Control flow

Last reviewed May 28, 2026 Content v20260528

Track mode: server_compiled
Means: Compiled runner
Reading: ~1 min
Level: beginner

This lesson

This lesson teaches Control flow: the syntax, APIs, and habits you need before advancing in Java.

Teams ship Control flow on every Java codebase—skipping it leaves gaps in debugging and code reviews.

You will apply Control flow in contexts like: Spring Boot APIs, banking systems, Android (with Kotlin), and batch/data pipelines on the JVM.

Write Java with a public class (lessons use Main), click Run on server—the dev runner runs javac then java; fix compile errors from stderr (LEARNING_RUNNER_ENABLED=true).

When you can explain the previous lesson's ideas without copying starter code.

Java control flow matches C-family languages: if/else, switch, for, while, and enhanced for-each over arrays and collections.

if and switch

if (score >= 90) {
    grade = "A";
} else if (score >= 80) {
    grade = "B";
}

switch (day) {
    case "MON" -> System.out.println("Start week");
    case "FRI" -> System.out.println("Almost weekend");
    default -> System.out.println("Midweek");
}

Modern switch expressions (Java 14+) can return values with arrow syntax.

Loops

for (int i = 0; i < 3; i++) { }
for (String item : items) { }

Important interview questions and answers

Q: switch on String since when?
A: Java 7+ supports String in switch; use expressions in modern code.
Q: break vs continue?
A: break exits the loop; continue skips to the next iteration.

Self-check

Write the enhanced-for loop syntax for a String[].
When is a switch clearer than chained if-else?

Pitfall: Classic switch cases fall through without break—prefer arrow syntax (case X ->) in modern Java.

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Self-reflection (saved on this device)

Not saved yet.

Playground

Runs on the configured server runner (dev: npm run runner with LEARNING_RUNNER_ENABLED=true). Output appears below the editor.

Code runner not available

Server runner is disabled. Set LEARNING_RUNNER_ENABLED=true and LEARNING_RUNNER_URL in .env (see .env.example).

Check yourself

Multiple choice — immediate feedback.

Discussion

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Starter discussion topics

switch break forget?
Enhanced for vs index?

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