Control Flow

if (x > 0) {
    System.out.println("positive");
} else if (x < 0) {
    System.out.println("negative");
} else {
    System.out.println("zero");
}

// Single-statement bodies (braces optional, but always recommended)
if (flag) doSomething();

int day = 3;
switch (day) {
    case 1:
        System.out.println("Mon");
        break;                       // break required to prevent fall-through
    case 2:
        System.out.println("Tue");
        break;
    case 6:
    case 7:                          // fall-through grouping
        System.out.println("Weekend");
        break;
    default:
        System.out.println("Other");
}

int numLetters = switch (day) {
    case "MON", "FRI", "SUN" -> 6;
    case "TUE"               -> 7;
    case "THU", "SAT"        -> 8;
    case "WED"               -> 9;
    default -> throw new IllegalArgumentException("Unknown: " + day);
};

// Yield for multi-statement arms
String result = switch (code) {
    case 1 -> "one";
    case 2 -> {
        System.out.println("computing...");
        yield "two";            // yield returns a value from a block
    }
    default -> "other";
};

static String describe(Object obj) {
    return switch (obj) {
        case Integer i when i < 0 -> "negative int: " + i;
        case Integer i            -> "int: " + i;
        case String s             -> "string of length " + s.length();
        case null                 -> "null";
        default                   -> "other: " + obj.getClass().getSimpleName();
    };
}

// Classic
for (int i = 0; i < 10; i++) {
    System.out.println(i);
}

// Multiple variables
for (int i = 0, j = 10; i < j; i++, j--) { ... }

// Infinite
for (;;) { ... }

// Enhanced for-each (Iterable / array)
int[] arr = {1, 2, 3, 4, 5};
for (int n : arr) {
    System.out.println(n);
}

List<String> names = List.of("Alice", "Bob");
for (String name : names) {
    System.out.println(name);
}

int i = 0;
while (i < 10) {
    System.out.println(i);
    i++;
}

// Infinite with break
while (true) {
    String input = sc.nextLine();
    if (input.equals("quit")) break;
}

int n;
do {
    System.out.print("Enter positive: ");
    n = sc.nextInt();
} while (n <= 0);

// break — exit current loop or switch
for (int i = 0; i < 10; i++) {
    if (i == 5) break;        // exits loop when i == 5
}

// continue — skip to next iteration
for (int i = 0; i < 10; i++) {
    if (i % 2 == 0) continue; // skip even numbers
    System.out.println(i);
}

// Labeled break — exit an outer loop
outer:
for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 5; j++) {
        if (i == 2 && j == 2) break outer;  // exits both loops
    }
}

// Labeled continue
outer:
for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 5; j++) {
        if (j == 2) continue outer;          // jumps to next i
    }
}

int max = (a > b) ? a : b;
String msg = (n == 1) ? "item" : "items";

// Nested ternary (discouraged, hard to read)
String grade = score >= 90 ? "A" : score >= 80 ? "B" : "C";

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Caught: " + e.getMessage());
} catch (NullPointerException | IllegalArgumentException e) {  // multi-catch (Java 7+)
    e.printStackTrace();
} finally {
    System.out.println("Always runs");   // cleanup goes here
}

assert x > 0;                              // throws AssertionError if false
assert x > 0 : "x must be positive: " + x; // with message

// Enable assertions at runtime:
// java -ea MyClass
// Disabled by default in production.

int result = switch (x) {
    case 1 -> 10;
    default -> {
        int computed = x * x;
        yield computed;    // exit the block with a value
    }
};

String s = null;
// Safe: right side not evaluated if left is false
if (s != null && s.length() > 0) { ... }

// Safe: right side not evaluated if left is true
if (s == null || s.isEmpty()) { ... }

// Non-short-circuit (bitwise on booleans — both sides always evaluated)
if (a() & b()) { ... }
if (a() | b()) { ... }

// Variable declared in if condition (not valid in Java — unlike C/C++)
// Must declare before:
int val = getValue();
if (val > 0) { ... }

// for-loop variable scoped to the loop
for (int i = 0; i < 10; i++) { ... }
// i not accessible here

// try-with-resources — resource scoped to try block (Java 7+)
try (BufferedReader br = new BufferedReader(new FileReader("f.txt"))) {
    String line = br.readLine();
}
// br not accessible here, and auto-closed

// Common patterns for servers, event loops, retry logic
while (true) { ... }
for (;;) { ... }

// With timeout / counter guard
int attempts = 0;
while (attempts < 3) {
    try {
        doSomething();
        break;
    } catch (Exception e) {
        attempts++;
    }
}