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Arrays Class in Java

Theory

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Arrays Class in Java

Arrays Class 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 Arrays Class: 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.

Arrays Class 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. Arrays Class 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 Arrays Class.

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 + " ");
  }
}

Arrays Class in Java — prints length 3, middle value 20, then all values.

Short notes

DefArrays Class — array = fixed-size, same type, index from 0.
RuleArrays Class — a.length is a field. Last index = length - 1.
RememberArrays Class — 2D = array of arrays. Jagged = rows of different length.
TrapArrays Class — 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 + " "); } }

Arrays Class in Java

Example

Short notes

Questions

Arrays Class in Java

Example

Short notes

Questions