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Jagged Array in Java

Theory

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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.

Diagram

index →  0    1    2
  array → [10,  20,  30]
           ↑         ↑
         first   length-1

Exam tip

Contrast array vs ArrayList in one line.

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.

Short notes

DefJagged Array — array = fixed-size, same type, index from 0.
RuleJagged Array — a.length is a field. Last index = length - 1.
RememberJagged Array — 2D = array of arrays. Jagged = rows of different length.
TrapJagged Array — a[a.length] crashes. Size cannot grow — use ArrayList.

// 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

Example

Short notes

Questions

Jagged Array in Java

Example

Short notes

Questions