Control Flow

Scope: if/else, switch, the three loops, and breaking out early. All samples were compiled and run with OpenJDK 21.

If and else

int temp = 85;

if (temp > 100) {
    System.out.println("Boiling");
} else if (temp > 32) {
    System.out.println("Liquid");
} else {
    System.out.println("Frozen");
}

Check: prints Liquid.

The condition must be a boolean — if (temp) doesn't compile in Java. No truthy/falsy shortcuts like Python or JavaScript; write the comparison out.

Switch

For "one variable, many exact values," switch beats a ladder of else if. The modern arrow form (Java 14+):

int day = 3;
String name = switch (day) {
    case 1 -> "Monday";
    case 2 -> "Tuesday";
    case 3 -> "Wednesday";
    default -> "Weekend-ish";
};
System.out.println(name);

Check: prints Wednesday.

The arrow form (->) returns a value and can't accidentally "fall through" into the next case — the old colon form could, which was a decades-long source of bugs. Prefer arrows.

The for loop

for (int i = 1; i <= 3; i++) {
    System.out.println("Count: " + i);
}

Check: prints Count: 1, Count: 2, Count: 3.

Three parts in the parentheses: start (int i = 1), keep going while (i <= 3), step (i++, meaning "add one"). The loop variable i exists only inside the loop.

The for-each loop

For walking through every element of an array or list:

String[] fruits = {"apple", "banana", "cherry"};
for (String fruit : fruits) {
    System.out.println(fruit);
}

Check: prints each fruit on its own line. Read the colon as "in": "for each fruit in fruits." No indexes to get wrong — use this whenever you don't need the index.

The while loop

int n = 3;
while (n > 0) {
    System.out.println(n);
    n--;
}

Check: prints 3, 2, 1. while repeats as long as the condition holds. If the condition never becomes false, the loop never ends — the classic infinite loop. (Every programmer writes one. Ctrl+C stops a runaway.)

Break and continue

for (int i = 1; i <= 10; i++) {
    if (i == 3) {
        continue;   // skip 3, keep looping
    }
    if (i == 6) {
        break;      // stop the loop entirely
    }
    System.out.println(i);
}

Check: prints 1, 2, 4, 5. continue skips to the next round; break walks out of the loop.

A note on braces

Java doesn't require braces for single-statement bodies:

if (temp > 100)
    System.out.println("Boiling");

Don't. The day someone adds a second line without adding braces, the program silently does the wrong thing. Always use braces — every linter agrees.

Next: Methods — packaging logic into reusable, named chunks.