Java Control Flow

Control flow determines the order in which statements run. By default, Java executes code top to bottom, but conditionals and loops let your programs make decisions and repeat work. This article covers if/else, switch, and the loop statements.

Conditional Statements

Conditional statements run different code depending on whether a condition is true or false.

The if Statement

The simplest conditional runs a block only when its condition is true.

int age = 20;
if (age >= 18) {
    System.out.println("You are an adult.");
}

The if-else Statement

Provide an alternative block for when the condition is false.

int age = 15;
if (age >= 18) {
    System.out.println("You are an adult.");
} else {
    System.out.println("You are a minor.");
}

The if-else if-else Chain

Test multiple conditions in sequence. The first matching branch runs, and the rest are skipped.

int score = 82;
if (score >= 90) {
    System.out.println("Grade: A");
} else if (score >= 80) {
    System.out.println("Grade: B");
} else if (score >= 70) {
    System.out.println("Grade: C");
} else {
    System.out.println("Grade: F");
}

The Ternary Operator

A compact way to choose between two values based on a condition.

int age = 20;
String status = (age >= 18) ? "adult" : "minor";
System.out.println(status); // adult

The form is condition ? valueIfTrue : valueIfFalse.

The switch Statement

When you compare a single variable against many constant values, switch is cleaner than a long if-else if chain.

int day = 3;
switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday");
        break;
    default:
        System.out.println("Another day");
        break;
}

• Each case compares the variable against a constant.
• break stops execution from falling through into the next case.
• default runs when no case matches (optional but recommended).

Switch Expressions

Modern Java (14+) offers a concise arrow syntax that returns a value and needs no break.

int day = 3;
String name = switch (day) {
    case 1 -> "Monday";
    case 2 -> "Tuesday";
    case 3 -> "Wednesday";
    default -> "Another day";
};
System.out.println(name); // Wednesday

switch also works with String, char, enum, and integer types.

Loops

Loops repeat a block of code while a condition holds.

The for Loop

Best when you know how many times to iterate. It combines initialization, condition, and update in one line.

for (int i = 1; i <= 5; i++) {
    System.out.println("Count: " + i);
}

• Initialization: int i = 1 runs once at the start.
• Condition: i <= 5 is checked before each iteration.
• Update: i++ runs after each iteration.

The Enhanced for Loop

Also called the “for-each” loop, it iterates over arrays and collections without an index.

int[] numbers = {10, 20, 30};
for (int number : numbers) {
    System.out.println(number);
}

The while Loop

Repeats while a condition is true. The condition is checked before each iteration, so the body may run zero times.

int i = 1;
while (i <= 5) {
    System.out.println("i = " + i);
    i++;
}

The do-while Loop

Similar to while, but the condition is checked after the body, so it always runs at least once.

int i = 1;
do {
    System.out.println("i = " + i);
    i++;
} while (i <= 5);

Branching Statements

These statements alter the normal flow inside loops.

break

Exits the loop immediately.

for (int i = 1; i <= 10; i++) {
    if (i == 5) {
        break; // stops when i reaches 5
    }
    System.out.println(i); // prints 1 to 4
}

continue

Skips the rest of the current iteration and moves to the next one.

for (int i = 1; i <= 5; i++) {
    if (i == 3) {
        continue; // skips printing 3
    }
    System.out.println(i); // prints 1, 2, 4, 5
}

return

Exits the current method entirely, optionally returning a value.

public static boolean isEven(int n) {
    if (n % 2 == 0) {
        return true;
    }
    return false;
}

Nested Control Flow

Conditionals and loops can be nested inside one another to solve more complex problems.

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        System.out.print(i * j + "\t");
    }
    System.out.println();
}

This prints a small multiplication table by placing one loop inside another.

Putting It Together

public class FizzBuzz {
    public static void main(String[] args) {
        for (int i = 1; i <= 15; i++) {
            if (i % 15 == 0) {
                System.out.println("FizzBuzz");
            } else if (i % 3 == 0) {
                System.out.println("Fizz");
            } else if (i % 5 == 0) {
                System.out.println("Buzz");
            } else {
                System.out.println(i);
            }
        }
    }
}

This classic exercise combines a for loop with an if-else if-else chain to print numbers, replacing multiples of 3 with “Fizz”, multiples of 5 with “Buzz”, and multiples of both with “FizzBuzz”.

With control flow mastered, you can write programs that make decisions and repeat work—next, learn how to organize that logic into reusable methods.