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Array of Objects in Java

Theory

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Array of Objects in Java

Array of Objects 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 of Objects: 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 of Objects 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. Array of Objects 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 Array of Objects.

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 + " ");
  }
}

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

Short notes

DefArray of Objects — array = fixed-size, same type, index from 0.
RuleArray of Objects — a.length is a field. Last index = length - 1.
RememberArray of Objects — 2D = array of arrays. Jagged = rows of different length.
TrapArray of Objects — 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 + " "); } }

Array of Objects in Java

Example

Short notes

Questions

Array of Objects in Java

Example

Short notes

Questions