Nested for loop in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a nested for loop in Java?

A nested for loop is a for loop inside another for loop. It lets you repeat actions in a grid or table-like way, like rows and columns.

beginner

How many times does the inner loop run if the outer loop runs 3 times and the inner loop runs 4 times each time?

The inner loop runs 4 times for each of the 3 outer loop runs, so 3 × 4 = 12 times in total.

beginner

What is the output of this code?

for (int i = 1; i <= 2; i++) {
  for (int j = 1; j <= 3; j++) {
    System.out.print(i + "-" + j + " ");
  }
  System.out.println();
}

The output is: 1-1 1-2 1-3 2-1 2-2 2-3 This shows the outer loop number paired with each inner loop number.

beginner

Why do we use nested for loops?

We use nested for loops to handle tasks that need multiple levels of repetition, like printing tables, grids, or working with multi-dimensional arrays.

intermediate

What happens if you swap the inner and outer loops in a nested for loop?

Swapping loops changes the order of repetition. The inner loop becomes the outer loop and vice versa, which can change the output pattern or how data is processed.

How many times will the inner loop run in this code?

for (int i = 0; i < 5; i++) {
  for (int j = 0; j < 2; j++) {
    // inner loop body
  }
}

A 5 times

B 2 times

C 10 times

D 7 times

The inner loop runs 2 times for each of the 5 outer loop runs, so 5 × 2 = 10 times.

What is the purpose of the inner loop in a nested for loop?

A To run once

B To stop the outer loop

C To declare variables

D To repeat actions multiple times for each outer loop iteration

The inner loop repeats its actions multiple times for each time the outer loop runs.

Which of these is a correct nested for loop structure in Java?

A for (int i=0; i<3; i++) { for (int j=0; j<2; j++) { /* code */ } }

B for (int i=0; i<3; i++) { int j=0; while(j<2) { /* code */ } }

C while (i<3) { for (int j=0; j<2; j++) { /* code */ } }

D for (int i=0; i<3; i++) { if (j<2) { /* code */ } }

Option A shows a proper nested for loop with one for loop inside another.

What will this code print?

for (int i=1; i<=2; i++) {
  for (int j=1; j<=2; j++) {
    System.out.print(i*j + " ");
  }
}

A 1 2 2 4

B 1 1 2 2

C 2 4 1 2

D 1 2 3 4

The output is 1*1=1, 1*2=2, 2*1=2, 2*2=4 printed in sequence.

If the outer loop runs 4 times and the inner loop runs 3 times, how many total iterations happen?

A 7

B 12

C 1

D 3

Total iterations = outer loop count × inner loop count = 4 × 3 = 12.

Explain what a nested for loop is and give a simple example in Java.

Think about loops inside loops and how they repeat actions.

Describe a real-life situation where you might use a nested for loop.

Imagine rows and columns in a spreadsheet or seats in a theater.