☕ Java📅 Day 7

Loops in Java

for, while, do-while and enhanced for-each loops with break and continue.

🎯

Learning objectives

→Choose the right loop for the job
→Use break and continue to control flow
→Iterate arrays cleanly with for-each

💡 Key points

for: known number of iterations. while: condition-driven. do-while: runs at least once.
for-each (enhanced for) is the cleanest way to walk arrays and collections.
break exits the loop entirely; continue skips to the next iteration.
Infinite loop: for (;;) or while (true) — must have an internal break.

💻 Code examples(5)

#1for loop

java

for (int i = 1; i <= 5; i++) {
    System.out.println("Count: " + i);
}

Output

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

Three parts: init, condition, update. Runs while condition is true.

#2while loop

java

int n = 10;
while (n > 0) {
    System.out.println(n);
    n--;
}

Condition checked before every iteration. Zero runs if false initially.

#3do-while

java

int input;
do {
    input = readInput();   // pretend method
} while (input < 0);

Body runs at least once — condition checked at the end. Great for input validation.

#4for-each on array

java

int[] marks = {85, 90, 78, 92};
int total = 0;
for (int m : marks) {
    total += m;
}
System.out.println(total);

Output

Read as 'for each m in marks'. No index needed. Cannot modify array via m.

#5break and continue

java

for (int i = 1; i <= 10; i++) {
    if (i == 5) break;      // exit loop when i = 5
    if (i % 2 == 0) continue; // skip evens
    System.out.println(i);
}

Output

1
3

break: leave loop. continue: skip rest of body, go to next iteration.

🎯 Practice

Q1. Difference between while and do-while?+

while checks the condition first — body may run 0 times. do-while checks after — body runs at least once.

Q2. Print numbers 1-100 skipping multiples of 3.+

for (int i = 1; i <= 100; i++) { if (i % 3 == 0) continue; System.out.println(i); }

Q3. Write an infinite loop that prints 'hi' until user break.+

while (true) { System.out.println("hi"); if (shouldStop()) break; }

📝 Notes

Nested loops

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        System.out.print(i * j + " ");
    }
    System.out.println();
}

Outputs a multiplication grid. Time complexity = O(rows × cols).

Labelled break

Rare but useful — break out of both loops at once:

outer:
for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
        if (grid[i][j] == target) break outer;
    }
}