if/else, the ternary operator and four loop forms — plus labeled break/continue for nested loops.

if / else if / else

Java

public class Main {
    static String grade(int score) {
        if (score >= 90) return "A";
        else if (score >= 75) return "B";
        else if (score >= 50) return "C";
        else return "F";
    }

    public static void main(String[] args) {
        System.out.println(grade(95) + grade(80) + grade(60) + grade(10));
        int n = 7;
        String parity = (n % 2 == 0) ? "even" : "odd";     // ternary: an expression
        System.out.println(n + " is " + parity);
    }
}

Output

ABCF
7 is odd

Loops at a glance

Loop	Syntax	Use when
`for`	`for (int i = 0; i < n; i++)`	You need the index or a counted range
enhanced `for`	`for (T x : arrayOrIterable)`	Visiting every element, read-only
`while`	`while (cond) { … }`	Unknown number of iterations; may run 0 times
`do-while`	`do { … } while (cond);`	Body must run at least once (menus, retries)

Java

public class Main {
    public static void main(String[] args) {
        for (int i = 0, j = 10; i < j; i += 3, j -= 3)       // several variables
            System.out.print(i + ":" + j + " ");
        System.out.println();

        int[] nums = {3, 1, 4};
        int sum = 0;
        for (int x : nums) sum += x;
        System.out.println("sum=" + sum);

        int n = 1234, digits = 0;
        while (n > 0) { n /= 10; digits++; }
        System.out.println("digits=" + digits);

        int k = 100;
        do { System.out.println("runs once, k=" + k); } while (k < 10);
    }
}

Output

0:10 3:7
sum=8
digits=4
runs once, k=100

break, continue & labels

Java

public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++) {
            if (i % 2 == 0) continue;      // skip evens
            if (i > 7) break;              // stop the loop
            System.out.print(i + " ");
        }
        System.out.println();

        int[][] grid = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
        outer:
        for (int r = 0; r < grid.length; r++) {
            for (int c = 0; c < grid[r].length; c++) {
                if (grid[r][c] == 5) {
                    System.out.println("found at " + r + "," + c);
                    break outer;           // leaves BOTH loops
                }
            }
        }
    }
}

Output

1 3 5 7
found at 1,1

Common mistakes

Off-by-one: i <= arr.length → ArrayIndexOutOfBoundsException. Use i < arr.length.
Modifying the loop variable inside an enhanced for does nothing to the array — x is a copy.
Removing from a List inside a for-each throws ConcurrentModificationException — use an Iterator or removeIf.
A stray ; — for (…); or while (…); makes an empty body.
Floating-point loop counters (for (double d = 0; d != 1; d += 0.1)) may never terminate.

What is the difference between while and do-while?

How do you break out of nested loops?

Can the ternary operator replace every if/else?