Java Array length — Java Technical Interview Questions & Answers

Java Array length

Java Array length

  • Array length 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 Array length: 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.
  • Array length 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. Java Array length — 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 Array length.
  index →  0    1    2
  array → [10,  20,  30]
           ↑         ↑
         first   length-1

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

Code Examples for Java Array length

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 + " ");
  }
}

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

How to Explain Java Array length to an Interviewer

What is Array length?

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

Why do we use Array length in Java?

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

Write one small example of Array length.

Show syntax Say what prints

What mistake do beginners make with Array length?

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

Where is Array length used in a real program?

Day-to-day Java code