monday";
        break;
    case 2:
        dayName = "Tuesday";
        break;
    case 3:
        dayName = "Wednesday";
        break;
    default:
        dayName = "Unknown";
}

System.out.println(dayName); // Wednesday

    Important: Don't forget the break statement after each case. Without it, execution "falls through" into the next case, running its code too — even if the condition doesn't match.

Modern Switch Expressions (Java 14+)

Newer versions of Java support a more concise arrow syntax that doesn't need break:

String dayName = switch (day) {
    case 1 -> "Monday";
    case 2 -> "Tuesday";
    case 3 -> "Wednesday";
    default -> "Unknown";
};

Quick Comparison

    Coming up next: We'll explore loops — how to repeat actions using for, while, and do-while.