Control Flow

The Big Picture

Control flow directs which code runs based on conditions. Without it, code runs top to bottom every time.

• if/else: basic branching
• switch: multi-way branching on a value
• Ternary: condition ? valueA : valueB

Every program beyond hello-world uses control flow.

How It Works

The JVM evaluates boolean expressions and jumps to branches.

• if evaluates once; else if chains checked in order
• Short-circuit: && stops if left is false
• switch can compile to a jump table; mainly clearer than long if/else
• Java 14+ switch expressions return values directly
• Pattern matching (Java 21+) adds type checks to switch

In the Java Landscape

Control flow is fundamental - used in every Java construct.

• Modern switch (Java 14+): case "A" -> doA();
• Java 21 pattern switch + sealed types enables exhaustive type switches
• Optional reduces null-checking if/else chains
• Streams replace some conditional loops with filter()
• Strategy pattern replaces complex if/else with polymorphism

Pitfalls and Best Practices

• Always use braces even for single-line if blocks
• Don't nest more than 3 levels deep - extract methods
• Use early returns to flatten nested conditions
• switch fall-through is a common bug - use break
• Prefer switch expressions (Java 14+) - no fall-through
• Replace boolean flags with meaningful method names