Java · Theory

Multidimensional Arrays in Java

Theory

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Multidimensional Arrays in Java

A 2D array is an array of arrays. int[][] m = {{1, 2}, {3, 4}}; m[1][0] is row 1, column 0 → 3. Indexes start at 0.

Rows can have different lengths (jagged): new int[3][]; then m[0] = new int[2]; m[1] = new int[5];. Nested loops visit every cell: for i, for j.

Length — m.length is rows. m[i].length is columns in that row. Out of range still throws ArrayIndexOutOfBoundsException.

Let's take this on the board with one tiny Main class — no extra files. Multidimensional Arrays in Java — m[1][0] is row 1, column 0 → 3. Start from main, go line by line, and stop at each print. That output is the proof for Multidimensional Arrays.

Diagram

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

Exam tip

Say array of arrays. Show m[1][0]. Mention jagged if asked.

Example

public class Main {
  public static void main(String[] args) {
    int[][] m = {{1, 2}, {3, 4}};
    System.out.println(m[1][0]); // 3
  }
}

Multidimensional Arrays in Java — m[1][0] is row 1, column 0 → 3.

Short notes

Def2D array = array of arrays. m[row][col].
RuleIndex from 0. m.length = rows. m[i].length = that row’s columns.
RememberJagged = rows of different length.
TrapMixing row/col. Out of range exception.

Java · Theory

Multidimensional Arrays in Java

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Theory

51/270

Multidimensional Arrays in Java

A 2D array is an array of arrays. int[][] m = {{1, 2}, {3, 4}}; m[1][0] is row 1, column 0 → 3. Indexes start at 0.

Rows can have different lengths (jagged): new int[3][]; then m[0] = new int[2]; m[1] = new int[5];. Nested loops visit every cell: for i, for j.

Length — m.length is rows. m[i].length is columns in that row. Out of range still throws ArrayIndexOutOfBoundsException.

Diagram

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

Exam tip

Say array of arrays. Show m[1][0]. Mention jagged if asked.

Example

public class Main {
  public static void main(String[] args) {
    int[][] m = {{1, 2}, {3, 4}};
    System.out.println(m[1][0]); // 3
  }
}

Multidimensional Arrays in Java — m[1][0] is row 1, column 0 → 3.

Short notes

Def2D array = array of arrays. m[row][col].
RuleIndex from 0. m.length = rows. m[i].length = that row’s columns.
RememberJagged = rows of different length.
TrapMixing row/col. Out of range exception.

Multidimensional Arrays in Java

Example

Short notes

Questions

Multidimensional Arrays in Java

Example

Short notes

Questions