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Control Flow

📚 Lesson 3 of 16 ⏱️ 35 min

Control Flow

35 min

Control flow statements determine the order in which program instructions are executed. Java provides conditional statements (if-else, switch) for decision-making and loops (for, while, do-while, for-each) for repetition. Understanding control flow is fundamental to programming, as it enables you to create programs that make decisions and repeat actions. Control flow structures are the building blocks of program logic.

Conditional statements allow programs to make decisions based on boolean conditions. The `if-else` statement executes code when a condition is true, with optional `else if` for multiple conditions and `else` for default behavior. The `switch` statement provides a cleaner way to handle multiple conditions based on a single value. Java 14+ introduced switch expressions that return values, making them more powerful and concise. Understanding conditionals enables you to write programs that respond to different situations.

Loops enable you to repeat code execution. The `for` loop is ideal when you know the number of iterations. The `while` loop continues as long as a condition is true. The `do-while` loop executes at least once, then checks the condition. The enhanced for loop (for-each) iterates over arrays and collections elegantly. Each loop type has its use cases, and choosing the right one improves code readability and efficiency.

The enhanced for loop (for-each) is Java's most elegant way to iterate over arrays and collections. It automatically handles iteration without needing indices or iterators. The syntax `for (Type item : collection)` is cleaner and less error-prone than traditional for loops. For-each loops are read-only (you can't modify the collection during iteration) but are perfect for most iteration needs. Understanding for-each loops helps you write cleaner, more maintainable code.

Control flow statements (`break`, `continue`, `return`) modify normal execution flow. `break` exits loops or switch statements immediately. `continue` skips the rest of the current loop iteration. `return` exits methods and optionally returns values. Labeled break and continue enable breaking out of nested loops. Understanding these statements provides fine-grained control over program execution.

Best practices include using for-each loops for array/collection iteration, using switch expressions (Java 14+) when appropriate, avoiding deeply nested conditionals (use early returns), choosing the right loop type for each situation, and keeping control flow structures clear and readable. Control flow should be intuitive and easy to follow. Understanding control flow enables you to write effective, maintainable Java programs.

Key Concepts

  • Control flow statements determine program execution order.
  • Conditional statements (if-else, switch) enable decision-making.
  • Loops (for, while, for-each) enable code repetition.
  • Enhanced for loop (for-each) is ideal for arrays and collections.
  • break, continue, and return modify execution flow.

Learning Objectives

Master

  • Using if-else and switch statements for conditional execution
  • Working with different loop types (for, while, for-each)
  • Understanding when to use each control structure
  • Using break, continue, and return effectively

Develop

  • Control flow thinking and program logic
  • Understanding when to use different loop types
  • Writing clear, maintainable control structures

Tips

  • Use for-each loops for iterating over arrays and collections.
  • Use switch expressions (Java 14+) for multiple conditions.
  • Avoid deeply nested conditionals—use early returns.
  • Choose the right loop type for each situation.

Common Pitfalls

  • Using traditional for loops when for-each would be simpler.
  • Creating deeply nested conditionals that are hard to read.
  • Forgetting break statements in switch cases, causing fall-through.
  • Modifying collections during for-each iteration, causing exceptions.

Summary

  • Control flow statements determine program execution order.
  • Conditional statements enable decision-making.
  • Loops enable code repetition.
  • Enhanced for loop is ideal for arrays and collections.
  • Understanding control flow is fundamental to Java programming.

Exercise

Write a program that uses different control flow statements to process an array of numbers.

public class ControlFlow {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        
        // Using for-each loop
        System.out.println("All numbers:");
        for (int num : numbers) {
            System.out.print(num + " ");
        }
        
        System.out.println("
\nEven numbers:");
        for (int num : numbers) {
            if (num % 2 == 0) {
                System.out.print(num + " ");
            }
        }
        
        System.out.println("
\nNumbers greater than 5:");
        for (int num : numbers) {
            if (num > 5) {
                System.out.print(num + " ");
            }
        }
    }
}

Code Editor

Output