Learn Java Programming

// Basic for loop: init; condition; update
for (int i = 1; i <= 5; i++) {
    System.out.print(i + " ");  // 1 2 3 4 5
}

// Counting backwards
for (int i = 10; i >= 0; i -= 2) {
    System.out.print(i + " ");  // 10 8 6 4 2 0
}

// Nested loops: multiplication table
for (int row = 1; row <= 5; row++) {
    for (int col = 1; col <= 5; col++) {
        System.out.printf("%4d", row * col);
    }
    System.out.println();
}

// Iterating arrays
int[] numbers = {10, 20, 30, 40, 50};
for (int num : numbers) {
    System.out.println(num);
}

// Iterating collections
List<String> fruits = List.of("Apple", "Banana", "Cherry");
for (String fruit : fruits) {
    System.out.println(fruit.toUpperCase());
}

// Iterating a Map
Map<String, Integer> scores = Map.of("Alice", 90, "Bob", 85);
for (Map.Entry<String, Integer> entry : scores.entrySet()) {
    System.out.println(entry.getKey() + ": " + entry.getValue());
}

// while — checks condition FIRST
int count = 1;
while (count <= 5) {
    System.out.print(count + " ");
    count++;
}
// Output: 1 2 3 4 5

// do-while — runs body FIRST, then checks condition
int attempts = 0;
boolean success = false;
do {
    attempts++;
    success = tryConnection();  // runs at least once
    System.out.println("Attempt #" + attempts);
} while (!success && attempts < 5);

// Practical: read input until valid
Scanner scanner = new Scanner(System.in);
int number;
do {
    System.out.print("Enter a positive number: ");
    number = scanner.nextInt();
} while (number <= 0);

// break — exit the loop immediately
for (int i = 1; i <= 10; i++) {
    if (i == 6) break;
    System.out.print(i + " ");  // 1 2 3 4 5
}

// continue — skip current iteration, jump to next
for (int i = 1; i <= 10; i++) {
    if (i % 2 == 0) continue;  // skip even numbers
    System.out.print(i + " ");  // 1 3 5 7 9
}

// Labeled break — exit outer loop from inner loop
outer:
for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 5; j++) {
        if (i * j > 6) {
            System.out.println("Breaking at i=" + i + " j=" + j);
            break outer;  // exits BOTH loops
        }
    }
}