Jagged Array in Java — Java Technical Interview Questions & Answers

Jagged Array in Java

Jagged Array in Java

  • Jagged Array is about Java arrays. An array is a fixed-size row of the same type. Index from 0. Length is a.length (a field, not a method). Last valid index is length - 1.
  • Create Jagged Array: int[] a = new int[5]; or int[] a = {10, 20, 30};. A 2D array is an array of arrays: int[][] m = {{1,2},{3,4}}; m[1][0] is 3. Jagged means rows can have different lengths.
  • Jagged Array size cannot grow. If you need grow/shrink, use ArrayList. Out of range → ArrayIndexOutOfBoundsException.
  • Let's take this on the board with one tiny Main class — no extra files. Jagged Array in Java — prints length 3, middle value 20, then all values. Start from main, go line by line, and stop at each print. That output is the proof for Jagged Array.
  index →  0    1    2
  array → [10,  20,  30]
           ↑         ↑
         first   length-1

Technical Interview Tip: Contrast array vs ArrayList in one line.

Code Examples for Jagged Array in Java

Example

// Array demo
public class Main {
  public static void main(String[] args) {
    int[] nums = {10, 20, 30};
    System.out.println(nums.length);
    System.out.println(nums[1]);
    for (int n : nums) System.out.print(n + " ");
  }
}

Jagged Array in Java — prints length 3, middle value 20, then all values.

How to Explain Jagged Array in Java to an Interviewer

What is Jagged Array?

Jagged Array — array = fixed-size, same type, index from 0. Jagged Array — a.length is a field. Last index = length - 1. Jagged Array — 2D = array of arrays. Jagged = rows of different length.

Why do we use Jagged Array in Java?

Makes the program clearer or safer Jagged Array — array = fixed-size, same type, index from 0.

Write one small example of Jagged Array.

Show syntax Say what prints

What mistake do beginners make with Jagged Array?

Only the name, no example Jagged Array — a[a.length] crashes. Size cannot grow — use ArrayList.

Where is Jagged Array used in a real program?

Day-to-day Java code